Nevoid melanoma: A study of 43 cases with emphasis on growth pattern

Abstract

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

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

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

Results: 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.

Limitation: 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.

Conclusion: 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.

Keywords: malignancy; melanocytic; melanoma; nevoid; parallel theque; skin; tumor.