An immunohistochemical comparison of cytokeratin 7, cytokeratin 15, cytokeratin 19, CAM 5.2, carcinoembryonic antigen, and nestin in differentiating porocarcinoma from squamous cell carcinoma.

The distinction of porocarcinoma from squamous cell carcinoma is clinically relevant but can often be a diagnostic dilemma. Current markers reported to be helpful in diagnosing porocarcinoma include carcinoembryonic antigen and cytokeratin 7; however, their expression has been demonstrated in 30% to 80% and 13% to 22% of squamous cell carcinoma cases, respectively. In this study, we assessed immunohistochemical expression of cytokeratin 7, cytokeratin 15, cytokeratin 19, CAM 5.2, carcinoembryonic antigen, and nestin in 67 cases (39 porocarcinomas and 28 moderately differentiated squamous cell carcinomas) to determine their use as histologic adjuncts. Expression of carcinoembryonic antigen, cytokeratin 19, cytokeratin 7, CAM 5.2, cytokeratin 15, and nestin was seen in 77%, 67%, 64%, 51%, 49%, and 13% of porocarcinomas, respectively; and in 57%, 18%, 26%, 32%, 30%, and 37% of squamous cell carcinomas, respectively. Of these, cytokeratin 19 was the most specific (specificity, 82%) in detecting porocarcinomas, and carcinoembryonic antigen was the most sensitive (sensitivity, 77%). By χ(2) test, statistically significant P values (<.05) were observed for cytokeratin 7, cytokeratin 19, and nestin in the distinction of porocarcinoma from squamous cell carcinoma. However, in a logistic regression and stepwise selection for predicting a porocarcinoma, statistical significance was observed only for cytokeratin 19 (P = .0003). In conclusion, we found cytokeratin 19 to be a helpful marker in the distinction of porocarcinoma from squamous cell carcinoma, although a focal staining pattern can be seen in a third of cases. The diagnostic sensitivity and specificity appear to be significantly improved using a selected panel of immunohistochemical stains that include cytokeratin 7, cytokeratin 19, and nestin.