Mitotic indices, anti-PCNA immunostaining, and AgNORs in thick cutaneous melanomas displaying paradoxical behaviour

Those melanomas which fail to behave as expected from their Breslow thickness provide interesting material for study. In an attempt to explain differences in behaviour, we have evaluated three distinct proliferative markers in 23 thick melanomas which failed to metastasize and in 20 well-matched control tumours with documented metastasis. The test group demonstrated significantly greater numbers of mitoses when expressed as an index (mitoses per 1000 cells), whilst no difference was found when the results were expressed in terms of mitoses per unit area. Tumours showing epidermal ulceration possessed higher mitotic indices than those of non-ulcerated lesions. High fractions of PCNA immunolabelling combined with low mitotic indices were observed frequently in the non-metastasizing group. This result and its possible relation to survival advantage are discussed in detail. Both AgNOR numbers and patterns failed to act as prognostic variables--indeed, AgNORs failed to correlate with the other proliferative indices, suggesting that their value as a marker of tumour growth is severely limited.