Participatory development and feasibility study of a digital intervention for detecting and treating bio-psycho-social needs of long-term cancer survivors: study protocol of the DELPHIN study

Abstract

Introduction

Long-term cancer survivors may suffer from significant bio-psycho-social burden even years after treatment. Yet, a structured approach to detect and address bio-psycho-social burden of long-term cancer survivors in primary care is missing in Germany, although family physicians are the primary medical contact for most patients. In this paper, we describe the DELPHIN study aiming to develop and test a structured care model for long-term cancer survivors. The DELPHIN study and intervention will facilitate networking of regional medical and non-medical services. This protocol describes the intervention as well as the pilot study.

Methods

The DELPHIN study comprises a developmental and a feasibility phase. In the developmental phase, we will assess (1) the current care needs of long-term cancer survivors (n=1000) using a cross-sectional questionnaire survey; (2) in an additional cross-sectional questionnaire survey, we will address medical and non-medical care providers to assess current care practice for this patient group (n≥250); (3) a qualitative interview study with both long-term cancer survivors (n=12) and family physicians (n=10) will assess patients’ needs and barriers for effective care. Results will then be triangulated to inform development of the DELPHIN intervention. The intervention shall include the following elements: the DELPHIN mobile app for patients with a digital screening tool, a digital treatment plan, a survivorship passport and information on regional medical and non-medical providers. Additionally, a DELPHIN website and a DELPHIN eLearning tool for family physicians will be developed. The subsequent feasibility study will follow 100 long-term cancer survivors using the DELPHIN app for 4 months, with two assessments (t⁰=baseline; t¹=4 months follow-up) regarding the usability of the app and their health-related quality of life. The eLearning tool will be tested by 50 family physicians using three measurement points to evaluate learning success (t^a=before; t^b=directly after eLearning; t^c=after 4 weeks).

Discussion

The DELPHIN study seeks to address cancer survivors’ unmet bio-psycho-social needs through implementing a digital mobile application. Positive results in the feasibility study will provide the basis for a future effectiveness study and integration into routine care.

Ethics and dissemination

The study was reviewed by the Ethics Committee of the University of Bonn, Germany (No: 2024-409 BO) which did not object to the study.

Trial registration number

DRKS00035726.

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• The DELPHIN study addresses bio-psycho-social needs of long-term cancer survivors regardless of entity by building on existing structures using a digital tool.

• The DELPHIN study focuses on long-term cancer survivors in the primary care setting and their family physician as key coordinators of long-term care.

• The methodology integrates a longitudinal mixed-method approach to develop and test the intervention.

• A participatory approach guarantees relevance and practicability.

• Using digital tools for the DELPHIN study, long-term cancer survivors with limited technical literacy may be underrepresented in the study population.

Introduction

In Germany, around 500 000 individuals are newly diagnosed with cancer every year.¹ By 2040, the number of new cancer cases might even double, partly due to increasing longevity in modern societies.² Improved cancer therapy has decreased the estimated number of cancer deaths in Europe between 2018 and 2023 (men: −6.5%, women: −3.7%³), and the relative 10-year survival rate across all cancers is currently around 60%.¹ In Germany, there are currently around 5 million individuals living with or after cancer treatment.⁴ Around 2.6 million of these were diagnosed with cancer five or more years ago,⁵ who are called long-term cancer survivors. More than a third of these still consider themselves to be ‘patients with cancer 5 to 15 years after diagnosis.⁶

A significant number of long-term cancer survivors are still experiencing considerable long-term and late effects, even though modern treatment options have become more tolerable.^{7 8} By definition, long-term effects begin during acute therapy and can last for years.^{9 10} In contrast, late effects occur months or even years after the end of cancer therapy. Frequent long-term side effects and late effects can be categorised using a bio-psycho-social grid and include, among many other topics: cardiovascular diseases, secondary malignancies (second tumours), infertility, depression, psychosomatic exhaustion, fear of recurrence and progression, occupational problems, financial problems, relationship and network problems.¹¹ The population-based CAESAR+study (2009–2014) examined 6952 cancer survivors after breast, colorectal and prostate cancer in Germany. It showed that their general quality of life was insufficient with deficits in cognitive, emotional, physical and social functionality compared with the general population. Common complaints are sleep disorders, fatigue, dyspnoea, gastrointestinal disorders and financial difficulties.¹² Fatigue is one of the most common side effects with persistent symptoms in around 30% of all patients.¹³ Clinically relevant psychosocial distress was found in about 20% of all colorectal cancer survivors, with impact on their care needs regarding employment, legal services, finances and relationships.¹⁴ Similarly, about 15% of Canadian head and neck cancer survivors reported unmet needs in social problems.¹⁵ Bio-psycho-social burden persists up to 15 years in cancer survivors.¹²

