MIB-1 monoclonal antibody to determine proliferative activity of Ki-67 antigen as an adjunct to the histopathologic differential diagnosis of Spitz nevi

Background: The histopathologic differential diagnosis of Spitz nevus (SN) from malignant melanoma (MM) may be difficult. Objective: Our purpose was to determine the staining pattern and usefulness of MIB-1 antibody, which recognizes Ki-67 antigen in formalin-fixed, paraffin-embedded tissue, as an adjunct to the histopathologic differential diagnosis of SN. Methods: Twenty-five compound SNs, 27 MMs, and 26 compound nondysplastic melanocytic nevi (MNs) were immunostained with the MIB-1 antibody. Results: The mean counts of MIB-1-stained tumor cells of the epiderm:ll and dermal components, both alone and together, were significantly lower in SNs and MNs than in MMs (P < .0001). The dermal counts showed the best discriminating power. In addition, the mean dermal/epidermal count ratios for MIB-1 in SNs and MNs (0.25 and 0.23, respectively) were significantly lower than the corresponding ratio (0.94) in MMs (P < .0001). Conclusion: MIB-1-stained tumor cell counts, especially of the dermal component, anti dermal/epidermal MIB-1 count ratios may be helpful as an adjunct to the histopathologic differential diagnosis of SN.