Increased microsatellite instability and epigenetic inactivation of the hMLH1 gene in head and neck squamous cell carcinoma.

Abstract

The study is designed to elucidate the relationship between epigenetic silencing of the hMLH1 (human MutL homologue 1) gene and microsatellite instability (MSI) and the prognostic values of hMLH1 promoter methylation and MSI in head and neck squamous cell carcinoma (HNSCC). Cross-sectional study. Tertiary referral center. A total of 120 cases of HNSCC were analyzed for hMLH1 promoter hypermethylation, protein expression, and MSI by using methylation-specific polymerase chain reaction, immunohistochemical staining, and polymerase chain reaction amplification with the use of 16 fluorescent-labeled microsatellite markers, followed by fragment analysis. Of 120 HNSCCs, hMLH1 promoter hypermethylation and decreased hMLH1 protein expression were shown in 39 (32.5%) and 22 (18.3%), respectively. hMLH1 promoter hypermethylation was detected in 13 of 52 (25%) normal-appearing squamous mucosa adjacent to invasive carcinoma. MSI was detected in 21 (17.5%) tumors at two or more markers and in 99 (82.5%) tumors with no evidence of MSI or at only one marker. Hypermethylation of the hMLH1 gene is significantly associated with decreased hMLH1 protein expression (P < 0.001). High-frequency MSI was significantly associated with promoter hypermethylation (P = 0.01) but not with decreased protein expression (P = 0.069) of hMLH1 gene. hMLH1 promoter hypermethylation is significantly associated with decreased cause-specific survival for HNSCC patients (P = 0.03). Promoter hypermethylation of the hMLH1 gene could be detected early in head and neck squamous carcinogenesis and may be associated with increased MSI and poor survival in HNSCC.