[476] Clinicopathologic, Immunohistochemical and Molecular Analysis in the Differential Diagnosis of Reed Nevus and Spindle Cell Melanoma.

Alba Diaz, Sofia Hakim, Alexandra Valera, Adriana Garcia, Cristina Carrera, Josep Palou, Susana Puig, Josep Malvehy, Llucia Alos. Hospital Clínic, University of Barcelona, Spain

Background: Reed nevus or pigmented spindle cell nevus, a variant of Spitz nevus, is a distinctive benign acquired lesion which mimics melanoma clinically and histologically. The main goal was to study a series of Reed nevi and spindle cell melanomas in order to elucidate useful features in their differential diagnosis.
Design: We collected 34 tumors, including 18 Reed nevi and 16 spindle cell melanomas. Clinical and histopathological features were reviewed. Using tissue microarrays, immunostains for HMB45, Ki67, cyclin D1, p53, p27KIP1 and p16INK4 were performed. In 21 cases (11 Reed nevi and 10 melanomas) we carried out fluorescence in situ hybridization (FISH) using probes targeting RREB1 (6p25), MYB (6q23), CEP6 (centromere 6) and CCND1 (11q13)(Abbott).
Results: In comparison with spindle cell melanomas (13 superficial spreading melanomas and 3 lentigo maligna type), Reed nevi presented in younger patients (mean 27 vs 61 years old, p<0.001), affected more frequently women (88% vs 50%, p=0.017) and predominantly presented in lower extremities while melanomas did in trunk and face. Reed nevi showed a smaller size (mean 3.6 vs 7.6 mm, p<0.001). Histological characteristics favouring the diagnosis of Reed nevus were: nests uniformity (p<0.001), symmetry (p<0.001), well-defined lateral demarcation (p=0.002), epidermal hyperplasia (p=0.005) and dermal melanophagia (p=0.002). Those favouring the diagnosis of melanoma were: lentiginous pattern (p=0.012), cytological atypia (p<0.001), high mitotic count (p<0.001), dermal regression (p<0.001) and elastosis (p<0.001). Conversely, we did not find significant differences in pagetoid or adnexal spread of tumor. Ki67 index was higher in melanomas than in Reed nevi (mean 11 vs 2%, p=0.009), whereas the rest of markers did not show significant differences. Five out of 11 Reed nevi (45%) were positive by FISH although they only met one criterion (gains in RREB1 greater than 29% of cells, but never higher than 40%). Conversely, all melanomas showed chromosomal alterations, most of them meeting 2 or more criteria.
Conclusions: Recently, ancillary techniques such as FISH have been developed in order to assist in the diagnosis of melanocytic lesions. However they must be assessed together with clinical and histological characteristics which are still essential for the differential diagnosis between Reed nevus and melanoma.
Category: Dermatopathology

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 115, Tuesday Morning


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