Cell proliferation in skin tumors with ductal differentiation: patterns and diagnostic applications

The kinetic features of skin tumors with ductal differentiation (TDD) remain mainly unknown. We selected 88 skin TDD (D-PAS-positive cuticles) classified according to Murphy and Elder's criteria. Tumors studied included 13 poromas, 12 nodular hidradenomas, 10 cylindromas, 6 spiradenomas, 9 syringomas, 9 chondroid syringomas, 7 porocarcinomas, 15 malignant nodular hidradenomas, and 7 not otherwise specified carcinomas. The same tumor areas were evaluated for mitotic figure counting (MFC) and proliferation rate (PR = MIB-1 index), screening 10 consecutive high-power fields (HPFs) in the most cellular areas. Results were recorded by HPF and tumor cellularity, considering both average and standard deviation. Differences were analyzed by Student's t-test and analysis of variance (ANOVA) and considered significant if p<0.05. PR was significantly higher in malignant (23.29 +/- 12.49) than in benign tumors (3.86 +/- 4.44) and in poromanodular hidradenoma (4.99 +/- 3.34) than in spiradenoma-cylindroma-syringoma (1.91 +/- 1.67), but not by malignant tumor type. MFC was significantly higher in malignant (25.52 +/- 4.10) than in benign tumors (1.57 +/- 0.38), showing porocarcinomas the biggest MFC/10 HPF and malignant nodular hidradenomas the highest MFC/1000 cells. PR and MFC are useful malignancy criteria in skin TDD and should be evaluated by tumor cellularity to avoid potential misinterpretations related with tumor heterogeneity.