Characteristics of spitzoid melanoma and clues for differential diagnosis with spitz nevus.

The different features of spitzoid melanoma are not well characterized in the literature, and the lesion often has to be described in comparison with Spitz nevus. We evaluated the histopathological appearance of spitzoid melanoma by reviewing all spitzoid melanomas treated at our hospital and all referrals from 1998 to 2010. The final study sample comprised 18 cases, 11 from our institution and 7 referrals from other centers. We recorded clinical parameters (eg, age, sex, site, time between onset and excision, recurrence, and death) and a series of histopathological parameters (eg, size, ulceration, symmetry, Clark level, Breslow thickness, cell density, atypia, mitosis). Clinical and histopathological criteria were not available for the 7 referrals. Mean age was 35.2 years (15-56), and 8 patients were women. Mean size of the lesions was 7.27 mm (Clark III/IV and Breslow 2.51 mm), and these were found on the limbs and trunk. Cell density was high in 10 cases and atypia present in 9 (marked in 1). Mitoses were observed in 8 cases (atypical in 4, clusters in 4). Maturation was absent in 9 cases and zonation in 8. Our analysis revealed 5 previously undefined subtypes of spitzoid melanoma (genuine (7 cases), uniform (5 cases), packed (5 cases), polypoid (3 cases) and pigmented (2 cases)]. Four cases showed 2 patterns at the same time. The most useful parameters for the differential diagnosis were cell density, mitosis, zonation, infiltration pattern, and consumption of the epidermis. Assignation of a spitzoid melanoma to 1 of more of our 5 subtypes can enable a more confident diagnosis to be made.