“I told them they had to get tested, and they did:” Social Influence Among Siblings with Li-Fraumeni Syndrome

Abstract

Health-related social influence refers to individual efforts to change another person’s health beliefs and/or behavior. We sought to understand perspectives on social influence among adult siblings in families with an inherited cancer syndrome, Li-Fraumeni Syndrome (LFS). An interprofessional team conducted 16 semi-structured interviews with sibling groups (n = 29, aged 18-66, 2-3 siblings per group) enrolled in the NCI’s LFS Study. A semi-structured interview guide included questions targeting family closeness, information sharing, and perspectives on screening and cancer care. The research team collaboratively conducted thematic analysis on verbatim transcripts. Participants reported attempts to influence their siblings’ thoughts or behavior regarding LFS-related genetic testing and cancer screening, prevention, and treatment. Some participants expressed respect for sibling autonomy regarding risk management decisions. Others reported explicit attempts to change their siblings’ perspective or behavior due to concern for their siblings’ health. Findings suggest participants believed their influence meaningfully affected siblings’ LFS risk management, indicating such influence comprises a social intervention pathway with potential to increase cascade testing and to support risk management. However, for some siblings, such efforts incurred risk of relational conflict. Future research might aim to help adult siblings balance social influence strategies with relational maintenance behaviors.

Hereditary cancer syndromes (e.g., hereditary breast and ovarian cancer, Li-Fraumeni Syndrome) predispose individuals to very high cancer risks and pose significant physical and psychosocial challenges for affected individuals and families. Diagnosis of a hereditary cancer syndrome frequently elicits changes in family roles and dynamics; some individuals adopt illness-specific family roles that include information gathering, gatekeeping, and/or dissemination, as well as support provision (Koehly et al., 2009). Motivations to care for loved ones may drive family members with the potential for shared risk to engage in health-related social influence—intentional attempts to modify another’s health beliefs or behaviors in alignment with perceived best practices (Huelsnitz, Jones, et al., 2022). This study extends research on social influence by examining its presence within adult sibling relationships, a critical but often understudied close relationship (Gilligan et al., 2020) in the context of hereditary cancer risk. Given that siblings often share family medical histories and similar genetic risk factors, and they must navigate complex decisions regarding testing and risk management, social influence from adult siblings may play an important role in shaping health-related behaviors and attitudes.

Li-Fraumeni Syndrome

Li-Fraumeni syndrome (LFS) is a rare inherited cancer syndrome that confers nearly 100% lifetime multi-organ cancer risk beginning in infancy. LFS is caused primarily by inherited pathogenic germline variants in the gene TP53, which are identified through genetic testing (de Andrade et al., 2021). Each child of a person with a pathogenic germline TP53 variant has a 50% chance of inheriting the variant (Kratz et al., 2017). The mean age of cancer diagnosis among individuals with LFS is 45 years old for men and 33 years old for women, with women incurring higher lifetime risk than men due to frequent early breast cancer diagnoses (de Andrade et al., 2021). Commonly occurring cancers include soft-tissue and bone sarcomas, premenopausal breast cancer, and brain tumors, among others (de Andrade et al., 2021; Schneider et al., 2024). Beyond risk-reducing mastectomy for women, LFS has limited prevention options (Siegel et al., 2021). Clinical recommendations for children and adults include intensive annual multi-organ cancer screenings to detect early-stage cancers and reduce morbidity and mortality (Achatz et al., 2025).

Family members frequently play a role in the genetic diagnosis process because their health and cancer histories provide valuable information for those undergoing genetic testing. Additionally, individuals are encouraged to share their genetic test results with untested blood relatives who may also be at risk of carrying the same pathogenic variant, a practice known as cascade testing (Roberts et al., 2018). Families with LFS often have extensive cancer histories within and across generations and may collectively experience LFS-related challenges, such as cancer (both new cancers and treatment of prevalent cancers), cancer screening burden, family role shifts (e.g., caregiving, care receiving), cancer worry, difficult reproductive decision making, and bereavement (Werner-Lin et al., 2020; Wilsnack et al., 2024). These shared experiences may lead to regular exchanges of LFS-related information and support (Rising et al., 2022). In particular, siblings may play a crucial role regarding engagement with cascade testing and risk management strategies, highlighting the unique importance of their role in families with LFS.

Sibling Relationships in the Context of Health and Genetic Illness

Sibling relationships are uniquely positioned to facilitate social influence in the context of health and genetic illness. Siblings share extensive knowledge about each other (Goetting, 1986) and may continue to influence each other in adulthood based on relational dynamics established in childhood (Cassinat et al., 2019). While most research on sibling influence has focused on childhood and adolescence (Gilligan et al., 2020), social support remains a key function of sibling relationships throughout life (Goetting, 1986; Voorpostel & Van Der Lippe, 2007). In healthcare contexts, siblings are often considered sources of emotional and instrumental support, contributing to caregiving and medical decision-making processes (Mikkelson et al., 2011; Milevsky, 2019). Although romantic partners and parents are more commonly recognized as sources of health-related social influence (Tucker et al., 2006), research suggests that siblings play a particularly crucial role in chronic familial disease management and decision-making when health issues are severe (Novak et al., 2023).

