Prognostic factors in localized invasive primary cutaneous malignant melanoma: results of a large population-based study

Summary Background The prognostic impact of several histopathological prognostic features in cutaneous malignant melanoma (CMM) remains controversial. Objectives To assess the independent prognostic value of mitotic rate, regression, tumour-infiltrating lymphocytes (TILs) and growth phase in primary stage I and II CMMs. Methods Clinicohistopathological data were obtained from the Stockholm–Gotland registry for 4237 patients diagnosed with an incident primary stage I or II CMM followed up to December 2011. The risk of CMM-specific death was evaluated by a Cox regression model. Results A mitotic rate of 1–10 mitoses per mm2 [hazard ratio (HR) 1·69, 95% confidence interval (CI) 1·16–2·45] and > 10 mitoses per mm2 (HR 2·27, 95% CI 1·46–3·52) were significant; TILs and regression were not. A more detailed analysis of data assessed between 1989 and 1995 confirmed significantly increased HRs for the presence vs. absence of mitoses (HR1–5/mm² 2·25, 95% CI 1·36–3·76; HR6–10/mm² 2·34, 95% CI 1·23–4·44; HR> 10/mm² 2·64, 95% CI 1·39–4·99). Other prognosticators were increasing T-stage vs. T1, presence of ulceration and presence of vertical growth phase (VGP). In T1 CMMs, an increasing tumour thickness vs. 0·8 mm 2·92, 95% CI 1·57–5·43) and presence of ulceration were significantly associated with higher HRs; mitotic rate, TILs, regression and growth phase were not. Conclusions Determinants of increased risk of CMM death in stage I and II CMMs were increasing T-stage, presence of ulceration, presence of mitoses and VGP. This was not found for TILs or regression.