Molecular Characteristics of Basaloid Squamous Cell Carcinoma of the Esophagus: Analysis of KRAS, BRAF, and PIK3CA Mutations and LINE-1 Methylation

Basaloid squamous cell carcinoma (BSCC) of the esophagus is a rare carcinoma with distinct characteristics, and was recently recognized as a variant of squamous cell carcinoma (SCC). We previously revealed genetic and epigenetic alterations associated with esophageal SCCs in relation to clinical outcome, including mutations in KRAS, BRAF, and PIK3CA, p53 expression, and long interspersed nucleotide element-1 (LINE-1) methylation, a surrogate marker for global DNA methylation level. In this study, we explored these features in BSCC. A database of 502 esophageal cancers was used to evaluate the clinical and molecular characteristics of BSCC. KRAS, BRAF, and PIK3CA mutations and LINE-1 methylation were analyzed by pyrosequencing. Of 502 tumors, 22 (4.4 %) were pathologically diagnosed as BSCC, and 440 (87 %) as SCC. No prognostic differences between BSCC and SCC cases were identified (p = 0.41). KRAS or BRAF mutations were not observed in BSCCs. While 23 % of SCC tumors harbored a PIK3CA mutation, all BSCC cases were wild-type for PIK3CA (p = 0.002), and there were no differences in p53 expression between BSCCs and SCCs (p = 0.57), as assessed by immunohistochemistry. Furthermore, BSCC tissues exhibited significantly lower levels of LINE-1 methylation than SCC tissues (p < 0.0001). These findings imply that esophageal BSCC and SCC retain different cellular phenotypes with distinct genetic and epigenetic alterations; thus, tailored therapeutic strategies should be developed against each cancer type.