Limited work has examined the added stressors on sibling relationships when health issues are shared among siblings. Siblings are more likely to undergo cascade testing compared to parents or children of affected individuals (Bednar et al., 2020). Yet, the inherently shared nature of hereditary cancer syndromes may heighten concern among siblings, particularly when discordant decisions arise regarding these issues. For example, individuals with Lynch syndrome reported distress when a sibling opted out of cascade testing, with 13.1% citing family conflict related to testing decisions (van Oostrom et al., 2007). Such situations may prompt social influence attempts aimed at encouraging testing and adherence to risk management recommendations.

A systematic review of family adjustment to hereditary cancer syndromes found that siblings who received the same genetic test results (whether positive or negative) reported better psychological adjustment (Gomes et al., 2022). Sharing the same results was associated with reduced distress and strengthened sibling bonds (Hamann et al., 2008). Interestingly, both carriers and non-carriers of hereditary cancer mutations have reported similar levels of perceived risk and cancer worry into middle age, suggesting that sibling experiences with genetic testing are interdependent and lifelong (Koehly et al., 2008). Moreover, women with hereditary cancer syndromes have indicated that their siblings’ test results and opinions influence their own risk management decisions (Napoli et al., 2020).

Given the heightened salience of shared risk in families with LFS, social influence among siblings may serve as a mechanism not only for health preservation, but for managing worry and uncertainty. The current research investigates how siblings attempt to influence each other’s health-related decisions in the context of discordant choices regarding cascade testing and cancer surveillance for Li-Fraumeni Syndrome.

Self-Determination Theory: Autonomy-Supportive and Autonomy-Limiting Influence

Self-determination theory (SDT; Ryan & Deci, 2017), which highlights the role of important others in supporting or undermining autonomy, offers a valuable framework for examining the dyadic nature of sibling social influence in the context of hereditary cancer risk. Specifically, SDT distinguishes autonomy-supportive from autonomy-limiting behaviors. Autonomy support involves encouraging health behaviors in important others, such as acknowledging personal preferences, offering choices, and providing information without coercion (Reeve et al., 1999; Silva et al., 2010). In contrast, autonomy-limiting behaviors exert pressure or control over another’s decisions, potentially fostering resistance and distress (Ng et al., 2012). In the context of LFS, autonomy-supportive strategies might include respecting a sibling’s choice regarding cancer screening, whereas autonomy-limiting strategies might involve emphasizing the dangers of forgoing medical surveillance.

Autonomy support provision may be especially important for promoting well-being and health among individuals with Li-Fraumeni Syndrome, as cancer experiences can be autonomy limiting (e.g., Cosme & Berkman, 2020). Thus, autonomy support has been positively associated with cancer patients’ self-management (Bae & Kim, 2019) and adherence to exercise among colorectal cancer patients (Romero-Elías et al., 2024). Although research on autonomy-supportive and autonomy-limiting behaviors within sibling relationships is limited, available evidence suggests that autonomy-supportive strategies positively impact health and well-being. Most research focuses on parent-child or teacher-student relationships, but studies on sibling dynamics indicate that autonomy support is linked to higher goal progress and need satisfaction, while autonomy-limiting behaviors show no such associations (Audet et al., 2021). Additionally, autonomy support from close others, including siblings, has been found to predict greater physical activity through enhanced autonomy satisfaction (Kim et al., 2022).

Other Factors Affecting Social Influence: Directness and Attitudes Toward Influence

Directness is another feature of social influence that may have implications for relationships and health outcomes. Direct strategies explicitly encourage behavior change (e.g., reminding a sibling to schedule a screening), while indirect strategies use subtle cues, such as modeling desired behaviors or expressing concern through nonverbal gestures (Lewis & Butterfield, 2007). The role of directness in sibling influence strategies remains unexplored, yet examining these strategies may offer valuable insights into how siblings navigate social influence in the context of hereditary cancer risk. While direct influence has been shown to heighten short-term conflict in other close relationships, it may also promote adherence to health recommendations (Overall et al., 2009). Given the unique lifelong nature of sibling relationships, understanding how directness functions in this context could deepen our knowledge of familial social influence dynamics.

In addition to examining the strategies siblings use, it is also important to consider how they perceive social influence. Attitudes toward influence—such as whether siblings view it as intrusive or supportive—may shape the extent to which influence attempts are accepted or resisted. If influence is perceived as autonomy-supportive, it may strengthen sibling relationships and encourage engagement in health-protective behaviors. However, if influence is seen as controlling or coercive, it may lead to tension or resistance, ultimately undermining health-related decision-making and increasing the potential for relational conflict. Exploring these attitudes can provide insight into when and how social influence fosters positive health outcomes within sibling relationships.

Study Aim and Research Questions

Despite these findings, little is known about the most effective ways to involve adult siblings at critical points in risk-reduction decision-making (Gomes et al., 2022). To date, no research has examined the reasons why siblings enact social influence, the attitudes they hold toward social influence, or the strategies used to exert social influence. To advance sibling relationship science, this study aimed to explore social influence among siblings in a context in which it may be likely to occur, hereditary cancer syndromes, specifically LFS. We posed the following research questions: 1) What are the LFS-related health domains within which siblings exert influence?; 2) What are siblings’ attitudes toward social influence?; 3) What are the reasons for the presence or absence of social influence among siblings?; and 4) What types of influence strategies do siblings engage in?

