Mast cells in melanocytic skin lesions. An immunohistochemical and quantitative study.

The mast cells participate in inflammation and possibly in carcinogenesis. The aim of the study was to study mast cells in melanocytic lesions. The material consisted of 24 pigmented nevi, 18 dysplastic nevi and 19 melanomas. The sections were stained immunohistochemically for tryptase and chymase. Positive cells were counted inside the lesions and at the interface between the lesion and dermis. The mean intralesional tryptase+ count was 15.75 for nevi, 21.78 for dysplastic nevi, and 8.07 for melanomas. The chymase+ intralesional count was 14.89 for nevi, 21.88 for dysplastic nevi, and 11.34 for melanomas. The tryptase+ perilesional count was 16.89 for nevi, 15.93 for dysplastic nevi, and 15.71 for melanomas. The chymase+ perilesional count was 16.52 for nevi, 16.16 for dysplastic nevi, and 14.77 for melanomas. The tryptase/chymase intralesional ratio was 0.93 for nevi, 1.05 for dysplastic nevi, and 1.67 for melanomas. The tryptase/chymase perilesional ratio was 1.02 for nevi, 1.09 for dysplastic nevi, and 1.00 for melanomas. The differences between intralesional mast cells, both tryptase+ and chymase+, were statistically significant. The intralesional tryptase+ count showed an inverse correlation to age (R = -0.42); this correlation was the strongest in melanomas. The results obtained in our study suggest a possible correlation between mast cells and the pathogenesis of cutaneous melanoma.