Prognostic subclassifications of T1 cutaneous melanomas based on ulceration, tumour thickness and Clark's level of invasion: results of a population-based study from the Swedish Melanoma Register.

BACKGROUND: Survival and prognostic factors for thin melanomas have been studied relatively little in population-based settings. This patient group accounts for the majority of melanomas diagnosed in western countries today, and better prognostic information is needed.

OBJECTIVES: The aim of this study was to use established prognostic factors such as ulceration, tumour thickness and Clark's level of invasion for risk stratification of T1 cutaneous melanoma.

METHODS: From 1990 to 2008, the Swedish Melanoma Register included 97% of all melanomas diagnosed in Sweden. Altogether, 13,026 patients with T1 melanomas in clinical stage I were used for estimating melanoma-specific 10- and 15-year mortality rates. The Cox regression model was used for further survival analysis on 11,165 patients with complete data.

RESULTS: Ulceration, tumour thickness and Clark's level of invasion all showed significant, independent, long-term prognostic information. By combining these factors the patients could be subdivided into three risk groups: a low-risk group (67·9% of T1 cases) with a 10-year melanoma-specific mortality rate of 1·5% (1·2-1·9%); an intermediate-risk group (28·6% of T1 cases) with a 10-year mortality rate of 6·1% (5·0-7·3%); and a high-risk group (3·5% of T1 cases) with a 10-year mortality rate of 15·6% (11·2-21·4%). The high- and intermediate-risk groups accounted for 66% of melanoma deaths within T1.

CONCLUSIONS: Using a population-based melanoma register, and combining ulceration, tumour thickness and Clark's level of invasion, three distinct prognostic subgroups were identified.