Germline Genetic Mutations in a Multi-Center Cohort of 248 Phyllodes Tumors

Abstract

PURPOSE:

Germline genetic mutations in women with phyllodes tumors (PT) are understudied, although some describe associations of PT with various mutations. We sought to determine the prevalence of pathogenic/likely pathogenic (P/LP) variants in women with PT.

METHODS:

A 6-site multi-center study of women with a PT was initiated, then expanded nationally through an online “Phyllodes Support Group”. All women underwent 84-gene panel testing. We defined eligibility for testing based on select NCCN (National Comprehensive Cancer Network) criteria (v1.2022). Logistic regression was used to estimate the association of covariates with the likelihood of a P/LP variant.

RESULTS:

274 women were enrolled; 164 (59.9%) through multi-center recruitment and 110 (40.1%) via online recruitment. 248 women completed testing; overall 14.1% (N=35) had a P/LP variant, and over half (N=19) of these individuals had a mutation in genes associated with autosomal dominant (AD) cancer conditions. The most common AD genes with a P/LP variant included CHEK2, ATM, and RAD51D. A quarter of participants (23.8%) met NCCN criteria for testing, but we found no difference in prevalence of a P/LP variant based on eligibility (p=0.54). After adjustment, presence of P/LP variants was not associated with age, NCCN testing eligibility, or PT type (all p>0.05).

CONCLUSION:

Our study demonstrates that 7.7% of women with PT harbor germline P/LP variants in genes associated with AD cancer conditions. Early identification of these variants has implications for screening, risk-reduction, and/or treatment. National guidelines for women with PT do not currently address germline genetic testing, which could be considered.

BACKGROUND

Phyllodes tumors (PT) are rare primary breast neoplasms representing 0.3 – 1.0% of all breast tumors, ^1,2 and are identified in women with a median age of 40–45. ³ Although commonly diagnosed at a young age, which can signal a potential genetic etiology, there remains sparse data regarding germline genetic susceptibility for PT. A few germline pathogenic/likely pathogenic (P/LP) variants have been described in case reports and small series^{4, 5}. These studies have reported P/LP variants in BRCA1, RB1, and TP53 genes. ^6–12 The most compelling data in the literature suggesting potential heritability comes from a study of 28 families with Li-Fraumeni syndrome (TP53),⁹ which found the greatest increase in specific cancers relative to the general population were in adrenocortical carcinoma and malignant PT. ⁹ However, the prevalence and types of P/LP variants in women with a PT are currently unknown.

We previously conducted a multi-center retrospective data collaborative of women with PT (N=550), revealing 20.4% (N=112) had ≥3 family members with cancer, suggestive of a hereditary cancer syndrome. ¹³ Notably, only a small fraction of the cohort underwent germline testing (6.2%, N=34), and many of those had only BRCA1/BRCA2 testing, excluding genes potentially associated with PT. Of the 34 patients tested, 8.8% (N=3) had a germline P/LP variant identified (1 in BRCA1, and 2 in TP53), a similar rate to that seen in cohorts of women with breast adenocarcinoma. ¹⁴

Currently, the National Comprehensive Cancer Network (NCCN) practice guidelines for PT do not specifically recommend consideration of germline genetic testing for hereditary cancer syndromes. ¹⁵ Even within the Li-Fraumeni (TP53) Syndrome Testing Criteria, PT are not specifically listed with the other syndrome-associated Li-Fraumeni tumors (e.g. osteosarcoma, soft tissue sarcoma, central nervous system tumor, breast cancer, adrenocortical carcinoma). However, the findings from our retrospective data collaborative suggested a potential signal between PT and select germline P/LP variants, ¹³ and if validated, confirmation of this association could have a significant impact for these women with PT and their families. Therefore, we performed multi-gene germline genetic testing in a cohort of women with a history of a PT to determine: 1) the overall prevalence and types of germline mutations in women with PT, and 2) the difference in germline mutation rates between histologic subtypes of PT (benign, borderline, or malignant).

