Is tumour sequencing effective for the identification of germline BRCA1/2 pathogenic variant carriers?

Introduction: Tumour BRCA1/2 sequencing has progressively increased along with the expanding indications for poly(ADP-ribose) polymerase inhibitors. In our study, we investigated the feasibility and outcomes of a workflow for the identification of germline carriers based on tumour sequencing results.

Methods: Between April 2020 and December 2022, BRCA1/2 tumour testing results from 2020 patients were reviewed. Analysed tumours included: 323 ovarian, 104 breast, 314 pancreas-biliary, 87 prostate, 374 gastrointestinal, 309 lung, and 509 less common histologies. Testing was performed through small (only BRCA1/2, 16%) or comprehensive (>50 genes) next-generation sequencing panels (84%). Patients with pathogenic/likely pathogenic variants were referred for genetic counselling and germline testing.

Results: Tumour BRCA1/2 pathogenic variants were identified in 145 patients (7%). The pathogenic variant frequency ranged between 23% (75/323 ovarian) and 3.5% (11/314 pancreas-biliary). The highest frequency was observed in high-grade ovarian carcinomas (27%, 64/235). By 30 June 2023, 79 out of 145 patients (54%) underwent subsequent genetic counselling and germline testing. In these patients, mostly affected with ovarian carcinoma (67%, 53/79), 48 were confirmed germline pathogenic variants (61%).

Conclusions: In our tumour-to-germline testing approach, we observed the BRCA1/2 pathogenic variant frequency reported in other large unselected ovarian cancer cohorts, thus confirming its effectiveness in identifying putative germline carriers irrespective of eligibility for germline testing. As the range of tumours subjected to genetic testing broadens, this approach is expected to also be effective in other tumour settings for enhancing the identification of carriers, reducing the burden on genetic services, and avoiding unnecessary concerns related to germline testing.