Proliferative activities in Spitz nevus compared with melanocytic nevus and malignant melanoma using expression of PCNA/cyclin and mitotic rate.

Proliferative activity in Spitz nevus (SN) was determined using proliferating cell nuclear antigen (PCNA) immunostaining and by assessing the mitotic rate. It was compared with that in compound melanocytic nevus (MN) and in malignant melanoma (MM). The PCNA index (number of positive cells/1,000 tumor cells) in SN was 72.8 +/- 45.5% (mean +/- SD), which was statistically significantly higher than that in MN (7.2 +/- 2.7%) and lower than that in MM (248.5 +/- 110%). The PCNA-positive cells in SN and MM were found both in dermal and junctional nests, while those in MN were found almost exclusively in the dermal nests. The mitotic rate in SN was 1.4 +/- 0.96%, while it was nothing in MN and 5.4 +/- 4.2% in MM. There was a statistically significant correlation between the PCNA index and the mitotic rate at r = 0.8946, p < 0.001. The PCNA index, however, appeared to show the proliferative activity of SN more clearly than did the mitotic rate.