Cancer survivors encompass heterogeneous courses of disease, requiring patient-specific evaluation of needs and intervention strategies.¹⁶ The individual risk of long-term and late effects depends on, among other things, the type of cancer, the cancer treatment and other factors such as genetic predisposition, age and social environment.¹⁷ Around one-third of long-term survivors are of working age, while around 40% are aged 75 or older. Although children, adolescents and young adults make up a minority of patients with cancer, they are at especially high risk of long-term and late effects including psycho-social impairments.¹⁸ Yet, there is no comprehensive analysis of the care situation of cancer survivors in Germany that reflects the reality of care across cancer types, patient groups and sectors.

A previous study of 456 long-term cancer survivors after breast cancer in Germany found that family physicians are directly involved in cancer-specific follow-up care for up to 20% of the participants.¹⁹ In another qualitative study with 38 US family physicians, they considered themselves crucial healthcare providers for long-term cancer survivors by providing ‘whole person care’.²⁰ Nevertheless, integrated care solutions for long-term cancer survivors led by family doctors are still lacking in Germany, although the family physician setting with its person-centred, longitudinal approach might be particularly suitable for supporting this heterogeneous patient group.

The DELPHIN study aims to develop a digital system to address various bio-psycho-social care needs of long-term cancer survivors across all cancer types. Since family physicians play a pivotal role in their long-term survivorship follow-up, their systematic involvement can contribute to comprehensive and coordinated survivorship care. By building on existing networks, we aim to improve the networking of existing structures and increase access to medical and non-medical services. This approach avoids the creation of new, potentially expensive structures by using resources that are already in place. In this paper, we will

1. Describe the developmental process and content of the DELPHIN intervention.

2. Describe the methods of the feasibility study of the DELPHIN intervention.

Methods and analysis

The study was reviewed by the Ethics Committee of the University of Bonn, Germany (No: 2024-409 BO) which did not object to the study. The DELPHIN study is registered in the German Register of Clinical Trials (DRKS00035726). This study protocol was prepared according to the SPIRIT checklist.²¹ The filled-out checklist can be found in online supplemental material 1.

Intervention

As part of the DELPHIN study, we will develop the components as well as their contents, and test the DELPHIN intervention for long-term cancer survivors in the primary care setting. The DELPHIN intervention is conceptualised as a multimodal and participatory framework and aims to support long-term cancer survivors by addressing their various bio-psycho-social needs sufficiently within the German healthcare system. The DELPHIN intervention will consist of the following components:

• DELPHIN screening tool for patients.

• DELPHIN treatment plan and survivorship passport.

• DELPHIN website and DELPHIN app with information on regionally available services for bio-psycho-social needs and psychoeducational content for long-term cancer survivors.

• DELPHIN eLearning for family physicians and medical assistants.

In detail, included patients will use the digital screening tool for bio-psycho-social needs via the DELPHIN app. The results will display the current care needs of the users. Afterwards, patients will have two options:

1. The current care needs will be linked to contact data of local medical and non-medical services that might address these needs. Patients will receive contact details and details about the service.

2. If patients feel unsure about their care needs and might want to consult their personal family physicians, they can jointly determine appropriate actions. For this purpose, we will provide a template of a bio-psycho-social treatment plan as well as a survivorship passport via the DELPHIN app.

Furthermore, both long-term cancer survivors and family physicians will have access to a website that displays locally available services in the medical and non-medical fields.

To support family physicians in their care provision for long-term cancer survivors, we will develop an eLearning tool to inform about care needs and the possibilities to address them within the German healthcare and social system. Figure 1 shows an overview of the DELPHIN intervention.

Figure 1. Contents of the DELPHIN intervention.

Design of the DELPHIN study

The DELPHIN study follows a sequential mixed-methods design to both develop and pilot the DELPHIN intervention as proposed by the literature²² . It is divided into a developmental and a feasibility phase. Both parts of the study use a mixed-methods approach to investigate the care needs of long-term cancer survivors from different perspectives. An overview is given in figure 2.

Figure 2. Design of the DELPHIN study.

