Nevoid melanoma may be confused both clinically and histologically with benign nevi.

The aim of this study was to characterize the histologic features of nevoid melanoma.

Forty-three cases of nevoid melanoma from our laboratory were evaluated.

Our study cases included 33 men and 10 women with mean age of 62 years. The back was the most common site followed by the arm. A clinical diagnosis other than melanoma was made in about 40% of the cases. Two architectural patterns were identified: Plaque and polypoid. Sheetlike confluence of melanocytes expanding the papillary dermis was seen in 60% of the cases. Nests disposed in parallel arrays at the base of the tumor (parallel theque pattern) were present in roughly 81% of our series. Mitoses were evident in one-third of cases ranging from less than 1 to 4 per square millimeter.

Genomic abnormalities characteristic of melanoma were detected in 7 of 8 tested cases.

This is a descriptive study. No follow-up information was available for 32 of the 43 patients. In the other 11, follow-up was limited to the re-excision specimens.

Characteristic growth patterns including confluence of dermal melanocytes with no intervening connective tissue and the parallel theque pattern can be helpful in suggesting a diagnosis of nevoid melanoma at scanning magnification.