PATIENTS and METHODS

Study Recruitment

We performed a multi-center, cohort study including six comprehensive cancer centers and subsequent inclusion of a “Phyllodes Support Group” via a social media platform (Facebook^®). Following Institutional Review Board approval at each site, women included in the previously reported PT multi-center data collaborative (N=550)¹³ were contacted by the treating institution for individual consent, enrollment, and testing (initiated 3/2020). With slow accrual during the COVID-19 pandemic, recruitment was expanded six months thereafter to permit inclusion of any woman with a PT treated at each of the six initial sites. Subsequently, recruitment was again expanded six months later to permit recruitment nationally through the Facebook^® platform via self-identification in the “Phyllodes Support Group”. The women recruited through the online platform had their final surgical pathology verified electronically and were enrolled, consented, and tested through the study coordinating center. Women recruited through the “Phyllodes Support Group” had completely virtual enrollment and participation.

Germline Genetic Testing

After consent, women at each site completed the Multi-Cancer Panel (84-genes) test (Table 1) by Invitae^® (Invitae Corporation, San Francisco, CA), at no cost to the participant supported by a research grant at the coordinating center. Genetic test results were reported to the participant by each participating site. During the consent encounter (virtual or in-person) family history was updated for those established through the academic centers, and obtained for those recruited through the online platform. Questions targeted a multi-generational family history for all cancers and specifically asked about family history of breast, ovarian, uterine, gastric, colorectal, pancreatic, renal, thyroid, or any other tumors. We identified women that met the criteria for further genetic risk evaluation based on the v1.2022 NCCN “Genetic/Familial High-Risk Assessment: Breast, Ovarian, and Pancreatic” guidelines. ¹⁵ (Suppl. Methods) As we did not have age of diagnosis abstracted for the family cancer history, or specifically if prostate cancer was metastatic, we could not include the following criteria from the NCCN guidelines; 1^st- or 2^nd-degree relative with the following (1) breast cancer at age ≤45 years, (2) ≥2 individuals with breast cancer primaries on the same side of the family with at least one diagnosed at ≤50 years, or (3) metastatic prostate cancer.

Table 1.

Hereditary Cancer Genes included in the Multi-Cancer Panel at the time of this study (84-genes), including those associated with Hereditary Breast, Gynecologic, Gastrointestinal, Genitourinary, Endocrine, Brain and Spinal cord, Soft Tissue Sarcoma, and Hematologic Malignancies.

AIP	ALK	APC	ATM	AXIN2	BAP1	BARD1
BLM	BMPR1A	BRCA1	BRCA2	BRIP1	CASR	CDC73
CDH1	CDK4	CDKN1B	CDKN1C	CDKN2A	CEBPA	CHEK2
CTNNA1	DICER1	DIS3L2	EGFR	EPCAM	FH	FLCN
GATA2	GPC3	GREM1	HOXB13	HRAS	KIT	MAX
MEN1	MET	MITF	MLH1	MSH2	MSH3	MSH6
MUTYH	NBN	NF1	NF2	NTHL1	PALB2	PDGFRA
PHOX2B	PMS2	POLD1	POLE	POT1	PRKAR1A	PTCH1
PTEN	RAD50	RAD51C	RAD51D	RB1	RECQL4	RET
RUNX1	SDHA	SDHAF2	SDHB	SDHC	SDHD	SMAD4
SMARCA4	SMARCB1	SMARCE1	STK11	SUFU	TERC	TERT
TMEM127	TP53	TSC1	TSC2	VHL	WRN	WT1

APPENDIX

Supplemental Methods:

Utilizing the NCCN criteria (v1.2022 “Genetic/Familial High-Risk Assessment: Breast, Ovarian, and Pancreatic” guidelines), women with a personal history of PT alone are typically considered an unaffected individual, as the NCCN guidelines define those to be included as: “for the purposes of these guidelines, invasive and ductal carcinoma in situ breast cancers should be included” (CRIT-2A, footnote “h”) ¹⁵. Similarly, the NCCN testing criteria for Li-Fraumeni (TP53) Syndrome do not include PT as one of the syndrome-associated Li-Fraumeni tumors (e.g. osteosarcoma, soft tissue sarcoma, central nervous system tumor, breast cancer, adrenocortical carcinoma). Therefore, women with PT are often deemed ineligible for testing by genetic counselors and/or insurance carriers.