Developmental phase

The developmental phase aims to gather evidence for the contents of the planned components of the DELPHIN intervention. It comprises three different sub-studies to assess needs and barriers to care of long-term cancer survivors. Furthermore, the participatory development of the contents will be described here. Overall, the developmental phase aims to assess current burden, care needs and barriers to comprehensive long-term cancer care in the German primary care system.

Cross-sectional survey with cancer survivors

We will conduct a quantitative cross-sectional survey to assess the current physical, psychological and social care needs of long-term cancer survivors in the primary care setting. Using an adapted version of the distress thermometer of the National Comprehensive Cancer Network (NCCN distress thermometer),²³ care needs will be assessed. We will not only evaluate if patients have current care needs but also whether they think these needs are related to their cancer. Additionally, we will assess their current health status, the care they have received previously, as well as their quality of life and other patient-reported outcomes. All outcomes and their respective operationalisations are listed in table 2. The survey will be issued using an initial pilot version of the DELPHIN app, which is designed exclusively for needs assessment and will subsequently be further developed.

Cross-sectional survey with medical and non-medical providers

We will survey family physicians as well as other medical and non-medical healthcare and social care providers about their current care for long-term cancer survivors. Physicians included will be family doctors as well as oncology-related specialists. Non-medical providers are inter alia physiotherapists and occupational therapists, but also debt advisors, social advisors, etc. We will contact potentially eligible providers based on public information. The choice of providers is based on the international literature and clinical experience by the research team. We will assess if providers offer special consultation to long-term cancer survivors, if the target patient groups uses it and what barriers they face in providing care. Data will be assessed using the online tool UniPark, which is in line with all applicable data protection regulations. Table 1 shows an overview of all medical and non-medical providers that shall be approached in the cross-sectional survey. All outcome measures are shown in table 2.

Table 1. Medical and non-medical providers in the developmental phase.

Category	Discipline
Medical providers	General practice/family medicine
	Oncology
	Gynaecology
	Urology
	Internal medicine (general, with a focus on pulmonology and gastroenterology)
	ENT (ear, nose and throat)
	Psychosomatic medicine/psychotherapy
	Psychiatry
	Pain management
	Chiropractic medicine
	Neurology
	General surgery
	Plastic surgery
	Cardiology
	Dentistry
	Rehabilitation medicine
	Ophthalmology
	Endocrinology
Non-medical providers	Physiotherapy
	Speech and language therapy
	Occupational therapy
	Osteopathy
	Nutritional counselling (with a focus on cancer)
	Cancer counselling centres
	Self-help groups and peer support circles
	Religious groups and support persons

Table 2. Outcome measures and measurement points.

		Cancer survivors			Family doctors and other providers
		Cross-sectional survey study	Feasibility study		Cross-sectional survey study	Feasibility study
			t0	t1		ta	tb	tc
Primary outcome—feasibility measures
Outcome	Instrument
Usability	G-MAUQ25			X			X
Mobile Rating	MARS26			X			X
Screening of psychosocial needs
Bio-psycho-social needs	NCCN Distress Thermometer23	X	X	X
Depression and anxiety	PHQ-437	X	X	X
List of secondary outcomes and confounders
Sociodemographic data	Study-specific, self-developed questionnaire	X	X		X	X
Cancer-related data	Study-specific, self-developed questionnaire	X	X
Subjective social status	MacArthur Scale38	X	X
Data on health behaviour	Study-specific, self-developed questionnaire	X	X
Health-related quality of life	Items of the EORTC library27	X	X	X
Current healthcare information	Study-specific, self-developed questionnaire	X	X
Fear of recurrence	FoP-Q-SF39	X	X	X
Technology acceptance	ATI scale40	X	X			X
Environmental quality of life	EQL scale41	X	X
Illness beliefs	B-IPQ42	X	X	X
Social identification	According to Häusser43	X	X	X
Data protection concerns	Study-specific, self-developed questionnaire			X
Details of the practice and care	Study-specific, self-developed questionnaire				X	X
Networking request	Study-specific, self-developed questionnaire				X	X
Desire for further training	Study-specific, self-developed questionnaire				X	X		X
Questions for the learning objective check	Study-specific, self-developed questionnaire					X	X	X

ATI, Affinity for technology interaction; B-IPQ, Brief Illness Perception Questionnaire; EORTC, European Organisation for Research and Treatment of Cancer; EQL, Environmental Quality of Life; FoP-Q-SF, Fear of Progression Questionnaire - short form; G-MAUQ25, German version of the mHealth App Usability Questionnaire; MARS, Mobile App Rating Scale; NCCN, National Comprehensive Cancer Network; PHQ-4, Patient Health Questionnaire - 4 ; t0, baseline; t1, follow up after 4 months; t1, follow up after 4 months; ta, baseline; tb, directly after eLearning; tc, follow up after 4 weeks.

