BRCA1, TP53, and CHEK2 Germline Mutations in Uterine Serous Carcinoma

Abstract

Background

Uterine serous carcinoma (USC) is not recognized as part of any defined hereditary cancer syndrome, and its association with hereditary breast and ovarian carcinoma and Lynch syndrome are uncertain.

Methods

Using targeted capture and massively parallel genomic sequencing, we assessed 151 subjects with USC for germline mutations in 30 tumor suppressor genes, including BRCA1, BRCA2, the DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2), TP53, and ten other genes in the Fanconi anemia (FA)-BRCA pathway. Ten cases with <10% serous histology were also assessed.

Results

Seven subjects (4.6%) carried germline loss-of-function mutations: three (2.0%) in BRCA1, two (1.3%) in TP53, and two (1.3%) in CHEK2. One subject with <10% serous histology had an MSH6 mutation. Subjects with MSH6 and TP53 mutations had neither personal nor family histories suggestive of Lynch or Li-Fraumeni syndromes. Of the 22 women with USC and a personal history of breast carcinoma, the frequency of BRCA1 mutations was 9%, compared to 0.9% in 119 women with no such history.

Conclusions

Approximately 5% of women with USC have germline mutations in three different tumor suppressor genes: BRCA1, CHEK2, and TP53. Mutations in DNA mismatch repair genes that cause Lynch syndrome are rare in USC. The germline BRCA1 mutation rate in USC subjects of 2% is higher than expected in a non-founder population, suggesting that USC is associated with hereditary breast and ovarian carcinoma in a small proportion of cases. Women with USC and breast cancer should be offered genetic testing for BRCA1 and BRCA2 mutations.

INTRODUCTION

Targeted capture and massively parallel sequencing allows for highly reliable mutation analysis of multiple genes of interest simultaneously. We have applied this technique to develop a test we refer to as BROCA, which sequences thirty tumor suppressor genes, including BRCA1, BRCA2, the DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2), TP53, and ten genes in the Fanconi anemia (FA)-BRCA pathway. Using BROCA, we evaluated germline DNA from 360 women with ovarian, fallopian tube, and peritoneal carcinoma: 23% of subjects had germline loss-of-function mutations. Mutations were identified in 12 genes, including every gene in the FA-BRCA pathway tested except ATM, suggesting that this pathway is widely implicated in hereditary ovarian carcinoma ¹. The potential involvement of the FA-BRCA pathway has not been comprehensively assessed in endometrial carcinoma.

While ovarian carcinoma has the highest mortality rate, endometrial carcinoma is the most common gynecologic malignancy in the United States. Although uterine serous carcinoma (USC) represents only 10% of all endometrial cancers, it accounts for up to 40% of endometrial cancer-related deaths ². In contrast to the more common endometrioid histology, USC is more likely to present in advanced stage and carries a worse prognosis. USC mimics the most common histology of ovarian carcinoma and has a similar proclivity for intra-peritoneal spread and high frequency of somatic TP53 mutations. Like ovarian carcinomas, endometrial carcinomas can be of mixed histologies, and even minor fractions of serous histology seem to confer a more aggressive phenotype in endometrial carcinomas ³.

Currently, USC is not recognized as a feature of any hereditary cancer syndrome, but many have speculated a possible association with hereditary breast and ovarian cancer ^4–8. Geisler et al. found a higher incidence of subsequent breast carcinoma in women with USC compared to endometrioid endometrial carcinoma ⁹. Studies investigating the association between USC and germline BRCA1 and BRCA2 (BRCA1/2) mutations have revealed conflicting results, included small numbers of subjects, and did not differentiate between USC with purely serous features and those with mixed histologies ^5–8. Therefore, it is not certain whether USC is part of the cancer spectrum for BRCA1 and BRCA2 mutation carriers.

It is also uncertain whether USC is associated with Lynch syndrome caused by germline mutations in DNA mismatch repair genes (MSH2, MLH1, MSH6, PMS2), in which endometrial carcinoma is a major manifestation. While the majority of Lynch-associated endometrial carcinoma has endometrioid histology, USC has been described for a small number of Lynch patients ¹⁰. Studies of unselected endometrial carcinoma subjects estimate a germline mutation rate in the DNA mismatch repair genes of approximately 2%, but only included very small numbers of USC cases ^11–13. Therefore, the frequency of Lynch syndrome amongst unselected USC is not known.

