Proliferation indices correlate with diagnosis and metastasis in diagnostically challenging melanocytic tumors

The diagnosis of melanocytic lesions remains a formidable challenge in dermatopathology. For diagnostically challenging lesions, ancillary tests are available to inform the diagnosis, including immunohistochemistry and molecular testing (particularly fluorescence in situ hybridization [FISH]). However, the test result that most robustly informs the diagnosis remains controversial. Thirty-seven diagnostically challenging melanocytic lesions from our consultation service were reviewed. Histopathologic, immunohistochemical, and second-generation FISH results (NeoGenomics; probes 6p25, 8q24, 11q13, 9p21, and centromere 9) were correlated with the final consensus diagnosis and clinical follow-up using logistic regression and Fisher exact test. Based on histopathologic and immunohistochemical features, cases were designated as "favor benign" (n = 19) or "favor malignant" (n = 18) by a consensus group of up to 7 dermatopathologists. The sensitivity of FISH for the diagnosis of melanoma was 39%, and the specificity was 84%. Univariate logistic regression models for a final diagnosis of melanoma showed that only increased Ki-67 positive dermal tumor cells (>= 5%; P = .01) significantly correlated with the diagnosis of melanoma. FISH result did not correlate with the final diagnosis (melanoma or nevus; P = .26). Follow-up (range, 8-29 months) was available for 35 cases (19 diagnosed as nevus and 16 as melanoma), and metastases (restricted to sentinel lymph nodes) were detected from 5 melanomas (3 FISH negative and 2 FISH positive). Only increased dermal mitotic figures (>1/mm(2)) correlated with metastases to sentinel lymph nodes (P = .04). Thus, in the classification of diagnostically challenging melanocytic lesions, indices of proliferation emerge as the most informative diagnostic adjuncts correlating with diagnosis and clinical behavior, respectively. (C) 2016 Elsevier Inc. All rights reserved.