MALIGNANT-MELANOMA IN THE CNS, SUBTYPING AND IMMUNOCYTOCHEMISTRY

Paraffin-embedded specimens from 21 patients (mean age 49 years) with malignant melanocytic tumors of the central nervous system were studie d. Extraneuronal primary tumors were situated at the trunk (38%), the lower (14%) or upper extremity (10%), and the head/neck region (5%). I n 33% no extraneural primary tumor could be detected. The tumor locati on was frontal (19%), occipital (19%), parietal, spinal, multifocally (14%, respectively), or temporal (5%). Four subtypes were distinguishe d according to the predominant histological cell type: pleomorphic, ep ithelioid, spindle-and mixed-cell tumors, 29% contained no melanin, mo st of them belonging to the epithelioid subtype. The morphology and im munohistochemical reactivity for different antibodies (KL-1, EMA, VIM, HMB-45, NKI-C3, S-100, and MIB-1/Ki-67) were assessed. Positive stain ing was demonstrated for HMB-45 (in 86% of cases), NKI-C3 (100%), S-10 0 (95%), vimentin (75%), and KL-1 (33%). No expression of the cytokera tin EMA could be detected, The mean proliferation index measured by MI B-1 immunoreactivity was 21%. The 4 histological subtypes were found t o express different antigen patterns. In the analysis of CNS tumors of unknown origin, the panel of antibodies used for diagnosis should inc lude HMB-45 as the most specific marker for malignant melanoma.