A better understanding of inherited mutations associated with USC might allow targeted prevention in at risk women. We therefore sought to characterize loss-of-function germline mutations in 30 tumor suppressor genes using BROCA in a large prospectively acquired cohort of USC.

METHODS

Study Subjects

Individuals eligible for study were those with endometrial carcinoma designated as serous histology (either purely serous or mixed) who underwent surgery at Washington University St. Louis or at the University of Washington and provided informed consent to participate in the respective institutional gynecologic oncology tissue banks as approved by human subjects divisions of the institutional review boards. All subjects with USC that had lymphocytes collected at or before surgery were included, regardless of age, family history, or other clinical features suggestive of genetic predisposition to cancer. Cases of mixed histology were included, defined by having at least 10 percent serous histology. Additional cases with any fraction of serous histology <10% were also analyzed, but not included in the final mutation rate, since they did not formally meet criteria for mixed USC. We elected to assess these cases because at least one study suggests that the presence of low fractions of serous component (<10%) worsens prognosis, implying a different biology than purely endometrioid histologies ³. All pathology specimens were reviewed by a gynecologic pathologist to confirm the diagnosis of USC. Information about ethnic backgrounds, clinical information, and personal/family histories were retrieved from medical records. Genomic DNA was extracted from lymphocytes in peripheral blood samples.

Library Construction, Hybridization, and Massively Parallel Sequencing

Three micrograms of germline DNA from each subject was sonicated to a peak of 200bp on a Covaris E series instrument (Covaris, Woburn, MA). Paired end libraries were prepared in 96 well plate format using the SureSelectXT enrichment system on a Bravo liquid-handling instrument (Agilent, Santa Clara CA). Individual paired end libraries (500ng) were hybridized to a 1.1Mb custom design of cRNA biotinylated oligonucleotides targeting 30 genomic regions (Table 1). Following capture, each library was PCR amplified with primers containing a unique 6bp index and quantified by High Sensitivity chip (Agilent, Santa Clara CA). Equimolar concentrations of 96 libraries were pooled to a final concentration of 11pM, cluster amplified on a single lane of v3 flowcell and sequenced with 2×101bp paired end reads and a 7bp index read using SBS v3 chemistry on a HiSeq2000 (Illumina, SanDiego, CA). Sample median depth of coverage was 302x and the percent of targeted bases at >10x and >50x depth was 99.4% and 95.7%, respectively.

Table 1.

Genomic regions targeted for capture

Gene	Regions targeted for capture* (UCSC hg19)
APC	chr5:112038202-112186936
ATM	chr11:108088559-108244826
BAP1	chr3:52430027-52449009
BARD1	chr2:215588275-215679428
BMPR1A	chr10:88511396-88689944
BRCA1	chr17:41191313-41282500
BRCA2	chr13:32884617-32978809
BRIP1	chr17:59754985-59945755
BUB1B	chr15:40448210-40518335
CDH1	chr16:68766195-68874444
CDK4	chr12:58137005-58151164
CDKN2A	chr9:21962751-21999490
CHEK2	chr22:29078731-29142822
KIT	chr4:55519095-55611879
MLH1	chr3:37029979-37097337
MRE11A	chr11:94145467-94232040
MSH2 (+EPCAM)	chr2:47595263-47715360
MSH6	chr2:48005221-48039092
MUTYH	chr1:45789914-45811142
NBN	chr8:90940565-91001899
PALB2	chr16:23609483-23657678
PMS2	chr7:6007870-6053737
PTEN (+KILLIN)	chr10:89618195-89733532
RAD50	chr5:131887630-131984595
RAD51C	chr17:56764963-56816692
RET	chr10:43567517-43630795
SMAD4	chr18:48550583-48616409
STK11	chr19:1200798-1233434
TP53	chr17:7566720-7595863
VHL	chr3:10178319-10198744

^*Repetitive regions removed by RepeatMasker

Mutation Analysis

The BROCA panel accurately identifies all classes of mutations, including single-base substitutions, small insertions and deletions, and large gene rearrangements ¹⁴. Sequence alignment and variant calling were performed against the reference human genome (UCSC hg19) as previously described ¹. Each variant was annotated with respect to gene location and predicted function in HGVS nomenclature. Deletions and duplications of exons were detected by a combination of depth of coverage and split read analysis, as previously described ¹⁵. All frameshift, nonsense, splice site and missense mutations predicted to be deleterious to protein function were validated by PCR amplification and Sanger sequencing. Missense mutations and in-frame deletions were classified as deleterious only if a specific functional assessment could be or previously had been carried out. For mutations in Lynch-associated genes, microsatellite instability and MLH1 promoter methylation was assessed, as previously described ¹³.

