Immunohistochemical evaluation of necrotic malignant melanomas.

We evaluated 35 cases of malignant melanomas with substantial necrosis immunostained with S-100, HMB-45, Melan-A, tyrosinase, PNL2, and microphthalmia transcription factor (MITF). Staining patterns were evaluated in viable and necrotic areas of the tumors. S-100 was the most sensitive marker (97%) in the viable tumors, but necrotic areas demonstrated nonspecific staining. Viable tumors stained variably for HMB-45 (25 [71%]), Melan-A (28 [80%]), tyrosinase (30 [86%]), and PNL2 (23 [66%]). Necrotic areas focally reacted to the same antibodies. The necrotic areas that retained immunoreactivity for these markers corresponded to areas where the outline of the tumor cells could still be recognized as ghost cells on the H&E-stained section. Areas that showed complete coagulative necrosis were negative for melanoma markers. MITF variably stained in the viable tumors but was completely negative in necrotic areas. Our study demonstrated that a combination of antibodies to HMB-45, tyrosinase, and PNL2 detected melanocytic differentiation in necrotic areas in 80% of cases.