Surgical phenotype of patients with peritoneal mesothelioma and a germline mutation.

BACKGROUND: This study aimed to investigate if peritoneal mesothelioma (PM) patients with germline mutations (GM) have distinct surgical characteristics when compared to those without GM. METHODS: PM patients were selected from an ongoing prospective study that conducts germline testing of 82 susceptibility genes. Germline status was correlated with surgical data obtained from a prospectively collected database using univariate, multivariate, and receiver operating characteristic (ROC) analyses. RESULTS: Out of 88 PM patients enrolled between 2009 and 2019, 18 GMs (20.5%) were identified in BRCA1-associated protein 1 (BAP1) (n = 11, 12.5% of all patients), SDHA (n = 2) and WT1, CDKN2A, CHEK2, ATM, and BRCA2 (n = 1 patient each). Surgical procedures were performed in 71 patients, the most common of which were cytoreductive surgeries with hyperthermic intraperitoneal chemotherapy (n = 61). Patients with GM presented with a higher prevalence of other prior cancers (61.1% vs. 31.4%, p = .02) and lower platelet count (251 [160-413] vs. 367 [196-780] K/µL, p = .005) compared to those without GM (n = 70). Survival outcomes did not differ significantly between the groups. Patients with BAP1 GMs were more likely to develop bicavitary disease and to present with lower platelet count and mitotic count score, and higher peritoneal cancer index (PCI, all p ≤ .04) compared with those without GM. On ROC analysis, the combination of PCI, platelet count and mitotic score yielded an area under the curve of 0.96 (95% CI, 0.91-1.0) for BAP1 GM detection among operated PM patients. CONCLUSION: Higher intraoperative tumor burden and lower platelet count and mitotic score are suggestive of BAP1 GMs in surgical PM patients and should prompt germline testing.

Germline Variants Incidentally Detected via Tumor-Only Genomic Profiling of Patients With Mesothelioma.

Importance: Patients with mesothelioma often have next-generation sequencing (NGS) of their tumor performed; tumor-only NGS may incidentally identify germline pathogenic or likely pathogenic (P/LP) variants despite not being designed for this purpose. It is unknown how frequently patients with mesothelioma have germline P/LP variants incidentally detected via tumor-only NGS. Objective: To determine the prevalence of incidental germline P/LP variants detected via tumor-only NGS of mesothelioma. Design, Setting, and Participants: A series of 161 unrelated patients with mesothelioma from a high-volume mesothelioma program had tumor-only and germline NGS performed during April 2016 to October 2021. Follow-up ranged from 18 months to 7 years. Tumor and germline assays were compared to determine which P/LP variants identified via tumor-only NGS were of germline origin. Data were analyzed from January to March 2023. Main Outcomes and Measures: The proportion of patients with mesothelioma who had P/LP germline variants incidentally detected via tumor-only NGS. Results: Of 161 patients with mesothelioma, 105 were male (65%), the mean (SD) age was 64.7 (11.2) years, and 156 patients (97%) self-identified as non-Hispanic White. Most (126 patients [78%]) had at least 1 potentially incidental P/LP germline variant. The positive predictive value of a potentially incidental germline P/LP variant on tumor-only NGS was 20%. Overall, 26 patients (16%) carried a P/LP germline variant. Germline P/LP variants were identified in ATM, ATR, BAP1, CHEK2, DDX41, FANCM, HAX1, MRE11A, MSH6, MUTYH, NF1, SAMD9L, and TMEM127. Conclusions and Relevance: In this case series of 161 patients with mesothelioma, 16% had confirmed germline P/LP variants. Given the implications of a hereditary cancer syndrome diagnosis for preventive care and familial counseling, clinical approaches for addressing incidental P/LP germline variants in tumor-only NGS are needed. Tumor-only sequencing should not replace dedicated germline testing. Universal germline testing is likely needed for patients with mesothelioma.