RESULTS

Subjects were women with endometrial carcinoma designated as serous histology (either purely serous or mixed). The series was unselected for family history or any clinical features suggestive of a genetic predisposition to cancer. One hundred fifty-one subjects with pure serous or mixed histology were included in the study. Table 2 provides clinical and pathological characteristics of the study population. An additional ten subjects with <10% serous histology were also included in a separate analysis.

Table 2.

Subject characteristics

Median age at diagnosis	68 years
Stage*
I	n=61 (40%)
II	n=16 (11%)
III	n=34 (23%)
IV	n=38 (25%)
Unstaged	n=2 (1%)
Histology
100% UPSC	n=74 (49%)
Mixed	n=77
≥50% serous	n=31 (21%)
<50% serous	n=46 (30%)
Race
Caucasian	n=100 (66%)
African American	n=39 (26%)
Asian	n=1 (1%)
Other	n=3 (2%)
Unknown	n=8 (5%)

^*FIGO 2009 staging guidelines

Seven of 151 subjects (4.6%) had germline loss-of-function mutations in three genes. No subject had more than one mutation. Deleterious mutations included three in BRCA1 (2%), two in CHEK2 (1.3%), and two in TP53 (1.3%, Table 3). In addition, of the ten subjects with <10% serous histology, one subject had a deleterious MSH6 mutation. Characteristics of USC cases with a mutation are detailed in Table 3. The mutations were similarly distributed between cases of pure and mixed histology, with three mutations in subjects with pure USC and four in mixed USC. The median age of cancer diagnosis in mutation carriers was 65 years, not significantly different than the median age of 68 years for all USC subjects.

Table 3.

Characteristics of mutation carriers

Mutation	Mutation type	Age at diagnosis (yrs)	Ethnicity	Histology	Stage	Personal history of other cancers	Family history of cancer
BRCA1 p.E1535X	Nonsense	38	African-American	Mixed (endometrioid, serous)	IIIA	Breast cancer (age 37)	Two paternal aunts with breast cancer (ages 45, 53), maternal half-brother with leukemia (age 16), maternal grandfather with lung cancer (age 67)
BRCA1 c.2594delC	Frameshift	67	Caucasian	100% UPSC	IA	Synchronous ovarian cancer (age 67), breast cancer (age 50)	Sister with breast cancer, another sister with ovarian cancer
BRCA1 c.713-2A>C	Splice site†	66	Caucasian	100% UPSC	IB	Esophageal cancer (age 74)	Daughter with cervical cancer
TP53 p.R290H	Missense‡	48	Caucasian	Mixed (endometrioid, serous)	IIIC1	None	Father with lymphoma (age 39), grandmother with multiple myeloma
TP53 p.R273H	Missense‡	77	Caucasian	100% UPSC	IVA	Unknown	Unknown
CHEK2 c.1100delC	Frameshift	79	Caucasian	Mixed (endometrioid, serous)	IVA	Colon cancer	None
CHEK2 p.I157T	Missense⋄	64	Caucasian	Mixed (clear cell, serous)	IA	None	Son with ependymoma, father with prostate cancer

^†previously demonstrated to be damaging (http://research.nhgri.nih.gov/bic/)

^‡previously demonstrated to be damaging (http://www-p53.iarc.fr/)

^⋄previously demonstrated to be damaging¹⁷

The frequency of BRCA1 germline loss-of-function mutations in subjects with USC was 2% (95% CI = 0.7% to 5.7%). All three BRCA1 mutations identified have been previously reported (http://research.nhgri.nih.gov/bic/), but none were Ashkenazi founder mutations (Table 3). Two of the three subjects with deleterious BRCA1 mutations had personal histories of breast carcinoma and both had significant family histories of breast and/or ovarian carcinoma. Out of 134 USC subjects with personal and family history data available, 22 (16.4%) had a personal history of breast carcinoma, and 40 (29.9%) had family histories of breast and/or ovarian carcinoma. Of the 22 women with USC and a personal history of breast carcinoma, the frequency of BRCA1 mutations was 9% (95% CI = 3 to 28%), compared to 0.9% in 112 women with no such history (p=0.07, Table 4). Only clearly deleterious germline mutations were included in our total mutation rate. Additionally, thirty-six uncommon non-synonymous missense variants (<1% frequency rate reported on the Exome Variant Server (EVS), http://evs.gs.washington.edu/EVS/, March 30, 2012) were detected in BRCA1/2 (Table 5), 12 of which are reported as benign on the breast cancer information core database (BIC), http://research.nhgri.nih.gov/bic/, March 30, 2012. Only one of these missense variants, BRCA2 p.K912Q, had not been previously reported on either EVS or BIC. BRCA2 p.K912Q was predicted to be possibly damaging by Polyphen2, and benign by SIFT.