For an unaffected individual, women would only meet criteria for further genetic risk evaluation based on separate existing criteria for genetic testing including other personal history of other cancers or by family history. These included individuals who had a 1^st or 2^nd-degree relative with ovarian or pancreatic cancer, or male breast cancer. Additionally, these criteria included women with a 1^st-, 2^nd-, or 3^rd-degree family history of three or more of the following on the same side of the family (including multiple primary cancers in the same individual): brain, breast, colorectal, kidney/renal or bladder, leukemia, lymphoma, ovarian, pancreatic, prostate, sarcoma, stomach, thyroid, and uterine (endometrial).

Statistical Analyses

Demographics were summarized with N (%) for categorical variables and median (interquartile range, IQR) for continuous variables. Genetic test results were summarized with N (%) by recruitment site and by PT subtype (benign, borderline, or malignant). Differences were tested using the chi-square or Fisher’s exact test for categorical variables and the t-test for continuous variables. A logistic regression model was used to estimate the association of age, PT grade, and select NCCN eligibility with the odds of having a germline P/LP mutation. This model was built in the generalized estimating equations framework with an exchangeable correlation structure to account for women from the same site. No adjustments were made for multiple comparisons, and a p-value ≤0.05 was considered statistically significant. All statistical analyses were conducted using SAS, version 9.4 (SAS Institute, Cary NC).

RESULTS

This multi-center prospective study enrolled 274 women with PT, 59.9% (N=164) who were enrolled from six academic institutions, and 40.1% (N=110) who were self-identified via the online social media platform (Facebook^®). Table 2 Of the 274 women enrolled, 248 completed the germline genetic testing. The percentage of women who completed testing was relatively evenly distributed across all sites. Of the N=26 that did not complete testing, the most common reasons cited for not proceeding to testing was (1) not interested in a research-only appointment for genetic testing during the COVID-19 pandemic and (2) ongoing concerns regarding future life insurance eligibility if a pathogenic mutation would be identified. All participants were female, had a median age of 44 years (range, 12 – 76), and were predominantly White (70.6%, Black 5.8%, Asian 4.1%, Other 2.9%, Unknown 17.4%), and non-Hispanic/Latino (77.8%, Hispanic/Latino 5.0%, Unknown 17.4%). All subtypes of PT were eligible for participation and approximately equal distribution of each histologic type of PT was observed (benign: 36.7%, N=91; borderline: 27.8%, N=69; and malignant: 33.9%, N=84), which is an overrepresentation of the higher grade phyllodes. Four individuals with a missing subtype (1.6%).

Table 2.

Germline Genetic Testing and Results for Women with Phyllodes Tumors by Enrollment Location.

	Total Cases	“Phyllodes Support Group”	Site 1	Site 2	Site 3	Site 4	Site 5	Site 6
Age at diagnosis, years * (IQR)	44 (37 – 53)	43 (34 – 53)	46 (40 – 54)	-	46 (40 – 53)	40 (24 – 55)	41 (38 – 52)	51 (46 – 58)
Consented, enrolled	274	110	62	36	32	13	13	8
Testing completed	248	105	56	32	27	11	9	8
P/LP variant identified	36	14 B = 3 BL = 4 M = 7	9 B = 4 BL = 1 M = 3 Unk = 1	4 B = 1 BL = 0 M = 3	6 B = 3 BL = 2 M = 1	0	1 B = 0 BL = 1 M = 0	2 B = 0 BL = 2 M = 0
P/LP variant rate	14.1%	13.3%	16.1%	12.5%	22.2%	0%	11.1%	25%
VUS only	103	44	23	11	11	7	3	4
P/LP gene variants		APC	BLM	CHEK2	ATM	-	BARD1	CHEK2
		BLM	CHEK2	MSH6	ATM			MUTYH
		BLM	HOXB13	MUTYH	MITF
		BLM	HOXB13	RECQL4	MUTYH
		CHEK2	MUTYH		RAD51D
		MITF	MUTYH		SDHA
		MUTYH	NTHL1
		MUTYH	POT1
		POLE	TP53
		RAD51C
		RAD51D
		RECQL4
		WRN
		WRN