Method

Study Design

This analysis was nested within the National Cancer Institute’s (NCI) LFS Study (clinicaltrials.gov #NCT01443468) whose primary objectives were to investigate the clinical, behavioral, epidemiological, and genetic etiology of LFS to inform global screening standards (e.g., Mai et al., 2016). From 2012-2017, we concurrently implemented a large family interview protocol to understand, characterize, and address the psychosocial impact of LFS on individuals and families (e.g., Young et al., 2019). Here we report on a secondary analysis of exploratory family discourse interview data. Our design was informed by interpretive description and grounded theory methods to leverage their person-centered and constructivist framing (Bryant & Charmaz, 2007). Interpretive description, an applied qualitative research method for developing experiential knowledge for clinical use, enabled us to develop findings relevant for family-based clinical practice (Thorne, 2016).

Family Interview Recruitment

The NCI LFS Study opened to national accrual in 2011 and is described in detail elsewhere (e.g., Wilsnack et al., 2021). The study offered genetic counseling, TP53 genetic testing, and study enrollment to at-risk family members. A purposively sampled subset of the study participants older than three years of age and with confirmed germline pathogenic TP53 variant, were offered to join the cancer screening arm of the study and attend the NCI annually for whole-body, brain, and breast MRIs (for female participants > 20 years), and physical exams. From 2012-2017, all family members aged 13 and older participating in the NCI’s LFS Study were invited to complete a family group interview, the basis of the current study. Family groups were defined as two or more individuals from the same kindred, connected by biology or law. In total, 45 families completed 66 interviews, including 117 family members (aged 13-81 years) with or without a TP53 variant. Interviews included varied constellations of family members (e.g., parent-child groups, partner dyads, sibling groups, mixed groups).

Participants: Sibling-inclusive Family Interview

All 66 family interviews were screened for the inclusion of sibling combinations, with or without the presence of other family members. The resulting 16 interviews included 13 family units with 29 individual siblings. Interviews were open to all family members. Of the sixteen interviews, 15 involved sibling pairs and one involved a sibling trio. Eight of the 16 interviews involved same-sex sibling dyads (four brother pairs and four sister pairs), and eight involved mixed-sex sibling groups. Among the 16 interviews, two included the siblings’ parent(s), two included a sibling’s adolescent child, and one included a sibling’s spouse. Most siblings 93% (93%, n = 27/29) had an LFS diagnosis and a previous cancer diagnosis (n = 22/29, 76%). Thirteen sibling groups completed one interview, and three sibling groups completed two interviews. Approximately half of participants were female (n = 15/29, 52%) and the median age at the time of the interview(s) was 36 years (range = 18-66 years). All participants identified their race as white and 10% (n = 3/29) identified their ethnicity as Hispanic. Interviews averaged 50 minutes (range = 21-81 min). Siblings were not required to participate in the interview for content about them to be included in analysis.¹

Family Group Data Collection Procedure

Primary data collection consisted of using a collaboratively designed semi-structured interview guide to explore family stories about cancer risk communication, reproductive decision-making, genetic testing decisions and experiences, and cancer risk management behaviors. A licensed marriage and family therapist (fifth author) conducted all interviews in person at the clinical center. Interviews were audio-recorded, transcribed verbatim, and de-identified before being uploaded to Dedoose^™ for analysis.

Ethics

All participants received detailed study information before providing written consent to participate in the LFS Screening Study and verbal consent for all family interviews. Interview transcripts were anonymized before analysis and participants were assigned pseudonyms. All data analysis files were stored on secure, password-protected NCI computer drives with access restricted to preapproved protocol investigators. This study was approved by the NIH IRB committee (clinicaltrials.gov #NCT01443468)

Data Analysis: Data Reduction and Reflexive Thematic Analysis

An interprofessional team with a social psychologist (COH), a genetic counselor (AST), and PhD-prepared licensed clinical social worker (AWL) conducted a secondary analysis of family interview data to explore social influence among siblings. Family interviews did not specifically ask about social influence among siblings, but participants spontaneously discussed these experiences when responding to questions about family communication, risk management, and decision-making. Although other family members were sometimes present, only content related to sibling and sibling-in-law relationships was included in analysis. The family group in each interview served as the unit of analysis. For the three sibling groups who completed multiple interviews, transcripts were combined into a single case file for analysis.

We used reflexive thematic analysis, supplemented with a codebook, to generate findings relevant to social influence and family practice (Braun, et al., 2019; Braun & Clarke, 2023). The data reduction (or coding) process consisted of first developing a working codebook with codes and definitions. The codebook was developed by (COH) and (AWL) based on the open coding of three randomly selected transcripts and included both inductive codes derived directly from interview content and deductive codes from previous literature (Saldaña, 2009) on social influence among relationship partners (e.g., Huelsnitz et al., 2022). The definition of social influence (intentional attempts by an agent to change a recipient’s health beliefs and/or behavior to be consistent with what the agent desires, Huelsnitz et al., 2022) informed deductive coding. Participant responses were coded as “social influence” if they were relevant to LFS, referenced one or more siblings, and explicitly or implicitly indicated preferences, opinions, or goals of the agent.

The codebook was further refined by applying it to an additional three transcripts by (COH) and (AST) separately, who then met with the senior qualitative expert (AWL) to review coding and revise the codebook. In addition to social influence and its subcodes, including general social influence, explicit/direct influence, and implicit/indirect influence, the final codebook consisted of four additional domains with these core components: interdependence, reorganization of family roles, social support, and self-versus-other emotions (see Table 1). These codes were derived from our research questions and relational theories theoretically linked to social influence, including self-determination theory (Ryan & Deci, 2017), interdependence theory (e.g., Agnew et al., 1998), social control (e.g., Lewis & Butterfield, 2005), and family systems theories related to chronic illness (e.g., McDaniel et al., 2014). Data reduction was completed once (COH) coded all 16 sibling-inclusive transcripts using the finalized codebook and secondary coders (AWL and AST) reviewed coding decisions.

