Evaluating the clinical utility of universal screening to identify Lynch syndrome in stage III/III colorectal cancer patients: A prospective observational study in Japan.

Abstract

41 Background: Universal screening for Lynch syndrome (LS) by identifying deficient DNA mismatch repair (MMR) in the tumor tissue of all new colorectal cancer (CRC) patients is widely accepted. The population prevalence of LS is approximately 3% in Western countries, whereas it is approximately 0.7% in Japan. In addition, the number of relatives diagnosed per proband is 3.6 in Western countries, whereas there are even fewer diagnoses per proband in Japan. To address the issue of LS remaining largely underdiagnosed in Japan, we prospectively evaluated the clinical utility of universal screening of LS in CRC patients. Methods: From March 2016 to August 2019, all consecutive new cases of stage II/III CRC underwent immunohistochemistry (IHC) screening for MMR using MLH1, MSH2, MSH6, and PMS2 antibodies. The patients negative for both MLH1 and PMS2 (MLH1-/PMS2-) were subjected to reflex testing for BRAF V600E mutation. Patients with both MLH1-/PMS2- and BRAF negative (cohort A, n = 14) and those with other IHC patterns (cohort B, n = 13) were referred for genetic counseling (GC) and genetic testing (GT). Furthermore, relatives of probands with confirmed LS were referred for GC/GT if they were willing. Results: Overall, 591 pts were enrolled in this study. Patient background were as follows: > 70 y/o, 35%; right-sided/left-sided colon/rectum, 24%/24%/53%; and cStage II/III, 65%/35%. Of 591 patients, 40 (6.8%) had MMR deficiency. Of 27 patients with MLH1-/PMS2-, 24 underwent BRAF reflex testing; only 10 of these patients tested positive for mutation. Of 27 patients recommended for GC, 25 were referred for GC and 22 for GT, which revealed 12 LS cases (2%, mutation genes:MLH1/PMS2/MSH2; 4/2/6). The frequency of LS diagnosis with respect to patient background was as follows: > 70/≤70 y, 1.0/2.6%; right-sided/left-sided colon/rectum, 5.8/0/1.3%; and cStage II/III, 2.6/1.0%. Interestingly, only 3 (25%) of 12 patients who underwent GC/GT in cohort A had LS compared with 9 (90%) of 10 patients in cohort B ( p= 0.004). Moreover, among 11 relatives of 5 families who were willing to undergo GC/GT, six (55%) had LS, of whom two were first-degree relatives (33%), one was a second-degree relative (50%), and three were third-degree relatives (100%). Conclusions: This study showed that universal screening of LS in CRC patients is significantly useful in Japan. Furthermore, implementing a reflex testing strategy demonstrated high adherence to guidelines and the appropriateness of our referrals for GC/GT.