Cancer risk and overall survival in APC I1307K carriers.

Abstract

1592 Background: The germline variant APC I1307K is one of the most commonly identified pathogenic variants on germline genetic testing panels. The purpose of the Molecular Epidemiology of Colorectal Cancer study was to quantify the risk of colorectal cancer among carriers, characterize the clinical, pathologic, and molecular features of colorectal cancers arising in patients with APC I1307K, and to describe the overall and disease-specific survival of carriers with colorectal cancer. Here, the final results of the Molecular Epidemiology of Colorectal Cancer Study are reported with respect to APC I1307K. Methods: We consented 6,006 incident, pathologically confirmed cases of colorectal adenocarcinoma and 5,023 age, sex, and ethnicity matched controls without colorectal cancer between March 31, 1998 and July 1, 2017 within a geographically defined area of Northern Israel. Comprehensive, in-person epidemiologic interviews were conducted for cases and controls, with uniform histopathologic review, detailed molecular analysis, medical record review and clinical follow-up for up to 21 years. Results: The demographic and clinical features of incident colorectal cancer cases matched the population distribution of colorectal cancer in Israel. APC I1307K was identified in 429 (7.1%) of cases and 201 (4.0%) of controls. The estimated relative risk of colorectal cancer among carriers was 1.89 (95% confidence interval, 1.59 - 2.24), p < 0.0001. The prevalence and odds ratios differed by ethnic group. Homozygous carriers were at especially high risk, with an odds ratio of 3.90 (95% confidence interval 1.11–13.71). APC I1307K carriers were significantly less likely to have microsatellite instable tumors (p = 0.04). Overall survival of APC I1307K carriers was not significantly different than survival of non-carriers, after adjustment for age, stage, sex, ethnicity, and microsatellite instability. Conclusions: APC I1307K is an actionable germline mutation that confers meaningful lifetime risk of colorectal cancer in heterozygous and homozygous carriers. APC I1307K is not an independent prognostic factor for overall survival or disease specific survival and is not associated with the MSI phenotype. Cumulative lifetime risk estimates inform genetic counseling and provide data for policies regarding the timing and frequency of screening and other preventive strategies.