Table 1.

Codebook Domains, Domain Definitions, and Sub-codes

Code	Sub-Codes and Definition(s)
Interdependence	Cognitive Interdependence: Captures ways in which siblings use collective versus individualistic language when referencing the beliefs, behaviors, emotions, or identity of the siblings/family. Text is linked to a shared belief system, identity, experience, etc. rather than just a casual use of “we” or “I.” Emotional Interdependence: Captures the extent to which siblings’ emotions are related to the emotions of each other. Includes expression of emotions from one sibling that are due to another sibling’s experiences. Behavioral Interdependence: This code captures ways siblings have opportunities to influence each other. This code does not actually capture social influence, but rather the extent to which siblings’ lives are entangled together (or not) in ways that reflect interdependence.
Reorganization of Family Roles	Reflects ways in which family roles have (re) organized (due to LFS or other family changes) that result in individual(s) taking on additional responsibilities or relinquishing responsibilities, such as caregiving, management of family communication, initiation of family gatherings/social events, maintenance of familial relationships, and management of healthcare.
Social Influence	General Social Influence: Captures range of ways in which siblings influence each other (or not) in the context of LFS and health more broadly. This code also captures beliefs siblings have about influencing each other, tensions between siblings when there is disagreement about how acceptable it is to attempt to influence each other and ambivalence towards influencing siblings. Also extends to influence from generational peers (e.g., cousins). Explicit/direct influence: Captures influence between siblings and/or generational peers that is explicit and direct. Examples include attempts to persuade, demands, requests, discussion, etc. Implicit/indirect influence: Captures influence between siblings and/or generational peers that is implicit and/or indirect. Examples include making hints, making environmental changes, showing opinions through emotions without directly confronting the topic, and modeling the behavior.
Social Support	Captures ways in which siblings support each other (or not). Could include making changes to one’s own behaviors to support LFS risk management efforts of siblings. Can be aspirational (i.e., support siblings hope to provide, hope others will provide).
Self vs. Other Emotions	Captures feelings that are expressed for sibling’s experiences but not one’s own.

Reflexive theme development consisted of focused thematic and axial coding to group codes based on implicit meaning (Strauss & Corbin, 1998; Braun & Clarke, 2023). This was facilitated by reflexive writing in the form of generating codebook domain summaries and then exploring central concepts that unite disparate coded data. Finalized themes represent latent meanings (i.e., implicit and conceptual) of social influence among siblings with LFS.

Trustworthiness and Rigor

Detailed audit trails during data collection and analysis boosted dependability and confirmability of findings. Prolonged exposure to participant families over many years and ongoing interprofessional case collaboration supported credibility (Patton, 1999). All members of the research team maintained reflexive practice to bolster consideration of positionality and manage bias (Olmos-Vega, et al., 2023) regarding organically derived themes (Srivastava & Hopwood, 2009). All conceptual work was supervised by a qualitative methodologist with expertise in familial cancer.

Results

Overview of Social Influence Characteristics

In 15 of the 16 interviews, siblings reported using direct and/or indirect forms of social influence in their families, and most identified instances of using social influence tactics with their siblings. In some interviews, participants openly and directly described family norms related to influence and/or ways in which they tried to shape each other’s behavior. In other interviews, participants described instances in which they tried to shape their sibling’s beliefs or behavior, but did not identify those actions as influence.² In one interview, siblings did not describe any instances of influence, either indicated by the participants (e.g., “I tried to get my sibling to engage in genetic testing”) or identified by the analytic team. Domains of LFS-related social influence included decision-making regarding genetic testing for oneself and/or cascade testing for one’s child(ren), cancer treatment decisions, reproductive behaviors, health behaviors (e.g., physical activity, tobacco use), screening participation, and risk-reducing surgeries. Most participants reported engaging in influence attempts in at least one domain.

Attitudes Toward Social Influence

Participants described social influence in terms of how much siblings respected each other’s freedom of choice, whether through attitudes or behaviors that showed this respect. Several participants indicated that they (or absent siblings) respected the autonomy of their siblings’ decision-making and therefore did not try to influence one another. Sisters Norma (age 30-39) and Annie (age 40-49) described how family members did not pressure each other to get tested.

Norma: It’s a personal decision, period. And I think it’s a healthy approach. I don’t believe anybody would -

Annie: Pressure to, or not to, get tested.

Similarly, after being asked about her reaction to her sister’s choice not to test her son for LFS, Marisol (age 30-39) said that it’s “her (sister’s) problem” and that she’s not going to “make” her sister test her nephew. Brothers Sherman (age 20-29) and Fred (age 20-29) described the absence of influence in their relationship:

Fred: It’s not like I’m pressured, “Hey…you really need to be doing this.”

Sherman: Not even a reminder. It’s not even, “Hey, have you done that?”

In Fred and Sherman’s family, each decision regarding LFS risk management (e.g., participating in cancer screening) was believed to be completely personal.

Three participant responses included mixed attitudes towards social influence. Jane (age 40-49) described a conversation with her sister-in-law in which she encouraged consideration of assisted reproductive technologies. Jane’s sister-in-law chose not to follow Jane’s recommendation.

