Low concordance in grading atypical (dysplastic) melanocytic nevi (AMN) has been reported, and no systematic evaluation is available. We studied 123 AMN with architectural and cytologic atypia (40 associated with atypical-mole syndrome), classified according to standard criteria by 3 independent observers. Histologic variables included junctional and dermal symmetry, lateral extension, cohesion and migration of epidermal melanocytes, maturation, regression, nuclear features, nuclear grade, melanin, inflammatory infiltrate location, and fibroplasia. AMN (43 junctional and 80 compound) were graded mild (31), moderate (61), and severe (31). AMN-severe correlated with 3 or more nuclear abnormalities (especially pleomorphism, heterogeneous chromatin, and prominent nucleolus) and absence of regression, mixed junctional pattern, and suprabasilar melanocytes on top of lentiginous hyperplasia. AMN-severe diagnostic accuracy was 99.5% using these criteria, but only the absence of nuclear pleomorphism differentiated AMN-mild from AMN-moderate. No architectural features distinguishing AMN-mild from AMN-moderate were selected as significant by the discriminant analysis. AMN from atypical-mole syndrome revealed subtle architectural differences, but none were statistically significant in the discriminant analysis. Histologic criteria can reliably distinguish AMN-severe but fail to differentiate AMN-mild from AMN-moderate. AMN from atypical-mole syndrome cannot be diagnosed using pathologic criteria alone.

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.

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