Germline drivers of gynecologic carcinosarcomas.

Objectives: To describe the prevalence of germline pathogenic variants (gPVs) in endometrial and ovarian carcinosarcomas and determine if gPVs are drivers of carcinosarcoma.

Methods: Patients with endometrial or ovarian carcinosarcomas who underwent clinical tumor-normal sequencing from 1/1/2015 to 6/1/2021 and consented to germline assessment of ≥76 cancer predisposition genes were included. In patients with gPVs, biallelic inactivation was identified through analysis of loss of heterozygosity and somatic pathogenic alterations.

Results: Of 216 patients identified, 167 (77%) were diagnosed with endometrial carcinosarcoma and 49 (23%) with ovarian carcinosarcoma. Overall, 33 gPVs were observed in 29 patients (13%); 20 gPVs (61%) had biallelic loss in tumors. The rate of high-penetrance gPVs overall was 7% (16 of 216); 88% of high-penetrance gPVs had biallelic loss. In the endometrial carcinosarcoma cohort, 22 gPVs were found in 19 (11%) of 167 patients; 12 gPVs (55%) had biallelic loss in tumors, including 8 (89%) of 9 in high-penetrance gPVs. Among the ovarian carcinosarcoma cohort, 11 gPVs were found in 10 (20%) of 49 patients; 8 gPVs (73%) had biallelic loss in tumors, and all evaluable high-penetrance gPVs (n = 6) had biallelic loss. All gPVs in homologous recombination (BRCA1, BRCA2, RAD51C) and Lynch syndrome (MSH2, MSH6) genes had biallelic loss in tumors (n = 15).

Conclusions: gPVs in genes affecting homologous recombination- or Lynch-associated mismatch repair exhibited biallelic inactivation within tumors, suggesting likely drivers of gynecologic carcinosarcoma. Our data support germline testing for patients with gynecologic carcinosarcomas, given implications for treatment and risk-reduction in patients and at-risk family members.