The superficial atypical Spitz tumor and malignant melanoma of superficial spreading type arising in association with the superficial atypical Spitz tumor: A distinct form of dysplastic Spitzoid nevomelanocytic proliferation.

Spitzoid lesions are diagnostically problematic because of a deceptive morphology and indeterminate behavior. The most problematic are atypical Spitz tumors whereby distinction from melanoma may be difficult. We have recognized a melanocytic lesion with a reproducible histomorphology, demonstrating characteristic demographic features, namely a predilection to involve younger female patients and common occurrence on the thigh. We have designated this lesion as the superficial atypical Spitz tumor and have encountered 27 cases. We believe that these lesions overlap histomorphologically with higher-grade dysplastic nevi and de novo intraepidermal epithelioid melanocytic dysplasia. We identified 19 additional cases that appear to represent transition into malignant melanoma of superficial spreading type arising in a background of the superficial atypical Spitz tumor. A limitation is that complete medical histories were not obtained for all patients. In conclusion, there exists a distinct subset of Spitz tumors that we designate as the superficial atypical Spitz tumor in which there is inherent dysplasia including lesions that evolve into melanoma of superficial spreading type.