Assessment of Tumor Sequencing as a Replacement for Lynch Syndrome Screening and Current Molecular Tests for Patients With Colorectal Cancer

TLDR

Universal tumor screening for Lynch syndrome in colorectal cancer typically requires up to six sequential tests, and somatic gene testing is also used in stage IV disease to guide therapy. The study aims to determine whether a single upfront tumor next‑generation sequencing test can replace the current multi‑test protocol for universal Lynch syndrome screening in colorectal cancer. Tumor DNA from 465 colorectal cancer patients (419 prospective and 46 known Lynch syndrome cases) was subjected to blinded next‑generation sequencing to assess sensitivity and specificity compared with MSI, IHC, and BRAF testing. Tumor sequencing detected all 46 known Lynch syndrome cases and 12 additional cases, achieving 100 % sensitivity and 95.3 % specificity—better than MSI/IHC plus BRAF—and simultaneously identified 284 actionable KRAS/NRAS/BRAF mutations and 8 germline DPYD variants, demonstrating that a single upfront test is simpler and more sensitive than the current multi‑test approach.

Abstract

Universal tumor screening for Lynch syndrome (LS) in colorectal cancer (CRC) is recommended and involves up to 6 sequential tests. Somatic gene testing is performed on stage IV CRCs for treatment determination. The diagnostic workup for patients with CRC could be simplified and improved using a single up-front tumor next-generation sequencing test if it has higher sensitivity and specificity than the current screening protocol.To determine whether up-front tumor sequencing (TS) could replace the current multiple sequential test approach for universal tumor screening for LS.Tumor DNA from 419 consecutive CRC cases undergoing standard universal tumor screening and germline genetic testing when indicated as part of the multicenter, population-based Ohio Colorectal Cancer Prevention Initiative from October 2015 through February 2016 (the prospective cohort) and 46 patients with CRC known to have LS due to a germline mutation in a mismatch repair gene from January 2013 through September 2015 (the validation cohort) underwent blinded TS.Sensitivity of TS compared with microsatellite instability (MSI) testing and immunohistochemical (IHC) staining for the detection of LS.In the 465 patients, mean age at diagnosis was 59.9 years (range, 20-96 years), and 241 (51.8%) were female. Tumor sequencing identified all 46 known LS cases from the validation cohort and an additional 12 LS cases from the 419-member prospective cohort. Testing with MSI or IHC, followed by BRAF p.V600E testing missed 5 and 6 cases of LS, respectively. Tumor sequencing alone had better sensitivity (100%; 95% CI, 93.8%-100%) than IHC plus BRAF (89.7%; 95% CI, 78.8%-96.1%; P = .04) and MSI plus BRAF (91.4%; 95% CI, 81.0%-97.1%; P = .07). Tumor sequencing had equal specificity (95.3%; 95% CI, 92.6%-97.2%) to IHC plus BRAF (94.6%; 95% CI, 91.9%-96.6%; P > .99) and MSI plus BRAF (94.8%; 95% CI, 92.2%-96.8%; P = .88). Tumor sequencing identified 284 cases with KRAS, NRAS, or BRAF mutations that could affect therapy for stage IV CRC, avoiding another test. Finally, TS identified 8 patients with germline DPYD mutations that confer toxicity to fluorouracil chemotherapy, which could also be useful for treatment selection.Up-front TS in CRC is simpler and has superior sensitivity to current multitest approaches to LS screening, while simultaneously providing critical information for treatment selection.