Co-expression of gastric and biliary phenotype in pyloric-gland type adenoma of the gallbladder: immunohistochemical analysis of mucin profile and CD10.

Pyloric-gland type adenoma of the gallbladder is formed by proliferation of glands resembling pyloric glands, morphologically. No previous report has described the cellular phenotype and differentiation of pyloric-gland type adenoma of the gallbladder, using CD10 as a marker of proper biliary phenotype. Immunostainings were performed for mucin markers such as MUC5AC, human gastric mucin (HGM) for gastric foveolar type epithelium, MUC6, M-GGMC-1 for pyloric-gland type and MUC2 for intestinal goblet-cell type, and for CD10 as a proper biliary type marker on 58 pyloric-gland type adenomas of the gallbladder, as well as for p53, Ki-67 and CDX2. The percentage (X) of reactive cells in relation to the total number of tumor cells was estimated semi-quantitatively, and divided into four categories: X=0% (negative), 0%<X<10%, 10%<or=X<30%, and X>or=30%. CDX2 expression was considered to be positive when the percentage of positively stained cells was >or=10%. Out of the 58 pyloric-gland type adenomas, >or=30% of adenoma cells were positive for MUC5AC in 22 (38%) tumors, HGM in 29 (50%), MUC6 in 58 (100%), M-GGMC-1 in 54 (93%), MUC2 in none (0%), and CD10 in 20 (34%). MUC6 (P<0.001) and M-GGMC-1 (P<0.001) mucins were detected more frequently in pyloric-gland type adenomas, and CD10 expression was significantly decreased, compared with normal gallbladder epithelium (P=0.006). P53 overexpression was not found in any of the 58 tumors, including two adenomas with carcinomatous foci. The mean number of Ki-67-positive cells was 10.3+/-5.8%. CDX2 expression was judged as negative in all 58 pyloric-gland type adenomas. In pyloric-gland type adenomas of the gallbladder, expression of pyloric-gland type mucins was observed with a high frequency, whereas intestinal goblet-cell mucins were rarely seen. In addition, co-expression of gastric foveolar type mucins and CD10 was also demonstrated. Pyloric-gland type adenomas of the gallbladder show a differentiation toward pyloric glands in terms of immunohistochemistry, as well as morphology, accompanied by co-expression of gastric foveolar and native biliary phenotypes.