Mucins in the colorectal neoplastic spectrum with reference to conventional and serrated adenomas

Alterations in expression of mucins and aberrant expression of various types of mucin genes were observed in colorectal adenomas and carcinomas, though their significance in neoplastic transformation of colorectal epithelium is yet to be determined. The aim of this study was to determine expression of MUC1, MUC2, MUC5AC, and MUC6 through conventional adenoma-carcinoma sequence and polyps involved in the "serrated" pathway of the colorectum using tissue array technique.

In this study, a total of 172 cases including 100 colorectal polyps [8 hyperplastic polyps, 10 sessile serrated adenomas, 19 tubular, 37 tubulovillous, and 26 villous adenomas], 16 adenomas with intramucosal carcinoma, 28 conventional colorectal cancers, and 28 normal mucosae were examined. Tissue array blocks were prepared and sections were stained immunohistochemically for MUC1, MUC2, MUC5AC, and MUC6.

Expression of MUC1 significantly increased in close correlation with the neoplastic process and reached its highest values in intramucosal carcinomas and conventional colorectal cancers (p<0.001). In contrast, MUC2 expression showed a significant decrease in intramucosal carcinoma and conventional colorectal cancer groups (p<0.001). Sessile serrated adenomas exhibited the highest MUC5AC expression while adenomatous polyps showed an increase in MUC5AC expression in parallel with neoplastic progression (p<0.001). Hyperplastic polyps seemed to lie between normal mucosa and sessile serrated adenomas in terms of mucin expression, suggesting that they are morphologically and histogenetically linked.

Upregulation of MUC1 and MUC6 through the adenoma-carcinoma sequence together with downregulation of MUC2 and MUC5AC at the neoplastic end of the spectrum seem to follow the steps of malignant transformation.