Impact of routine mismatch repair screening on genetic counseling and surgical management in colorectal cancer patients

Abstract

Background: Mismatch repair (MMR) deficiency in colorectal cancer (CRC) should prompt consideration of genetic counseling (GC) as a Lynch syndrome (LS) diagnosis may have several implications for the patient and family. The study aims were to examine how routine MMR testing influences the rate of GC and surgical resection extent. Methods: A single-institution retrospective review was performed on CRC specimens (including colonoscopic biopsies) routinely screened for MMR deficiency from 2012 to 2018. MLH1-deficient cancers with mutated BRAF or MLH1-promoter hypermethylation were excluded. Results: MMR deficiency was identified in 295 of 1139 CRC specimens. After exclusions, 57 patients remained. Forty-two patients (74%) were identified preoperatively, and 35 (83%) were referred to GC: 16 were seen preoperatively, 9 postoperatively. Eight patients were diagnosed with Lynch syndrome (LS) preoperatively: 2 had no resection, 2 underwent segmental resection and 4 underwent extended resection. Conclusions: Most MMR–deficient patients were identified and referred to GC preoperatively, though not all were seen. Of the preoperatively diagnosed LS patients, half underwent extended resection. Barriers to GC and decision-making around resection extent bears further study.