Mitotic rate and S-phase fraction as prognostic factors in stage I cutaneous malignant melanoma

Clinical data from 369 patients with clinical stage I cutaneous malignant melanoma treated in Kuopio University Hospital district between 1974 and 1989 with a mean follow-up of 6.4 years were analysed. Clinical parameters, histology, DNA index, S-phase fraction (SPF) and mitotic indices [mitotic activity index (MAI) and volume-corrected mitotic index (M/V index)] were correlated with the outcome of the disease to establish their value as predictors of stage I cutaneous malignant melanoma. In univariate survival analyses, bleeding, gender, tumour thickness, level of invasion according to Clark, TNM category, MAI, M/V index and SPF were the most significant predictors of recurrence-free (RFS) and overall survival. In Cox's multivariate analysis, tumour thickness (P = 0.0021), bleeding (P = 0.0106) and M/V index (P = 0.0058) predicted poor RFS in the 259 patients available for the analysis. Poor overall survival was predicted by MAI (P = 0.0002), bleeding (P = 0.004), SPF (P = 0.009) and male gender (P = 0.034). The present results indicate that mitotic activity index (MAI), volume-corrected mitotic index (M/V index) and S-phase fraction (SPF) are important prognostic factors in addition to the well-established Breslow thickness in stage I cutaneous malignant melanoma.