MIB-1 immunoreactivity correlates with metastatic dissemination in primary thick cutaneous melanoma

Background: The proliferation rate of transformed cells is a putative prognostic indicator. MlB-1 is a murine monoclonal antibody to a Ki-67 epitope that detects a nuclear antigen found only in proliferating cells. Objective: The aim of this study was to test for a correlation between MIB-1 immunoreactivity and the metastatic potential of malignant melanoma. Methods: MIB-1 reactivity (% total tumor nuclei) was assessed in 34 formalin-fu;ed, paraffin-embedded primary cutaneous melanomas and correlated with metastatic potential and overall survival (follow-up, 10.5 +/- 1.8 years). Results: Whereas no correlation was found between MIB-1 reactivity and metastases in primary thin cutaneous melanoma (Breslow thickness, <0.75 mm; mean thickness, 0.39 +/- 0.16 mm), good correlation was found (p=0.0001) in primary thick cutaneous melanoma (Breslow thickness, >1.5 mm; mean thickness, 3.0 +/- 1.3 mm). MIB-1 reactivity was 12.3% +/- 7.7% and 0.7% +/- 1.3% with and without metastases, respectively, and was highest in the primary melanomas that later metastasized. However, overall survival in patients with thick cutaneous melanoma and metastases did not correlate with MIB-1 reactivity. Conclusion: MIB-1 proliferative activity is a useful prognostic indicator in primary cutaneous melanomas thicker than 1.5 mm and may predict the development of metastases.