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

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 (less than 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.