Mucin core protein expression by colorectal mucinous carcinomas with or without mucus hyperplasia

Background. In the categorization of colorectal mucinous carcinomas, much attention has been paid to the amount of extracellular mucin, but little to that of intracellular mucin. Perhaps this factor would be useful in further categorization. Methods. We estimated the amount of intracellular mucin morphologically, and classified colorectal tumors (tubular adenomas, mucinous carcinomas, and nonmucinous carcinomas) into two categories each, those with and without intracellular mucus hyperplasia. From preliminary results, we chose a range of 50% or more for the ratio of intracellular mucus to the total area of tumor cells for our definition of such hyperplasia. Then, mucin expression in the different categories was examined immunochemically with antibodies to the mucin core proteins MUC1, MUC2, MUC5AC, and MUC6. Results. MUC1 expression was found in none of the 40 adenomas, 8 (17%) of the 48 mucinous carcinomas (with little difference in those with and without mucus hyperplasia), and 4 (16%) of the 25 nonmucinous carcinomas. MUC2 was found in all mucinous carcinomas. MUC5AC was found in 18 (86%) of the 21 mucinous carcinomas with mucus hyperplasia and 18 (90%) of the 20 adenomas with mucus hyperplasia, but in only 9 (33%) of the 27 mucinous carcinomas without mucus hyperplasia, 5 (20%) of the 25 nonmucinous carcinomas, and 2 (10%) of the 20 adenomas without mucus hyperplasia. Conclusions. Mucinous carcinomas with and without mucus hyperplasia may arise from adenomas with and without mucus hyperplasia, respectively. The amount of intracellular mucin may be a morphologic reflection of the origin of colorectal mucinous carcinomas.