Mixed colorectal polyps. An immunohistologic and mucin-histochemical study.

The morphology of mixed colorectal polyps was analysed. Thirteen such polyps were found out of 2700 colorectal polyps (0.5%). Histology showed a spectrum of hyperplastic crypts from almost pure goblet cell population (two polyps) to hypermature serrated epithelium with scanty goblet cells (seven polyps). Tubular adenomas occurred in 12 polyps, and a tubulovillous adenoma was found in the largest polyp. Moderate dysplasia was seen in the five large polyps. The border between neoplastic and hyperplastic cells was usually sharp. Mucin histochemistry showed similarities between the mixed polyps and colorectal carcinomas--namely, the reduction/absence of sialomucin in both mature hyperplastic crypts and adenomatous glands. The expression of carcinoembryonic antigen within the hyperplastic crypts and within the neoplastic crypts showing moderate dysplasia was similar to that seen in colorectal carcinomas, whereas it was normal within the neoplastic crypts with low-grade dysplasia. IgA was reduced or absent in both components. Blood group antigen was found only within the adenomatous component of the largest polyp showing also moderate dysplasia.