PCNA expression and nucleolar organizer regions in malignant melanoma and nevus cell nevus.

The histogenesis of malignant melanoma with particular reference to the role of melanocytic nevus is still controversial in oncological pathology. In order to differentiate between the proliferative activity of malignant melanomas and benign melanocytic tumors, immunohistochemical analysis was carried out. We used monoclonal antibody PC10 to identify the Proliferating Cell Nuclear Antigen (PCNA), a highly conserved 36 KD acidic nuclear protein which correlates with cell proliferation, and the AgNOR method to stain the Nucleolar Organizer Regions (NORs) whose number and configurations may reflect protein synthesis activity. 47 cases of primary melanoma, 63 metastatic melanoma lesions, and 23 cases of nevi are included in this study. Spitz nevi showed a higher index of cell proliferation compared with other common benign nevi but a much lower index compared with malignant melanoma cells. The metastatic lesions of malignant melanomas had a higher index of proliferation and activity of cells than the primary lesions. Skin-metastatic lesions had higher indexes of cell proliferation and NOR activity than lymph node-metastatic lesions. These results support the idea that metastatic melanoma cells are derived from a more advanced stage of tumor progression. These data suggest that the combination of PCNA and AgNOR is an useful marker for differentiating benign melanocytic tumors from malignant melanomas.