B-210 Spectrum of Germline Mutation with Characteristic MLH1 Hotspots and High Concordance with MMR Deficiency Phenotype in Lynch Syndrome Patients in Taiwan

Abstract

Abstract Background Patients carried defects on cancer susceptibility genes or had cancer family history have at least twice the risk of developing cancer than the general population, with both early onset and multiple cancers features. For elucidating the carrier rate of cancer susceptibility genes in patients with inherited colorectal cancer (CRC) and endometrial cancer (EnCa) in Taiwan, we established a NCCN guided 30-gene panel which included four DNA Mismatch Repair (MMR) genes to detect the germline mutation of patients with Lynch Syndrome. Correlation of genotype and phenotype of MMR enzymes are under investigation as well. Methods Sixty-eight blood samples were collected from unrelated cancer patients, 42 of them were from patients with inherited colon cancer, 13 from patients with diagnosis of both CRC and endometrial cancer and 13 from patients with early onset EnCa. 30-gene panel was performed by next generation sequencing (NGS) platform and variants were annotated following ACMG guideline. MMR protein expression in tumor tissue sections were identified by conventional immunohistochemistry (IHC) stain. Loss of nuclear staining were classified as MMR deficiency. Results Average age of first tumor onset of 68 patients were 49.2 years old. 54% (37/68) of the subjects had at least one germline mutations with pathogenic effect or deleterious variant predicted by in silico protein function software. Five of them carried two heterozygous mutations. Total 42 mutations appeared majority on three MMR genes, MLH1 (17/42, 40%), MSH2 (10/42, 24%) and MSH6 (6/42, 11%) with notified three hotspots on MLH1 p.R265C (7/17, 41%); p.T117M (2/17, 12%) and p.K618del(2/17, 12%). The rest mutations spread sporadically on nine genes (PMS2, TP53, CHEK2, POLE, POLD1, ATM, EPCAM, MLH3 and RNF43). For exploring the effect of germline mutation on MMR protein expression status on tissue, we compared the MMR IHC results and the germline mutation pattern. As high as 57% concordance between phenotype and genotype were found. We also collected six blood samples from relatives of our CRC cohort to demonstrate the inheritance and pathogenesis of the germline mutation. Exactly the same germline mutations can be found in diseased relatives among different generation or siblings. Conclusion In spite of having founder mutations on MLH1 gene in Taiwanese Lynch syndrome, most of the germline mutations randomly occurred in MMR-related genes. Comprehensive cancer susceptible gene screening panel by NGS is a cost-effective way to identify the inherited status of individuals with family cancer history and serves as a surrogate tool to predict MMR protein expression. Genetic counseling and prophylactic therapeutic information can be provided for positive cases for better cancer prevention.