Identification of a Variety of Mutations in Cancer Predisposition Genes in Patients With Suspected Lynch Syndrome

Abstract

Background & aims: Multigene panels are commercially available tools for hereditary cancer risk assessment that allow for next-generation sequencing of numerous genes in parallel. However, it is not clear if these panels offer advantages over traditional genetic testing. We investigated the number of cancer predisposition gene mutations identified by parallel sequencing in individuals with suspected Lynch syndrome.

Methods: We performed germline analysis with a 25-gene, next-generation sequencing panel using DNA from 1260 individuals who underwent clinical genetic testing for Lynch syndrome from 2012 through 2013. All patients had a history of Lynch syndrome-associated cancer and/or polyps. We classified all identified germline alterations for pathogenicity and calculated the frequencies of pathogenic mutations and variants of uncertain clinical significance (VUS). We also analyzed data on patients' personal and family history of cancer, including fulfillment of clinical guidelines for genetic testing.

Results: Of the 1260 patients, 1112 met National Comprehensive Cancer Network (NCCN) criteria for Lynch syndrome testing (88%; 95% confidence interval [CI], 86%-90%). Multigene panel testing identified 114 probands with Lynch syndrome mutations (9.0%; 95% CI, 7.6%-10.8%) and 71 with mutations in other cancer predisposition genes (5.6%; 95% CI, 4.4%-7.1%). Fifteen individuals had mutations in BRCA1 or BRCA2; 93% of these met the NCCN criteria for Lynch syndrome testing and 33% met NCCN criteria for BRCA1 and BRCA2 analysis (P = .0017). An additional 9 individuals carried mutations in other genes linked to high lifetime risks of cancer (5 had mutations in APC, 3 had bi-allelic mutations in MUTYH, and 1 had a mutation in STK11); all of these patients met NCCN criteria for Lynch syndrome testing. A total of 479 individuals had 1 or more VUS (38%; 95% CI, 35%-41%).

Conclusions: In individuals with suspected Lynch syndrome, multigene panel testing identified high-penetrance mutations in cancer predisposition genes, many of which were unexpected based on patients' histories. Parallel sequencing also detected a high number of potentially uninformative germline findings, including VUS.

Keywords: Colon Cancer Genetics; HNPCC; Hereditary Nonpolyposis Colorectal Cancer; Inherited Cancer.

Figure 1

Pathogenic mutations identified with a multigene panel among 1260 individuals with suspected Lynch syndrome. (A) Proportion of mutation carriers with Lynch syndrome mutations (purple), non-Lynch syndrome mutations (blue), or both Lynch and non-Lynch syndrome mutations (dark purple). (B) Distribution of Lynch syndrome mutation carriers by specific gene. (C) Distribution of non-Lynch syndrome mutation carriers by gene type (BRCA1/2, monoallelic MUTYH, other high-penetrance genes, or moderate-penetrance genes).

Figure 2

Number of variants of uncertain significance (VUS), per gene, detected with a multigene panel in 1260 individuals undergoing Lynch syndrome testing.