^*For Facebook^™ “Phyllodes Support Group”, age is at study enrollment

B: Benign phyllodes tumor; BL: Borderline phyllodes tumor; IQR: Interquartile Range; M: Malignant phyllodes tumor; P/LP: Pathogenic/Likely Pathogenic; VUS: Variant of Uncertain Significance

Of the 248 women with available results, 14.1% (N=35) had a P/LP variant (Table 2). Of these 35 patients, 19 individuals (54.3%) were found to have P/LP variants (20 mutations total) in genes associated with autosomal dominant (AD) cancer conditions (7.7% of the overall cohort), while 16 women (45.7%) were found to be heterozygous for a P/LP variant in genes associated with autosomal recessive (AR) conditions (6.5% of the overall cohort). The most common genes associated with an AD variant in order of frequency (highest to lowest) of identification included; CHEK2 (N=4), APC (N=2), ATM (N=2), HOXB13 (N=2), MITF (N=2), RAD51D (N=2), BARD1 (N=1), MSH6 (N=1), POT1 (N=1), RAD51C (N=1), SDHA (N=1), TP53 (N=1), while those with an AR P/LP variant were; MUTYH (N=7), BLM (N=4), WRN (N=2), NTHL1 (N=1), POLE (N=1), RECQL4 (N=1) (Table 3).

Table 3.

Germline Genetic Testing Results including Genes, P/LP Variant, Interpretation, and Phyllodes Type

	Gene†	Effect	Interpretation	Result	Phyllodes
Genes associated with autosomal dominant conditions in heterozygous state
1	APC	p.Ile1307Lys	Increased Risk Allele	Increased Risk	Malignant
2	HOXB13	p.Gly84Glu	Increased Risk Allele	Increased Risk	Benign
3	HOXB13	p.Gly84Glu	Increased Risk Allele	Increased Risk	Benign
4	ATM	p.Phe2799Lysfs*4	Pathogenic	Positive	Borderline
5	ATM	p.Glu2039Val	Likely Pathogenic	Positive	Benign
6	APC; CHEK2	p.Ile1307Lys; p.Thr367Metfs*15	Increased Risk Allele; Pathogenic	Positive	Borderline
7	BARD1	p.Tyr180*	Pathogenic	Positive	Borderline
8	CHEK2	p.Ile157Thr	Pathogenic‡	Positive	Malignant
9	CHEK2	Intronic	Likely Pathogenic	Positive	Malignant
10	CHEK2	p.Arg117Gly	Pathogenic	Positive	Malignant
11	MITF	p.Glu318Lys	Pathogenic	Positive	Borderline
12	MITF	p.Glu318Lys	Pathogenic	Positive	Benign
13	MSH6	p.Arg1068*	Pathogenic	Positive	Malignant
14	POT1	Splice acceptor	Pathogenic	Positive	Benign
15	RAD51C	p.Cys135Tyr	Pathogenic	Positive	Borderline
16	RAD51D	p.Ser207Leu	Pathogenic	Positive	Malignant
17	RAD51D	Splice donor	Likely Pathogenic	Positive	Malignant
18	SDHA	p.Arg31*	Pathogenic	Positive	Benign
19	TP53	p.His214Glnfs*7	Pathogenic	Positive	Malignant
Genes associated with autosomal recessive conditions in heterozygous state
1	BLM	p.Arg899*	Pathogenic	Carrier	Benign
2	BLM	p.Thr494Profs*9	Pathogenic	Carrier	Benign
3	BLM	p.Gln548*	Pathogenic	Carrier	Malignant
4	BLM	p.Leu751Lysfs*25	Pathogenic	Carrier	Borderline
5	MUTYH	p.Arg274Gln	Pathogenic	Carrier	Benign
6	MUTYH	p.Gly396Asp	Pathogenic	Carrier	Benign
7	MUTYH	p.Gly396Asp	Pathogenic	Carrier	Borderline
8	MUTYH	p.Gly396Asp	Pathogenic	Carrier	Malignant
9	MUTYH	p.Gly396Asp	Pathogenic	Carrier	Borderline
10	MUTYH	p.Tyr179Cys	Pathogenic	Carrier	Borderline
11	MUTYH	p.Tyr179Cys	Pathogenic	Carrier	Borderline
12	NTHL1	p.Gln90*	Pathogenic	Carrier	Benign
13	POLE	p.Arg1909*	Pathogenic	Carrier	Borderline
14	RECQL4	p.Trp379*	Pathogenic	Carrier	Malignant
15	WRN	p.Gly744Glufs*20	Pathogenic	Carrier	Malignant
16	WRN	p.Arg369*	Pathogenic	Carrier	Malignant