Jane: And I know before they got pregnant…[my sister] and I both talked to this sister-in-law. Said, “You know, had we known that technology – it wasn’t available [for us] at the time. If it had been, we would’ve used it. To make sure we stopped. That it – we didn’t put our kids through this.”…I’ve never had that conversation with her again. I don’t hold it against (her). She doesn’t hold it against me. It was just a discussion. I gave her a perspective as a mom with kids who are affected [with LFS], that if I could’ve done something to prevent it, I would have.

Jane provided unsolicited information to her sister-in-law that implicitly intended to inform her sister-in-law’s reproductive decision-making. Although this influence attempt could have negatively influenced Jane’s relationship with her sister-in-law, Jane’s reflection indicated that the conversation was acceptable and fit within their relationship’s norms.

Vita (age 50-59) described respect for autonomous decision-making with her siblings while also acknowledging that she engages in influence by “nagging:”

Vita: …I think we make independent decisions. I wouldn’t presume to tell you, “Oh, you must get your knee replaced,” for example. That is for you to decide. I might nag you a little bit about certain things (laughter).

Additionally, Caroline (age 40-49) reported she would never tell her sister to pursue preventive mastectomy but that she would “not let her stop screening.” Overall, most participant responses described respect for their sibling’s autonomous decision-making, with a few participants providing mixed views.

Reasons for Presence and Absence of Social Influence

Participants described multiple factors that prompted or relieved them of the perceived need for social influence among siblings. Participants described weighing the potential relational costs against the potential health benefits. Most interviews included contextual information suggesting why social influence did or did not take place.

Facilitators

Facilitators of influence included the perceptions regarding severity of the consequences of the targeted health issue (e.g., passing on LFS to one’s children, a late-stage diagnosis), perceived lack of knowledge of the recipient, recipient denial, benefits of behavior change for the recipient, the perceived need for regulation/influence of the behavior/issue, and request for influence from another family member. Brother Randolf (age 60-69) and sister Vita (age 50-59) shared how their deceased brother was uninterested in discussing treatment options for prostate cancer prior to his death despite Randolf’s efforts to convince him to consider anti-androgens.

Randolf: …he would say it would “turn him into a girly man” and he would rather die. “Well, you may get your wish because this is a hormone-sensitive variant of prostate cancer, and your testosterone is still high, and your PSA is high.” And he wouldn’t even read up on that because he didn’t want to go there.

In his attempt to influence his brother, Randolf expressed the severity of the potential consequences (i.e., death), highlighting how siblings may feel compelled to enact social influence even when it is unwanted.

In contrast, Jane (age 40-49) indicated that she engaged in social influence for her brother when requested:

Jane: My sister-in-law will call me and say, “Jane, your brother is supposed to have his colonoscopy; he still hasn’t. Can you call him?” So, big sister pressure…It’s not my place to interfere unless she asks me. And then I just tease him [and] say, “You really need to do this for your wife. She’s worried.” Then he’ll do it. But I only do it if I’m asked.

Jane reinforced the consequences of her brother’s reluctance to undergo colorectal cancer screening in terms of the negative feelings it caused his wife, but did not indicate whether she, herself, was worried about her brother.

Caroline’s (age 40-49) sisters identified her as the family leader regarding LFS management. She reported the benefits of risk management as a reason for attempting social influence: “…if they were doing [cancer screening] and I knew that they were doing a good job, then I could relax a little bit.” Caroline implies that influence is unnecessary when family members share views on the importance, and actively engaged in, the target health behavior.

Absence of Need

Participants implicitly stated reasons for refraining from influencing siblings. Some participants described alignment in beliefs or that their sibling was engaging in what would otherwise be the targeted behavior for influence, thus eliminating the perceived need for influence.

A few sibling pairs indicated that parents or other family members engaged in social influence (e.g., scheduling appointments, prompting individuals to pursue genetic testing), which relieved siblings of that responsibility. Michelle (age 50-59), for example, in her role as parental and behavioral guide relieved her young adult children, Buck (age 20-29) and Lindsey (age 20-29), of these tasks:

Interviewer: And mom follows-up with you guys, if there’s needed follow-up about the study? How does that generally work?

Buck: Oh, yeah…like, “you need to get your labs done by this date. So, bring your medical card and I.D. and go get it done.”

Michelle: He’s really good. Buck goes within 24 hours. Lindsey’s really bad. We have to actually drive out of town, pick her up, and drive her to get her to go. She won’t do it unless we’re there.

The interviewer later asked, “Do you guys check in on one another? I mean, like are you eating your vegetables? How do you guys communicate about that stuff?” Lindsey responded, “It’s really just mom.” Such patterns may shift with age or following the death of a parent to an LFS-related cancer. Similarly, brothers George (age 20-29) and Frank (age 15-19) discussed how their mother helped them to manage the multiple aspects of the LFS study screening protocol. In interviews in which siblings described parental influence attempts, the participant siblings were in their late teens or early twenties.

Forms of Social Influence Among Siblings

Twenty-one participants (72%) described 34 instances of social influence attempts. Of these, in 21 instances the participant was an agent of influence (i.e. tried to influence their sibling) and in 13 instances the participant was a recipient of influence (i.e., a sibling tried to influence the participant). Participants described social influence strategies that varied in directness and the degree to which they supported or limited autonomy.

