The Ki-67 antigen in primary human melanomas ?its relationship to mitotic rate and tumor thickness and its stability

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Abstract
We investigated whether two parameters of proliferative activity — mitotic rate and Ki-67 positive cells — are interchangeable. The mitotic rate was assessed on paraffin-embedded sections, Ki-67 positive cells were immunohistologically determined in frozen tissue. A poor correlation (correlation coefficient r=0.57) was found between both parameters. The proliferative activity was often not homogeneously distributed in the tested tumors. However, this is a major reason for the observed difference only in thin melanomas (<1.5 mm) as seen by comparison of tumors with homogeneous and inhomogeneous proliferative activity. We assume that arrest of cells in different stages of the cell cycle — variable from melanoma to melanoma — is the major reason for the observed discrepancy between mitotic rate and Ki-67 positive cells in tumors of 1.5 mm and thicker. The mean number of Ki-67 positive cells increased with tumor thickness. The stability of the Ki-67 antigen towards freezing, thawing, and formalin was studied.