Proliferative activity in Spitz's naevi compared with other melanocytic skin lesions

Proliferative activity has been shown to correlate with the degree of malignancy in various human neoplasms. Immunostaining with the monoclonal antibody PC10 binding to proliferating cell nuclear antigen (PCNA) facilitates the assessment of proliferation in routinely fixed, paraffin-embedded tissue sections. In this study we investigated the expression of PCNA in 29 Spitz's naevi in comparison with 43 primary malignant melanomas (MM), 18 cutaneous metastases of malignant melanoma (MMM) and 16 benign melanocytic naevi (BMN). After selection of the microscopic field with the highest number of PCNA-positive nuclei, the nuclear density (NDmax) of PCNA-stained nuclei in this field was assessed using interactive image analysis. The mean value of NDmax (given as 1000 nuclei/mm3 tissue) of SN was 27.9 (+/- 16.7) and differed significantly from that of MM (48.1 +/- 40.5; U-test: p < 0.05) and that of MMM (114.4 +/- 56.3; p < 0.01). Comparing NDmax of the subgroups of MM according to their maximal vertical tumour thickness with NDmax of SN we found significant differences only between SN and MM > 1.5 mm thick (n = 14; NDmax = 67.8 +/- 36.1) but not between SN and MM < or = 1.5 mm thick (n = 29; NDmax = 38.8 +/- 39.3). PCNA expression in SN did not differ from that of BMN (NDmax 23.8 +/- 28.5). Proliferative activity as assessed by measurement of PCNA expression therefore showed significant differences between BMN, SN and thin primary melanomas on one hand and thick primary melanomas and cutaneous metastases of malignant melanomas on the other hand.