Directness

Several participants described direct social influence strategies that targeted health behavior openly, clearly, and explicitly. These included asking or reminding the recipient to change or take action, reasoning logically with the recipient, stating the importance of the target behavior, discussing the situation, offering to make the desired change together, and framing the recipient’s health behavior as a family responsibility. Caroline (age 40-49) reported using direct strategies across multiple domains. When asked by the interviewer how family members chose to participate in the LFS screening study, Caroline said, “I just demanded they go…I called them, and I told them to come.” She later stated, “I told them they had to get tested, and they did.”

Most of the siblings who reported direct forms of influence, like Caroline, reported asking or demanding specific LFS-related actions. Briana (age 30-39) said, “I’m pushing this one [brother, Jerry, age 40-49, present in interview], I’m like, ‘You’ve got to get your scans.’” Katie mentioned telling her family members (including siblings) not to eat on plastic tableware, noting possible carcinogenic effects. Overall, direct influence ranged in intensity, from demanding, pushing, or challenging, to asking or telling. Some forms of influence appeared to be indirect, such as expressing emotions, making suggestions, dropping hints, using humor/joking, trying to involve other people in the influence process, or praising or complimenting the recipient. Indirect attempts at social influence were less specific, such that the agent’s goals were apparent, but the means were inferred. Several participants described reciprocal forms of indirect influence. In one family, with brother Charles (age 50-59) and sisters Ruth (age 60-69) and Kerry (age 50-59), Charles described quitting smoking and his reasons for doing so, such as having difficulty breathing while cycling and the financial costs. His sisters chimed in:

Ruth: And it made his mother happy.

Kerry: Made your sister happy.

Ruth: But that wasn’t his motivation. That was just a side effect.

Charles: They’re off my ass a little bit.

While Ruth and Kerry denied that their approval motivated Charles’ change, they both expressed positive emotions in response to Charles’ smoking cessation as a form of cancer risk management. In this example, the group engaged indirect influence by acknowledging their happiness with Charles’ behavior change. Similarly, in reference to her brother, Jerry (age 40-49), Briana (age 30-39) described how her “mother and everybody else will be happy now that he’s getting his scans.”

Another form of indirect influence, reported by several individuals, included providing information and/or resources to engage in the agent’s desired behavior, but giving the recipient space and patience to make the change themselves. Sherman (age 20-29) described an indirect influence attempt with his untested sister:

Sherman: I don’t think there’s real pressure. Like, I gave her the kit and stuff to do it and, like, ‘whenever you want to get it done, it’s ready to go.’ And we’ve asked her, “Are you going to do it?” But I don’t think there’s any pressure to get it done.

Here, Sherman explicitly stated his goal was not to induce pressure but rather to reduce barriers to a given target behavior. However, given that Sherman said he gave her the testing kit, surveilled her behavior, and followed up with her by asking if she is going to get tested, Sherman’s behavior is indicative of intentional influence towards a goal (for his sister to get tested).

Autonomy-Supportive versus Autonomy-Limiting Influence

Nearly all participants described occurrences of autonomy-supportive influence that bolstered a sibling’s self-determination and expanded the sibling’s choices regarding a given health behavior. Importantly, behaviors were considered autonomy-supportive if an agent’s goal for changing a sibling’s beliefs or behaviors was implied or explicit – if it was unclear whether the agent intended to change the sibling’s beliefs or behaviors, the behaviors were not coded as social influence. Most individuals who described autonomy-supportive forms of influence described providing information and support to their siblings in various decision-making contexts. For instance, Vita (age 50-59) described trying to help her sister, Rebecca, complete cascade testing for LFS, “I was focusing more on, ‘Rebecca, let’s get your paperwork in, Rebecca, let’s get this done, and we did so I’m hoping she will get tested.” Vita indicated she had a goal for her sister (cascade testing), and she engaged in actions intended to support her sister’s move towards that goal.

Michelle (age 50-59) described her sister as a “food Nazi” referring to her sister’s beliefs regarding eating primarily plant-based diets and engaging in exercise for cancer prevention. The interviewer asked whether Michelle’s sister “pushes those ideas.” Michelle responded saying, “No, she talks to us about it, and it’s hard to say she’s not correct. But she doesn’t push it, she encourages it.” Michelle was familiar with her sister’s beliefs about diet and exercise and indicated that she intended to change her health behavior for the purpose of reducing cancer risk. Michelle also indicated that her sister encouraged eating a plant-based diet and exercising. Thus, Michelle’s sister engaged in autonomy-supportive influence because she had a goal (to change her sister, Michelle’s, behavior) and engaged in a supportive way that focused on education and information-sharing.

Several participants described occurrences of autonomy-limiting influence, which constrained the recipient’s behavioral decisions or applied pressure on the recipient to think, feel, or behave in a specific way. Most of these occurrences were aligned with directive approaches, such as demanding or telling their sibling to engage in a specific health behavior.

In one interview with brothers Frank and George, George said that he did not participate in the LFS cancer screening study during the first year because he was unsure about it until Frank returned and reported it “was fine”. The interviewer then asked Frank how he reassured George.

Frank: I probably wouldn’t be the best for reassuring because the first year didn’t go great with the blood draw for me. It was one day worth of tests, just blood work, an interview, a physical, and then an MRI. It was difficult because we don’t have good veins. They tend to collapse…They were taking a lot of vials. It took a while.

Interviewer: That’s no good. Did you tell him about that?

Frank: No, not in detail.