Qualitative interviews with cancer survivors and family physicians

A qualitative interview study will assess patients’ needs and challenges of cancer survivorship care from both perspectives, patients and family physicians. Semi-structured interviews will be conducted via telephone or video meeting software. Interviews will be based on interview guidelines assessing current status of care, experiences and needs, and perceived risks along with proposed suggestions for care improvements. To compare interviews between patients and family physicians, interview guidelines will be developed iteratively in a piloting phase, comprising four pilot interviews (cancer survivors: n=2, family physicians: n=2). The interviews will be digitally recorded and transcribed verbatim.

Participatory development of the contents of the DELPHIN intervention

To develop the contents of the DELPHIN intervention, we will triangulate all previous results and transfer them into the digital components for patients and eLearning for physicians. Afterwards, all project members will be invited to give structured feedback on the content. An additional focus is laid on the feedback of patient representatives. Thus, a close collaboration of researchers, patients, family physicians and medical informatics specialists will realise the app and the eLearning.

Study 2: Feasibility phase

Pre-testing

After development of the contents of the DELPHIN intervention, we will have cognitive pre-test interviews with n=5 family doctors and n=5 long-term cancer survivors. Both target groups will test their respective components of the intervention and provide feedback on its usability, functions, content and overall comprehensibility. The pre-tests will be guided by a structured guideline and led by an experienced researcher. The pre-tests will be digitally recorded and transcribed verbatim. The results of the pre-tests will be incorporated into the app after each interview. Thus, each new pre-test will contribute to an improved version of the DELPHIN intervention.

Prospective feasibility study

The feasibility study is divided into two parts. First, the patient-sided intervention will be tested with at least n=100 long-term cancer survivors. This will be done in a 4 month longitudinal study with two measurement points: t⁰=baseline; t¹=follow up after 4 months. Furthermore, we will assess patient-reported outcomes analogous to the developmental study. This approach allows for preliminary insights into the effectiveness of the intervention. All data will be assessed via the DELPHIN app.

The eLearning tool will be tested by n=50 family doctors. A learning goal approach is used by assessing knowledge about the care needs of long-term cancer survivors and the respective care provision previous to the eLearning (t^a), directly conducting the eLearning (t^b) and again after 4 weeks (t^c). Additionally, we will assess feasibility measures. All data will be assessed via the online eLearning platform. All outcome measures are displayed in table 2.

Outcome measures

As we aim to test the DELPHIN intervention for feasibility, the primary outcomes are related to this and based on Pearson et al²⁴:

• Ease of use, user satisfaction and usefulness operationalised by the German version of the mHealth App Usability Questionnaire (G-MAUQ).²⁵

• Rating of mobile features operationalised by the Mobile App Rating Scale (MARS questionnaire).²⁶

The internal consistency of both the primary outcome measure (MARS) and the G-MAUQ was found to be good.^{25 26}

Furthermore, as the DELPHIN intervention aims to increase the health-related quality of life²⁷ of long-term cancer survivors, health-related quality of life is included as an additional outcome to generate preliminary evidence of effectiveness. Health-related quality of life is assessed using selected items from the item library of the Eurpean Organisation for Research and Treatment of Cancer (EORTC). We will further assess several patient-reported outcomes, which might explain the current care needs of long-term cancer survivors such as fear of recurrence, illness beliefs and health behaviour.

Table 2 shows an overview of all quantitative outcome and confounder measures assessed in the DELPHIN study and their respective measurement points. Most selected instruments and questionnaires are well established, validated and widely used within medical research. Where no suitable validated instruments were available, study-specific questions were developed.

Eligibility criteria

Inclusion criteria

1. Long-term cancer survivors: (1) Cancer diagnosis 5 or more years ago, (2) ≥18 years old, (3) sufficient knowledge of the German language and (4) use of smart device (tablet/mobile phone).

2. Family physicians: (1) Physician is certified as a family physician specialist or general internist, (2) practice treats long-term cancer survivors and (3) practice has internet access.