Table 4.

Studies of USC and BRCA1/2 mutations

Study	Number of USC subjects	Population	Mutation ascertainment	BRCA1 mutations	BRCA2 mutations	Personal history of breast cancer	BRCA1/2 in breast cancer subjects	BRCA1/2 in non-breast cancer subjects
Biron-Shental et al.5	22	Israeli Jewish	Ashkenazi founder mutations	3 (13.6%)	3 (13.6%)	7 (31.8%)	3 (42.9%)	3 (20%)
Levine et al.6	17	Ashkenazi Jewish	Ashkenazi founder mutations	0	0	Not available	Not available	Not available
Lavie et al.7	59	Ashkenazi Jewish	Ashkenazi founder mutations	7 (11.9%)	1 (1.7%)	15 (25.4%)	3 (20%)	5 (11.4%)
Goshen et al.8	56	Canadian	Selected founder mutations and protein truncation test	0	0	6 (10.7%)	0	0
Current series	151	American	Comprehensive analysis	3 (2.0%)	0	22 (16.4%) †	2 (9.1%)	1 (0.9%)*

^†out of 134 subjects with personal history data available

^*out of 112 subject without a history of breast carcinoma

Table 5.

Uncommon non-synonymous missense mutations detected in BRCA1 and BRCA2.

Gene	Variant*	Reported on BIC	EVS EA allele freq	EVS AA allele freq	Polyphen2	SIFT
BRCA1	p.T1561I	uncertain significance	0/7020	20/3718	0.988	0
BRCA1	p.R1347G	uncertain significance	42/6978	4/3734	0.255	0.01
BRCA1	p.P1238L	uncertain significance	1/7019	0/3736	0.264	0.06
BRCA1	p.N723D	uncertain significance	0/7020	26/3710	0.164	0.1
BRCA1	p.L512F	uncertain significance	not reported	not reported	1	0
BRCA1	p.H476R	uncertain significance	0/7020	9/3729	0.97	0.07
BRCA1	p.V1534M	uncertain significance	2/7018	14/3724	0.07	0.22
BRCA1	p.S1512I	benign	19/7001	3/3735	0.741	0
BRCA1	p.R1347G	uncertain significance	42/6978	4/3734	0.255	0.01
BRCA1	p.M1008V	benign	0/7020	8/3728	0	0.78
BRCA1	p.K912Q	not reported	not reported	not reported	0.492	0.45
BRCA1	p.H476R	uncertain significance	0/7020	9/729	0.97	0.07
BRCA1	p.D214G	uncertain significance	1/7019	0/3736	0.001	0.34
BRCA2	p.T598A	benign	11/7001	3/3735	0.001	0.92
BRCA2	p.D935N	benign	6/7010	1/3737	0.055	0.21
BRCA2	p.R1190Q	uncertain significance	not reported	not reported	0	1
BRCA2	p.D1420Y	benign	42/6932	5/3661	0.03	0
BRCA2	p.G1529R	benign	3/7017	0/3738	1	0
BRCA2	p.V1639I	uncertain significance	not reported	not reported	0.09	0.14
BRCA2	p.K1690N	uncertain significance	2/6994	0/3964	0.989	0.13
BRCA2	p.S1733F	uncertain significance	1/7005	12/3718	0.159	0.01
BRCA2	p.E1879K	uncertain significance	2/7018	0/3738	0.068	0.54
BRCA2	p.R2034C	uncertain significance	35/6983	9/3729	0.556	0.16
BRCA2	p.H2116R	benign	4/7010	34/3704	0.971	0.29
BRCA2	p.Q2384K	uncertain significance	0/7020	22/3716	0	1
BRCA2	p.E2856A	benign	13/7007	2/3736	0.981	0.15
BRCA2	p.A2951T	benign	45/6975	5/3733	1	0.03
BRCA2	p.T225A	uncertain significance	not reported	not reported	0.41	0.12
BRCA2	p.N987I	benign	0/7006	37/3701	0.744	0.08
BRCA2	p.D1420Y	benign	42/6932	5/3661	0.03	0
BRCA2	p.G1529R	benign	3/7019	0/3738	1	0
BRCA2	p.H1561N	uncertain significance	0/7020	36/3702	0.665	0.28
BRCA2	p.R2034C	uncertain significance	35/6983	9/3729	0.556	0.16
BRCA2	p.V2138F	uncertain significance	0/7000	33/3699	0.255	0.08
BRCA2	p.K2729N	uncertain significance	not reported	not reported	1	0.07
BRCA2	p.D3272E	uncertain significance	not reported	not reported	0.981	0.13

