Phenotypic classification of gastric signet ring cell carcinoma and its relationship with K-ras mutation

We aimed to analyze gastric signet ring cell (SRC) carcinoma subtypes by investigating gastric and intestinal phenotypic marker expression, and explore the relationship between phenotype and K-ras mutation. Immunohistochemistry was performed on 163 SRC carcinoma patient specimens to detect gastric (MUC1, MUC5AC, and MUC6) and intestinal (MUC2 and CDX2) phenotypic markers, and tumors were classified into gastric (G), intestinal (I), and gastrointestinal (GI) phenotypes. DNA was extracted from the formalin-fixed, paraffin-embedded tumor samples, and K-ras mutations in codons 12, 13, and 61 were identified using polymerase chain reaction-based direct DNA sequencing. G, GI, and I phenotypes were observed in 63 (38.6%), 71 (43.5%), and 29 cases (17.8%), respectively. Expression of MUC2 was significantly associated with invasion depth and lymph node metastasis (P = 0.001 and 0.002, respectively), whereas that of CDX2 significantly corresponded to tumor size and submucosal invasion (P = 0.004 and 0.001, respectively). MUC5AC expression was inversely associated with gastric wall invasion (P = 0.001). Intestinal phenotypic marker expression was positively associated with gastric wall invasion and lymph node metastasis. K-ras mutations, all of which were in codon 12, were detected in 20 (12.27%) tumors, were significantly associated with the I phenotype, and exhibited an inverse relationship with MUC5AC and MUC6 expression. I-phenotype SRC carcinomas should be distinguished from those of the G phenotype because of their increased malignancy regarding invasion and metastasis, and higher K-ras aberration rate. The different K-ras mutation frequencies observed imply distinct genetic mechanisms in the carcinogenesis of I- and G-phenotype gastric SRC carcinomas.