Unexpected germline mutations in a pan-cancer analysis including sarcoma, renal, and other cancers.

Abstract

1584 Background: Multi-gene testing for cancer predisposition is increasingly utilized in clinical care. Although the diagnostic yield and management implications of such testing in breast, ovarian and colorectal cancer are relatively well understood, data for other cancer types are still emerging. In this study we retrospectively examined 39,147 patients referred for hereditary cancer syndrome testing for pathogenic germline variants in 80 cancer risk genes, focusing on those patients with renal, sarcoma, paraganglioma, melanoma, and pancreatic cancers. Methods: Test results and personal/family history were extracted from a sequential series of de-identified clinical test reports. Data for genes not clinically ordered were analyzed under an IRB approved research protocol. Common low penetrance risk alleles were excluded. Results: Overall, 14.3% (5,589) of patients carried germline pathogenic mutations in 80 cancer risk genes. Of the 949 patients with renal cancer 20% (190) were positive, and 44% of these findings were “unexpected”, meaning they appeared in genes that are not commonly requisitioned in renal cancer patients. Of the 423 sarcoma patients, 16% (68) had positive findings, 45% of which were “unexpected”. For both cancer types, greater than 90% of these “unexpected” findings were in genes with published management recommendations. Similar results were observed in melanoma, paraganglioma and pancreatic cancer patients. A second or third pathogenic variant, many of which were also “unexpected”, were found in 3.6% of positive cases. Conclusions: In this series of patients we estimate almost 12% of pathogenic variants across cancer indications are “unexpected”. These data suggest many actionable pathogenic variants are being missed due to adherence to overly restrictive, narrowly constructed tumor-specific panels. Clinicians should expand the scope of their test panels in order to capture variants with the potential to impact patients and their family members by informing implementation of established management guidelines.