^*using RefSeq NM_007294.3 for BRCA1 and NM_000059.3 for BRCA2

BIC: Breast cancer information core database (http://research.nhgri.nih.gov/bic/), EVS: Exome variant server (http://evs.gs.washington.edu/EVS/)

Two subjects had deleterious TP53 mutations (1.3%). Both of the TP53 mutations identified in our study subjects have been previously reported in Li-Fraumeni syndrome (LFS) families (http://www-p53.iarc.fr/). One mutation carrier had mixed USC and the other had pure USC. The R290H mutation carrier did not have a family history suggestive of LFS, although her family history was notable for a father with lymphoma at age 39 and a grandmother with multiple myeloma. The R290H mutation has been reported in multiple LFS families, although it has a weak mutant phenotype when assessed in functional assays¹⁶. No family history data was available for the subject with the R273H mutation.

Two subjects had mutations in CHEK2 (1.3%), both cases with mixed USC. One mutation was the CHEK2 c.1100delC founder mutation, and the other mutation, p.I157T, is a missense mutation that has been demonstrated to be damaging through functional assays ¹⁷.

A single DNA mismatch repair gene mutation was identified in a subject with an endometrioid tumor with 1% serous histology. The in-frame deletion MSH6 deletion was classified as deleterious given the tumor microsatellite instability-high (MSI-H) phenotype (defined by having instability in two or more of the following markers: BAT25, BAT26, D5S346, D2S123, and D17S250) and lack of MLH1 promoter methylation. The mutation carrier did not have a family history of cancer and did not meet Amsterdam criteria for Lynch syndrome.

DISCUSSION

This is the first study to comprehensively evaluate an unselected USC population for germline mutations in 30 tumor suppressor genes, including BRCA1, BRCA2, the DNA mismatch repair genes, TP53, and genes in the Fanconi-anemia (FA)-BRCA pathway. USC represents only 10% of all endometrial carcinoma cases ²; thus, 151 USC cases represent a large series of this relatively rare cancer sub-type. Subjects were not selected for age or family history, in an effort to obtain an unbiased mutation rate in the general population. However, both institutions represented in this study are tertiary referral centers, and it is possible that the mutation rate reported here may be influenced by a referral bias for patients with personal and family histories of cancer.

We and others have previously identified germline mutations in 11 different genes in the FA-BRCA pathway in subjects with ovarian carcinoma ^{1, 18–20}. In contrast, in USC, only BRCA1 and CHEK2 have significant rates of germline mutations from the FA-BRCA pathway, suggesting that the FA-BRCA pathway is less widely implicated in USC compared to ovarian carcinoma. Thus, although USC and serous ovarian carcinoma share many pathological and clinical features, the molecular epidemiology of USC does differ from that of ovarian carcinoma.

Our data reveal that approximately 2% of unselected women with USC have a germline BRCA1 mutation. Although the overall mutation rate is low, it is higher than would be expected in the general population, in which BRCA1 mutation frequency has been estimated at approximately 0.06% ²¹. Two of the three mutation carriers had personal histories of breast carcinoma and family histories of breast/ovarian carcinoma. The rate of BRCA1/2 mutations in women with USC and prior breast carcinoma in this series was 9%, suggesting that women with USC and prior breast carcinoma should be offered genetic testing for BRCA1 and BRCA2 mutations. These data support the conclusion that USC is associated with hereditary breast and ovarian cancer, albeit in a small proportion of cases. While our findings suggest an elevated relative risk of USC in BRCA1 mutation carriers, the absolute risk is likely to be small, given the rarity of USC in the general population. Whether these data should influence the role of hysterectomy in combination with risk-reducing salpingo-oophorectomy for cancer prevention in BRCA1 mutation carriers requires further study.

