Histologic features of melanocytic nevi seen in association with mycosis fungoides.

BACKGROUND

Many different tumors have been reported to occur simultaneously as collision lesions. To date, no such events have been reported between mycosis fungoides (MFs) and melanocytic neoplasms.

METHODS

Two cases are presented in which patches of MF were superimposed on melanocytic nevi. In addition, 967 biopsies of MF from 411 patients were identified in an 8-year retrospective database search. Patient pathology history summaries were reviewed to identify inflamed nevi, atypical nevi, and melanoma submitted for histologic evaluation from this population.

RESULTS

The occurrence of MF in a congenital nevus was associated with a halo phenomenon restricted to the affected region of the nevus in one patient. In the other patient, nests of two morphologies (lymphocytic and melanocytic) in the same biopsy presented a potentially confusing histologic picture. No other cases of MF superimposed on a nevus were identified in 967 biopsies from 411 patients with a histological diagnosis of MF seen over the past 8 years. In this population, 57 biopsies of melanocytic lesions were identified from 28 patients, including three atypical nevi and three melanomas.

CONCLUSIONS

The presence of MF superimposed on a nevus is rare and may lead to confounding histologic features or the development of a halo nevus phenomenon.