Taiwan hospital-based detection of Lynch syndrome distinguishes 2 types of microsatellite instabilities in colorectal cancers

BackgroundWith progress in techniques of molecular biology, the phenotypes and genotypes for Lynch syndrome are more diverse than thought previously. This hospital-based study estimated the incidence and molecular and clinicopathologic features of Lynch syndrome to modify the screening criteria for Taiwanese patients with colorectal cancer (CRC).MethodsA total of 561 CRC patients were enrolled. DNA was extracted from neoplasms, normal mucosa, and/or white blood cells for analyses of microsatellite instability (MSI), BRAF mutation, MLH1 methylation, and sequencing of MMR genes. Immunohistochemistry (IHC) staining for MMR proteins was done for cases that fulfilled revised Bethesda criteria and for high-frequency microsatellite instability (MSI-H) neoplasms.ResultsThere were 136 (24.2%) and 10 (1.8%) cases that fulfilled the Revised Bethesda and Amsterdam II criteria (ACII), respectively. MSI-H was detected in 41 (7.3%), of which 32 showed abnormalities for ≥1 MMR protein by IHC; low-frequency MSI (MSI-L) or microsatellite stable showed abnormal MSH2 staining in only 1 of 117 neoplasms. Thirteen (2.3%) cases had mutations in MMR genes with MLH1 (n = 10), MSH2 (n = 2), or MSH6 (n = 1). Of 13 Lynch syndrome cases, 3 (23.1%) and 11 (84.6%) fulfilled ACII and revised Bethesda criteria, respectively; 12 cases (93.3%) were MSI-H, and all had expression loss of ≥1 MMR protein. Eight patients were >50 years old, 2 of whom did not fulfill revised Bethesda criteria. For MSI-H neoplasms without definite mutations, 72.4% and 44.8% showed MLH1 methylation and a BRAF (V599E) mutation, respectively. Lynch-associated CRC and sporadic MSI neoplasms shared similar clinicopathologic features.ConclusionIn Taiwan, the incidence of Lynch syndrome was 2.3% among the 561 CRC patients evaluated. For Taiwanese CRC patients who are younger than age 60 whether or not fulfilling the Bethesda criteria should receive MSI or IHC screening for identification of the Lynch syndrome.