Interviewer: You didn’t want to scare him?

Frank: Mm-hmm.

By withholding negative information about the experience from George, Frank limited George’s autonomy and ability to make a fully informed decision because Frank, presumably, wanted George to participate in cancer screening. This example highlighted the value of knowing individuals’ motivations to strengthen the impact of influence amongst their siblings.

Finally, sister dyad Annie (age 40-49) and Norma (age 30-39) described a substantial disagreement regarding treatment decisions:

Annie: I wanted a preventative mastectomy. She told me I was crazy.

Norma: No, I didn’t say you were crazy. That’s a huge deal, and you can take your time with that decision, and be 100 percent sure.

Annie: It was boobs.

Norma: I would accept that decision. I never said you’re crazy, but I also said, with our disease, you would cut off your bones, your brain, your blood, your everything. So, that’s my only concern, is where do you draw the line on the stress it’s causing? I’m not a doctor, and I’m not you. That’s your decision, I would have supported you – well, you know now.

Annie described criticism and disapproval as an autonomy-limiting form of influence: being called “crazy” by her sister. Norma refuted this claim, stating support for Annie’s autonomous decision-making and emphasizing that she wanted Annie to have all the information to make the best possible informed decision. This highlighted how agents and recipients of influence can have different perceptions of the influence strategies and motivations.

Discussion

Sibling relationships are long-lasting bonds, often characterized by psychological closeness, interdependence, and a high degree of knowledge about one another. Consequently, siblings may engage in social influence across a variety of domains to extend quality of life and longevity for each other. Siblings with LFS share both health and relational risks. Throughout their siblingship they share a family health history and high genetic cancer risk while also sharing the possibility of losing loved ones, and each other, to cancer. Under the shadow of a serious health threat of LFS, siblings may be motivated to engage in social influence attempts to encourage genetic testing, prevention, screening, and treatment behaviors. Consistent with these ideas, we observed that siblings reported using social influence across LFS-relevant domains, while also noting that siblings hold diverse attitudes about the relational appropriateness of using social influence. Additionally, this research found varied reasons for the presence or absence of social influence; for instance, siblings may cede social influence to important others (e.g., parents), potentially based on developmental readiness. This research also found that siblings reported multiple social influence attempts and a variety of influence strategies.

Self-Determination Theory (SDT) and Sibling Influence

This study utilized self-determination theory (SDT) to frame sibling influence in the context of LFS. SDT emphasizes the importance of autonomy in the context of important relationships – specifically, the role of close others in either supporting or undermining an individual’s sense of autonomy (Ryan & Deci, 2017). Research has consistently shown that autonomy support is linked to positive health and well-being outcomes (e.g., Gillison et al., 2019; Slemp et al., 2024). However, relatively few studies have examined autonomy-supportive and autonomy-limiting influence behaviors within adult sibling relationships, particularly in shared high-risk health contexts like LFS. SDT posits that autonomy support can be especially important in situations where individuals face constraints on their autonomy, such as the health risks associated with LFS.

Our findings align with SDT in that siblings expressed appreciation for autonomous decision-making in their relationships. Participants described respecting their siblings’ decisions, with many explicitly noting their efforts to avoid exerting familial pressure related to LFS risk management. This is a clear manifestation of autonomy support, where siblings facilitate each other’s decision-making processes without imposing undue control or pressure.

However, we also found evidence of mixed attitudes toward influence, such that several individuals simultaneously indicated respect for their siblings’ independent decision-making while also reporting attempts to influence sibling beliefs or behavior (typically using autonomy-supporting strategies). This ambivalence may reflect Western cultural attitudes that value individual autonomy in healthcare decision-making and show aversion toward controlling or regulating one’s close others. Indeed, in several instances participants acknowledged their attempts to influence their siblings but provided justifications for doing so, such as being asked to by another close family member, caring about their sibling, or considering severe consequences for the sibling of not engaging in the behavior change (e.g., late-stage cancer diagnosis or cancer-related death). Few studies have examined individuals’ attitudes toward influence among close others. The current study suggests that while individuals with LFS may view social influence with some ambivalence, they are more approving of autonomy-supportive strategies than those that inhibit autonomy. Nonetheless, given the high stakes of living with a shared, multi-organ cancer risk, siblings may still attempt to influence each other’s health decisions, even when influence is perceived as a complex or sensitive dynamic.

Motivations for Social Influence Presence and Absence

Participants indicated a variety of reasons for the presence and absence of social influence in sibling relationships. Consistent with past research (e.g., Lewis & Butterfield, 2005), participants evoked negative consequences of their sibling not engaging in the desired behavior change (e.g., passing on LFS to one’s children, late-stage cancer diagnosis, death). In some families with young adult siblings, parents or other family members engaged in social influence, relieving siblings of these roles. Parental influences on LFS decision-making may lessen as individuals transition from adolescence into young adulthood and siblings may play a greater role in influencing each other. Additionally, in some sibling groups, one sibling was identified (implicitly or explicitly) as the main influencer (e.g., Caroline). For some individuals, this role designation may be based on sibling dynamics that were shaped in childhood or adolescence (e.g., Fishbane, 2019), whereas for other families, these roles may have been based on changes over time to the family structure, including changes that may result from cancer-related events. Future research could examine how changes to the family structure in families with LFS, due to caregiving, diagnosis, or death, affect which individuals engage in influence attempts. Further, responses to social influence may correspond to perceptions of the utility of the target behavior; attempts at social influence may be more positively received and attended to when they align with the recipients understanding and agreement about the utility of the target of change.