Four smaller studies have explored the association of USC with germline BRCA1 or BRCA2 mutations, with conflicting results (summarized in Table 4) ^5–8. In the only other non-Ashkenazi series, Goshen et al. studied 56 Canadian women with USC and failed to detect any BRCA1 or BRCA2 mutations, but used non-comprehensive testing, which would have missed two of the three BRCA1 mutations identified in our study ⁸. Three previous studies were in Jewish populations and tested only for the three Ashkenazi founder mutations. Two of the three Jewish studies found an increased mutation rate in BRCA1 and BRCA2 (14–27%, compared to an expected 2.3% founder mutation rate) ^{5, 7}, while the smallest series of 17 subjects found no mutations ⁶. Interestingly, the largest Ashkenazi series by Lavie et al. found a significantly higher mutation rate in BRCA1 (11.9%) than in BRCA2 mutations (1.7%, Table 4) ⁷. Though the number of mutations in our series is small, all occurred in BRCA1. In combining data from all the series on USC, there were 13 BRCA1 mutations in 305 cases compared to 4 BRCA2 mutations (p=0.046, Fishers Exact test). Therefore, it may be that USC is more commonly associated with mutations in BRCA1 than BRCA2. The association of BRCA1/2 mutations in endometrial carcinomas appears limited to USC, as the one large series of 199 mostly endometrioid endometrial carcinoma in Ashkenazi women did not find a mutation rate different than the expected population frequency ⁶.

The 1.3% rate of TP53 mutations seen in this study was unexpected, as uterine carcinoma is not a known manifestation of Li-Fraumeni syndrome. However, the neoplastic spectrum in TP53 mutation carriers is much wider than the specific cancers used to define Li-Fraumeni syndrome (LFS)/Li-Fraumeni-like syndrome (LFL), with roughly 20–30% of cancers in TP53 mutation-positive families falling outside the classic spectrum ^23–25. Both of the specific TP53 mutations in our subjects have been previously reported in LFS families (IARC TP53 database R15, November 2010, http://www-p53.iarc.fr/). Only one TP53 mutation carrier had available family history information, and she did not fit criteria for either LFS or LFL. This finding is similar to our previous observations of deleterious TP53 mutations in women with ovarian carcinoma ¹. Of several studies exploring the wide spectrum of cancers in LFS/LFL families, one reported endometrial carcinoma as a rare finding ²⁵. In some families with TP53 mutations, there may be a wider range of cancer types, lower cancer risk, and later onset of tumors, suggesting that deleterious TP53 mutations may be more frequent in the population than previously assumed. Such families with reduced penetrance and later average age of onset might go unnoticed due to the generally restrictive guidelines used for TP53 mutation testing. As comprehensive genetic testing is increasingly offered to individuals not selected for established syndromic phenotypes or family history, a wider range of expressivity associated with germline mutations of cancer susceptibility genes may become increasingly apparent.

Our data suggest that the rate of Lynch syndrome in subjects with USC is lower than that of endometrioid carcinomas (1.8–2.1%) ^{11, 12}. No USC subjects included in our primary analysis were found to have germline mutations in any of the mismatch repair genes. Of the additional ten subjects with <10% serous histology analyzed, one had a germline mutation in MSH6, Interestingly, this one case with the MSH6 mutation contained only 1% serous and 99% endometrioid components.. Although USC has been previously reported in subjects with Lynch syndrome, no prior studies specifically evaluated for germline mutations in the mismatch repair genes in a series of USC. Our findings are concordant with a recent study demonstrating no defects in DNA mismatch repair in the neoplastic DNA from 29 pure or mixed USC cases ²². In that study, pancreatic carcinomas were overrepresented in relatives of individuals with USC, but this excess was not explained by DNA mismatch repair defects. We speculate that BRCA1 or BRCA2 mutations could serve as the common link between USC and pancreatic cancer in these families.

Overall, 5% of USC cases had germline loss-of-function mutations in three of 30 tumor suppressor genes evaluated. Mutations in DNA mismatch repair genes that cause Lynch syndrome are rare in USC, similar to the rate for ovarian carcinoma. The germline BRCA1 mutation rate in USC subjects of 2% is higher than expected in a non-founder population, suggesting that USC is associated with hereditary breast and ovarian cancer in a small proportion of cases. In contrast, USC is less likely to be associated with mutations in other FA-BRCA genes compared to ovarian carcinoma.