^†Zygosity for all gene results were heterozygous

^‡Low penetrance

P/LP: Pathogenic/Likely Pathogenic

The frequency of an individual having a variants of uncertain significance (VUS), in the absence of a P/LP variant finding, was 41.5% (N=103). VUS results were identified in 61 individual genes, with no instances of duplicate or identical VUS’s. The genes with the most frequent VUSs, in order of frequency of identification, were POLE (N=11), APC (N=8), ATM (N=7), and WRN (N=7).

Pathogenic/likely pathogenic variants were detected across the complete spectrum of participants’ ages; the youngest two were 12 years old at diagnosis (1 SDHA and 1 MUTYH, both heterozygous), and the oldest was age 70 (1 NTHL1 and 1 BARD1, both heterozygous). Notably, a TP53 P/LP variant was identified in a 24-year-old (who did not meet Li-Fraumeni syndrome testing criteria).

Numerically, a P/LP variant was more frequent in higher grade PT (benign 12.1%, borderline 14.5%, malignant 16.7%); however, these differences were not statistically significant (p=0.69). For genes specifically associated with AD conditions, a P/LP variant was also detected in higher frequency with malignant PT (benign 6.6%, borderline 5.8%, malignant 9.5%, p=0.64; Table 4).

Table 4.

Genetic Testing Results, Pathogenic/Likely Pathogenic Variants, by Phyllodes Tumor Grade^*.

	Benign (N=91)	Borderline (N=69)	Malignant (N=84)
P/LP variant, N (%)	11 (12.1%)	10 (14.5%)	14 (16.7%)
P/LP variant, autosomal dominant, N (%)	6 (6.6%)	4 (5.8%)	8 (9.5%)
VUS only, N (%)	32 (35.2%)	32 (46.4%)	37 (44.0%)

^*Excludes four women with unknown phyllodes grade

P/LP: Pathogenic/Likely Pathogenic; VUS: Variant of Uncertain Significance

Chi-square test for any difference: (12.1% vs. 14.5% vs. 16.7%, p=0.69)

Pairwise testing for difference between tumor grades:

Benign vs. borderline (12.1% vs. 14.5%, p=0.66)

Benign vs. malignant (12.1% vs. 16.7%, p=0.39)

Borderline vs. malignant (14.55 vs. 16.7%, p=0.71)

Based on family history, 23.8% of women (N=59) in the overall cohort met NCCN criteria (v1.2022) for germline genetic testing. There was no significant difference in the P/LP variant rate for those eligible for genetic testing based on NCCN guidelines, as compared to those who were ineligible (17.0% [N=10/59] vs. 13.8% [N=26/189], p=0.54). On multivariable analysis, presence of a P/LP variant was not associated with age at diagnosis (OR=1.00, p=0.95), NCCN genetic testing eligibility (OR=1.06, p=0.93), or PT type (malignant vs. benign, OR=1.07, p=0.72; Table 5).

Table 5.