Autonomy-Supportive and Autonomy-Limiting Strategies in Sibling Influence

The strategies siblings use to influence each other also reflect key principles of SDT. Most influence attempts in this study were autonomy-supportive and direct, such as discussing a recipient’s approaches to LFS management and sharing information that broadened potential cancer risk management options. SDT theorizes that autonomy-supportive strategies are more likely to lead to self-directed behavior change because they promote feelings of competence in the decision-making process (Ryan & Deci, 2017).

Participants shared only a few instances of autonomy-limiting and indirect strategies of social influence. While rare in the current study, these strategies, such as indirect pressure or coercion, can be perceived as controlling, potentially leading to reduced motivation for the recipient. SDT suggests that when individuals feel their decision-making is controlled by others, their sense of autonomy is undermined, leading to negative emotional outcomes. The few instances of autonomy-limiting behavior could reflect a social desirability effect, where participants hesitated to report controlling behaviors in an interview setting (both in terms of the behaviors they engaged in, as well as the behaviors their sibling(s) engaged in). Alternatively, it may indicate that these strategies are less common in family groups that value autonomy.

Strengths and Limitations

These data are derived from the largest longitudinal interview study of families with LFS. Some families completed more than one interview within the data collection period. Additional strengths of the study include the wide age range of participants and diversity in the sibling relationships represented (e.g., sister-sister dyads, brother-sister dyads, brother-brother dyads, sibling triads). The sample was relatively homogenous with respect to race and ethnicity, and thus we are limited in making inferences about how aspects such as cultural context may affect social influence processes. For instance, research has shown that people from certain cultural backgrounds (e.g., Asians, Asian Americans) may benefit more from indirect rather than direct interpersonal support (Kim et al., 2008). This may be true with health-related social influence. Additionally, the sample included participants who were engaged in genetic research, testing, and preventive screening, suggesting the possibility of a self-report bias and limited interpretive strength regarding reports on attitudes and behavior of siblings who did not participate. Relatedly, this study used an exploratory, family discourse research design, rather than a dyadic sibling design; the latter could address research aims related to concordance of sibling beliefs and behaviors related to LFS.

Data were collected between 8-13 years prior to this analysis; though recommended health behaviors and risk management strategies have not largely changed in that time, information is more widely available, reducing burden on siblings to share hard-to-find information and providing individuals with LFS with greater supports in conversations with loved ones. Our analysis focused on relational processes (e.g., influence), which may be more stable in family groups across time. Finally, although interviewing families together can elucidate family dynamics in rich and interesting ways, it is possible that some siblings present in family group interviews did not fully express their thoughts and feelings due to the presence of others. For instance, van Oostrom and colleagues (2007) found that, in the context of Lynch syndrome, siblings who tested negative felt guilty towards siblings with pathogenic variants, which could affect what they disclose in a shared interview.

Clinical Implications and Future Directions

Social influence among siblings with LFS may be a potent avenue for increasing family cascade testing and participation in cancer risk management, and thus reducing morbidity and mortality (e.g., Roberts et al., 2018). Social influence may be key to understanding why cascade testing interventions sometimes show small effects on genetic testing uptake (Baroutsou et al., 2021). However, given our limited understanding of the consequences of social influence processes for relationships and individuals, additional work is needed before social influence interventions may be responsibly implemented in clinical contexts. Future work might examine multiple perspectives on social influence, including both the siblings engaging in influence (i.e., agents) and siblings being targeted for influence (i.e., recipients), or the reciprocal nature of such influence. Such work might focus on the agents’ intentions and influence strategies, the recipients’ perceptions and interpretations of agents’ influence strategies, and recipients’ relationship-relevant and health-relevant responses. Discordance between siblings with respect to beliefs and behaviors in negotiating decision-making and plans for genetic testing, cancer prevention, and treatment may predict social influence attempts and impacts on health and relationship outcomes.

Research suggests that, in some contexts, autonomy-supportive influence strategies have positive effects on health and relationship outcomes, whereas autonomy-limiting strategies have null or negative effects (e.g., Huelsnitz et al., 2022). However, most of this work has been limited to romantic relationships and investigators have identified the need to consider both the effects of the quality of interactions with romantic partners and the quality of interactions with family members to understand the role of relationships for physical health (e.g., Woods et al., 2014). Future work must ensure the benefits of sibling influence outweigh the costs before recommending that siblings engage in influence processes with one another. Such work might examine the nature of how influence is exerted by the actor and experienced by the recipient, and the social influence exerted by the researcher during data collection. For instance, the nature of some siblings may yield latitude for varied and repeated attempts at influence from one another due to their shared cancer risk and shared family histories of illness and loss.

Conclusion

In a healthcare system that predominantly places behavior change efforts at the individual level, the influence of close others on individuals’ health is an understudied, yet potentially powerful means for attitudinal and behavioral change. The current study contributes to our understanding of health behavior change by showing that, in the context of a heritable cancer predisposition syndrome, siblings report engaging in a variety of influence strategies, for various reasons, across multiple health domains. These relational processes may have clinical implications, by which health and mental health clinicians may leverage social influence to improve outcomes for individuals and families.

Data Availability Statement

De-identified data will be shared with qualified investigators after IRB review and establishment of appropriate data transfer agreements. Please contact the corresponding author for data requests.