3. Other medical specialists and non-medical service providers: The provider offers a service that is, based on the international literature and expertise of the research team, linked to long-term cancer survivors.

Sample size and recruitment

Developmental phase

For recruitment of family doctors, non-medical service providers and patients, we will use a multimodal approach, aiming to address a broad spectrum of providers and patients with a wide range of cancer entities.

First, we will cooperate with a group of family physicians (n=20 practices) from the research network of the Institute for Family Medicine at the University of Bonn. These family doctors will recruit patients from their patient base to participate in Study 1. Physicians will receive 1000€ for their support in the study including participation in the interviews. Furthermore, we will recruit former patients from the Center of Integrated Oncology, University Hospital Bonn, and local self-help groups as well as through public advertisements. Overall, we plan to recruit a total of N=1000 patients. Patients from all four recruitment channels will receive a QR code with which they can access an initial version of the DELPHIN app. This initial version only contains the cross-sectional survey as part of the development phase. The study information and informed consent are integrated in the DELPHIN app.

As part of the informed consent form in the study, both the patients and the cooperating physicians are asked whether they are also willing to take part in interviews and/or pre-tests. Patients will receive 25€ for their participation in the interviews and pre-tests. We are planning n=10 interviews with family physicians and n=12 with patients. Sample size considerations for the interviews are based on Guest et al.²⁸

Recruitment of further medical specialists and non-medical service providers will be conducted in parallel as part of the developmental phase based on public information. Providers will be contacted with written study information and a web link to the survey to assess their current practice. We aim to recruit n=250 medical and non-medical providers.

Feasibility phase

The sample size for the feasibility study was planned based on the findings from a subsequent effectiveness study and according to formulas recommended by van Breukelen and Candel²⁹ for randomised cluster studies. The primary outcome will be the EORTC-QLQ-C30 score to measure the quality of life of patients with cancer.³⁰ For the mean differences between follow-up and baseline in the intervention group compared with the control group, a medium effect size with Cohen’s d=0.5 was assumed. This corresponds to approximately half of the estimated effect size of a previous effectiveness study with a comparable research scope.³¹

Assuming a minimum of five patients per practice, an intraclass correlation coefficient of 0.25, a power level of 0.8 and a significance level of 0.05, it was calculated that at least 51 family practices would need to be studied to demonstrate the intervention effect. Assuming a dropout rate of 0.25, the final adjusted sample size is at least 67 general practices. This total number of practices is valid under the assumption that practices are randomly and evenly assigned to a study arm, that ia, approximately 34 practices per study arm. With the baseline assumption of five patients per practice, this would amount to a total of at least 340 patients for the effectiveness study. For the feasibility study planned here, a total of 100 patients from all recruitment sites are targeted with at least 10 family doctors involved. This sample size would enable even limited conclusions regarding feasibility. The sample size calculation was based on a cluster-randomised trial design, assuming a linear mixed effects model with a random intercept for practices and a Gaussian link function. Power was estimated using Monte Carlo simulations (α=0.05, power≥0.80).

The patient collective for the feasibility phase will be drawn from the collective for the developmental phase. For this purpose, all participants from the developmental phase will be invited to take part in the feasibility study. A separate invitation and renewed consent will be issued for this purpose. Participation in the feasibility study is not a prerequisite for participation in the developmental phase.

Furthermore, we will invite family physicians from our research network to participate and test the eLearning system regarding the care of cancer survivors. Participating physicians will receive education credits as well as 100€ to increase willingness to participate. Figure 3 shows the recruitment strategies in a cohesive manner.

Figure 3. Recruitment strategies for the DELPHIN study.

Analyses

The outcomes of the cross-sectional studies, including current care needs and barriers, will first be described using descriptive statistics. Subsequently, group comparisons (eg, χ² tests) and regression analyses will be conducted to examine associations with relevant predictors. In long-term cancer survivors, predictors will include, among others, cancer type and year of first diagnosis. In medical providers, specialty will serve as a central predictor.

For the feasibility study, primary outcomes will initially be analysed descriptively. In a further step, multivariable regression analyses will be applied to identify potential subgroups for whom the DELPHIN intervention is particularly feasible, considering, among others, age, gender and cancer type. Longitudinal data collected within the feasibility study will additionally be analysed using generalised linear models to obtain preliminary evidence regarding effectiveness, as they allow flexible modelling of different outcome types (continuous, binary, count data) and can account for repeated observations per participant over time by including appropriate correlation structures or random effects. The level of statistical significance will be set at 5%. Missing data will be handled listwise if the missing rate is below 5%. Otherwise, imputation procedures will be applied, with the specific method determined by the missing data pattern. We will correct for multiple testing if necessary, performing post-hoc testing.