Adjusted Logistic Regression Model for Identification of a Pathogenic/Likely Pathogenic Mutation. (N=212)

Covariate	Odds Ratio (95% CI)	p-value	Overall p-value
Age at Diagnosis (Years)	1.00 (0.97 – 1.03)	0.95	0.95
Grade			0.94
- Benign (grade 1)	Reference
- Borderline (grade 2)	0.99 (0.51 – 1.91)	0.97
- Malignant (grade 3)	1.07 (0.73 – 1.58)	0.72
NCCN Genetic Testing Eligibility			0.93
- Ineligible	Reference
- Eligible	1.06 (0.29 – 3.91)	0.93

CI: Confidence Interval; NCCN: National Comprehensive Cancer Network

DISCUSSION

In this prospective cohort study of 248 women with PT, 14.1% were found to have at least one P/LP variant. Among the variants, 54.3% had mutations in known autosomal dominant hereditary cancer susceptibility genes. This is equivalent to an overall AD mutation prevalence of 7.7%, which is similar to the mutation rate observed in unselected breast cancer populations. ^{14, 16} To our knowledge, this is the first study to evaluate a cohort of women with PT for a germline P/LP variant. Our findings reveal that patients with PTs may have an overall higher mutation rate than would be expected in the general (non-breast cancer) population.

In comparison to our findings, a large cohort study of nearly 30,000 participants from the Healthy Nevada Project found a 1.33% combined carrier rate for P/LP variants for hereditary breast and ovarian cancer, Lynch Syndrome, and Familial Hypercholesterolemia. ¹⁷ While this study included a focused set of genes, it reveals a very low population carrier rate of the genes most often responsible for hereditary cancer syndromes (e.g. BRCA1, BRCA2). Notably, 90% of carriers in this study had not been previously identified. ¹⁷ Similarly, a study of nearly 6,000 healthy Australian women demonstrated a 0.64% carrier rate of a high-risk clinically actionable pathogenic variant. ¹⁸ Similar to our own findings, this Australian study demonstrated low population carrier rates in genes with P/LP variants; ATM (N=18 pathogenic variant, 0.30% population frequency), TP53 (N=0), RAD51C (N=2, 0.04%), and RAD51D (N=2, 0.04%). Taken together, these population-based studies suggest an approximately 1% carrier rate in the average population for a known mutation in a hereditary cancer gene. However, it is important to note that some of these studies were based on older cohorts of unaffected patients, which would presumably lower the odds of identifying pathogenic variants. Nonetheless, we have demonstrated that women with PTs may have an increased risk of harboring a germline predisposition to cancer.

Previous reports have suggested the possibility of a genetic susceptibility for these rare breast tumors, including case reports describing a mother and daughter both with benign PT⁴, and two sisters (one borderline and one malignant PT)⁵. Neither case report indicates that any germline genetic testing had been performed. Although we were unable to include all of the criteria, fewer than 25% of women in our study met the Breast, Ovarian, and Pancreatic NCCN criteria (v1.2022) for testing. Interestingly, however, detection of a P/LP variant was similar regardless of NCCN eligibility for testing. With no known environmental risk factors, these prior reports and our own findings suggest that some PT may arise due to cancer predisposing germline mutations.

Specific germline mutations in patients with PT have been previously reported, including (1) a pathogenic BRCA1 germline mutation (missense C5214T, R1699W),⁶ (2) multiple cases of malignant phyllodes in patients with hereditary retinoblastoma (RB1 gene)^{7, 8}, and (3) numerous cases associated with TP53 mutations.^9–12 The strongest data in the literature to support a genetic predisposition for the development of phyllodes was reported in a study evaluating 28 families with Li-Fraumeni syndrome and a germline TP53 mutation.⁹ The authors found the greatest increases in cancers relative to the general population rates were in adrenocortical carcinoma and malignant PT.⁹ Several studies have confirmed various germline mutations in TP53 in women with PT, including some of our previous work.^8–10 We identified one patient in our current cohort with a TP53 mutation and two patients in our original retrospective multi-institutional study

However, the most common genes with pathogenic mutations in our current cohort included MUTYH, BLM, CHEK2, and ATM. We acknowledge that no BRCA1 or BRCA2 mutations were identified, although this was not particularly surprising, as the current NCCN guidelines and risk assessment tools ¹⁹ were developed with the primary goal of identifying BRCA1 and BRCA2 mutation carriers. Thus, any patient with a PT that met those criteria may have previously undergone testing as a part of their routine clinical care. In our previous work, only 6.2% (N=34) of the 550 patients with PT had undergone genetic testing, and of those who underwent genetic testing, 38.2% (N=13/34) had only BRCA1/2 testing. Nevertheless, that study demonstrated that among women who underwent germline genetic testing as a part of their routine clinical care, 8.8% were found to have a P/LP variant, including one patient with a BRCA1 mutation. ¹³ In the current study, we further demonstrated that the presence of a P/LP variant was not associated with age at diagnosis, NCCN testing eligibility, or PT subtype, suggesting that current genetic testing guidelines do not adequately identify patients with PT who may harbor a pathogenic germline mutation.

