A zonal comparison of MIB1-Ki67 immunoreactivity in benign and malignant melanocytic lesions

Differentiation between malignant melanomas and benign nevi can sometimes b e difficult by conventional histopathology, and additional diagnostic marke rs may be helpful. This study investigated the immunoreactivity of the cell proliferation marker MIB1-Ki67 in 23 compound nevi, 17 dysplastic nevi, 8 Spitz nevi (SN), and 24 malignant melanomas (MMs) and evaluated its ability in separating benign nevi from MMs. In each lesion, the average number (pe rcentage) of MIB1-positive nuclei (%MIB1-Mean) and the maximal number (perc entage) of MIB1-positive nuclei (%MIB1-Max) were determined from each of th e superficial, middle, and deep dermal zones of the lesion as well as from the entire lesion. The %MIB1-Max was determined from subjectively selected area(s) of high count. Malignant melanomas had a significantly greater %MIB 1-Mean and %MIB1-Max than all benign nevi in all individual zones and in th e entire lesion (p < 0.05). Discriminant analysis showed that the %MIB1-Mea n and %MIB1-Max counted from the whole lesions had better discriminating ab ilities than from the individual zones. By using the %MIB1-Mean from all zo nes, all lesions except 1 SN and 3 MMs could be correctly classified as ben ign or malignant. When using the %MIB1-Max from all zones, all but 2 SN cou ld be correctly separated as benign or malignant. Thus, MIB1-Ki67 immunorea ctivity closely correlates with the benignancy or malignancy of melanocytic lesions and may assist in the differentiation of benign nevi from MMs.