The content-analytical evaluation of the transcribed semi-structured interviews will be based on Mayring.³² All analyses will be conducted using the current version of IBM's SPSS³³ and MAXQDA.³⁴

Patient and public involvement

In line with the INVOLVE criteria,³⁵ patient representatives are involved at every stage of the DELPHIN project. Two of the patient representatives are part of the project team and were involved in the grant application. They are therefore also part of the author team for this study protocol.

Ethics and dissemination

Ethical considerations and safety

The DELPHIN study will be carried out without any commercial interest of the scientists, clinical staff or study participants involved. We will communicate the study content transparently to participants, the staff involved and the scientific community.

As the primary objective is to inform patients and general practitioners about bio-psycho-social needs and to address these through existing medical and non-medical services within the German healthcare system, no additional risks for patients are anticipated. Patients retain autonomy in decision-making and determine, in consultation with their general practitioners, which healthcare services to use.

All participants will receive written information and will be asked to provide informed consent before enrolment.

Data management and protection

Documented process regulations will be developed throughout the project, which will specify quality criteria for data management and data evaluation, thus regulating quality assurance. Quality control will be done on a regular basis throughout the project. Only trained and selected project staff have access to personal data used in the recruitment process as well as the final study data set. Both databases are stored separately. Data will be pseudonymised for analyses. All data are stored on secured servers.

Public dissemination, transfer and implementation

Positive and negative study results will be published in full, preferably in open-access journals with international standards in accordance with the reporting guidelines of the EQUATOR network. All relevant protocol changes will be submitted to the Ethics Committee of the Medical Faculty at the University of Bonn. Where possible, the FAIR data principles will be applied in consultation with the data protection officer of the University Hospital Bonn.

Trial status and dates

The study started in April 2024 and will be continued until March 2028. As of 2026, we are currently conducting study 1, the developmental study. All three study parts are conducted in parallel by the project partners.

Discussion

To date, no patient-centred and family physician-led care system exists in Germany to support long-term cancer survivors, although a substantial proportion of this population experiences bio-psycho-social long-term and late effects.^{12 18} At the same time, family physicians are considered key actors in the provision of comprehensive cancer care.²⁰ After 5 years, most cancer survivors in Germany formally exit medical follow-up care, often leaving them without access to structured support systems. For this group in particular, innovative and sustainable care models, like DELPHIN, are highly relevant.

The DELPHIN study aims to develop a digital screening tool for long-term cancer survivors that systematically identifies and addresses their current bio-psycho-social needs. Family physicians act as trusted confidants with whom consultations can take place and further care decisions can be made. By building on existing structures, the DELPHIN intervention avoids the need to establish parallel systems. Furthermore, we will be able to target the heterogeneous group of long-term cancer survivors with their different diagnoses, past treatments and further factors.¹⁶ From a health system perspective, leveraging primary care as a hub for survivorship support may increase efficiency and cost-effectiveness compared with creating new, specialised infrastructures. In the long run, this is expected to improve access to health and social services for long-term cancer survivors.

The DELPHIN intervention aims to cover secondary and tertiary prevention among long-term cancer survivors, and to our knowledge, this is the first attempt to establish a comprehensive, digital care system for this group in Germany. The development process will be guided by triangulated qualitative and quantitative evidence from both our own data and the international literature, as recommended.²²

A major limitation of the study concerns the recruitment process of participants. Long-term cancer survivors will be approached, via family physicians, the Center of Integrated Oncology of the University Hospital Bonn, local self-help groups and through public advertisements, which may introduce selection bias. In addition, individuals with limited technological literacy could hesitate to access or participate in the study. To mitigate these limitations, post-stratification weighting based on representative population data will be applied.³⁶

Following feasibility testing, we will seek to demonstrate the effectiveness of the intervention, particularly regarding health-related quality of life among cancer survivors. In the long term, the DELPHIN intervention is expected to support survivors in navigating the complex German health and social care system while simultaneously generating further insights into their specific needs. By integrating a digital, family physician-led approach into routine care, the intervention also holds potential to improve equity: individuals with limited access to specialist services, lower health literacy or greater socioeconomic disadvantage may particularly benefit from a system embedded in primary care.