Most would agree that identifying germline genetic mutations has clinical implications. Multiple germline P/LP variants identified in this cohort convey a significant lifetime breast cancer risk including TP53, ATM, BARD1, and CHEK2. Together, these P/LP variants were identified in nearly a quarter of our population of women found to have mutations, with each gene conveying a >20% lifetime risk of breast cancer and thus meeting national criteria for high-risk breast cancer screening. For those with a TP53 mutation, whole body MRI (including breast) screening is recommended at diagnosis. In the largest Li-Fraumeni Syndrome series, including 214 families and 322 individual TP53 carriers, the mean age of diagnosis with the first tumor was 25 years, with 41% having developed at least one tumor by age 18, and 79% of women diagnosed with a breast carcinoma. ²⁰ Additionally, multiple of the P/LP variants in our cohort were identified in genes associated with a colorectal cancer risk including; APC, CHEK2, MSH6, MUTYH (when homozygous), and TP53. While the APC P/LP variant identified in this cohort is not associated with familial polyposis syndrome, it leads to a 5–10% lifetime risk for non-polyposis colon cancer, with screening coloscopy recommended to start at age 40 and repeat every 5 years. Identification of these germline mutations offers additional screening opportunities and/or risk-reducing strategies in various cancer types when appropriate based on specific variant and family history. Lastly, P/LP variants in RAD51C and RAD51D, convey a 5–10% lifetime risk of ovarian cancer, which is markedly higher than a non-carrier (1%), and national guidelines recommend consideration of a risk-reducing salpingo-oophorectomy at the age of 45. This is particularly important as the median age of a PT diagnosis is in a woman’s early 40s, permitting early screening, intervention, and/or cascade testing.

Notably, phyllodes tumors may be the presenting event in these young women and may represent a de novo mutation, which would not be predicted based on one’s family history. Regardless, identifying a germline mutation would (1) impact future screening strategies, (2) provide the ability to offer risk-reducing strategies, and (3) may have significant implications for their families. Lastly, a few of these mutations, such as TP53, may have critical treatment implications; for example, we would not offer radiation therapy to a woman with a TP53 mutation due to the significant increased risk of radiation-associated secondary malignancies. Taken together, our findings highlight a critical need for additional investigation to help further clarify the potential association between phyllodes tumors and germline genetic mutations.

While our findings represent the largest known prospective study to date on germline genetic testing in women with PT, there were some limitations. Our initial approach was to offer testing to women who were previously identified as having a PT in our multi-institutional retrospective cohort. However, recruitment was lower than anticipated, and therefore, we elected to open the study to newly identified patients with PT at those same institutions and to those self-referred through an online community. These varying methods of recruitment may have introduced potential bias into our study, which cannot be fully accounted for. The similar age and frequency of P/LP variants between the two cohorts is reassuring. The result of this limitation could be a possible oversampling of a cohort with stronger family histories of cancer, or a cohort that was previously not offered genetic testing during routine clinical care. In addition, family history questions did not specifically include age of cancer diagnosis of family members, history of Ashkenazi Jewish ancestry, or personal history of other cancer. Another limitation is the missing data for select patients and variables. While most patients had complete data sets, it is possible that the missing data was not random, and this could have also introduced unintended bias into our study findings. Similarly, the family history data was not as granular as needed to assess complete NCCN testing eligibility.

CONCLUSION

In this large cohort of women with PT who underwent germline genetic testing, we found that 7.7% harbored P/LP variants that are associated with autosomal dominant hereditary cancer risk, for which high-risk screening guidelines or risk-reducing strategies exist. Therefore, our study highlights an area in need of further exploration, and if the findings remain consistent, national guidelines may need to consider further defining the potential need for germline genetic testing for women with PT.