Long-term survival of melanoma patients according to primary tumour thickness – an Australian population-based study

Background: For most patients with newly-diagnosed melanomas their disease is localised (AJCC Stage-I and II) and they can be given an estimate of their risk of dying of melanoma based on the Breslow thickness of the primary tumour provided in the pathology report. This study sought to investigate the impact of T category on long-term survival by examining its effect on the incidence of both melanoma-related and non-melanoma-related death in a large population-based dataset. Methods: Data were analysed for 210,042 patients diagnosed with invasive cutaneous melanoma (from 1982-2014). The information was obtained from all eight Australian state and territory cancer registries, to which reporting of every cancer diagnosis is mandatory, and from the National Death Index. Melanoma-specific survival (MSS) and overall survival (OS) stratified by T category were determined using the Kaplan-Meier method and the rates at 10, 20 and 30 years were calculated. Proportional hazard models were used to quantify the relative risk differences between T categories adjusted for age, sex and body site. For each T category and at each follow-up time point, the rates of deaths due to melanoma and non-melanoma causes were determined using the cumulative incidence functions. Results: The MSS and OS rates for each T category at follow-up times of 10, 20 and 30 years are shown in Figures 1 and 2. Patients with a T1 melanoma (Breslow thickness ≤1.0mm) by 10 years post-diagnosis had a risk of dying from their melanoma of 4.1% and a risk of dying from a non-melanoma cause of 11.8%; after 30 years their risk of death due to melanoma was 7.1% and their risk of death from another cause 32.8%. For T2 melanomas (1.1-2mm in thickness) the risks of melanoma death and non-melanoma death after 10 years were 15.8% and 15%, respectively, for T3 melanomas (2.1-4mm) 29.0% and 21.8%, and for T4 melanomas (>4mm) 41.0% and 26.2%. Cumulative incidence of melanoma deaths over time following primary melanoma diagnosis. Cumulative incidence of non-melanoma deaths over time following primary melanoma diagnosis. Conclusions: This analysis of population-based Australian data provides reliable estimates of 10, 20 and 30-year risks of death due to melanoma and other causes according to thickness categories, which will be useful to both clinicians and patients.