Abstract
IMPORTANCE: Melanoma is one of the most rapidly increasing forms of cancer worldwide. Most studies about survival among patients with melanoma consider only the primary tumor and disregard the potential effect of multiple primary tumors. A better understanding of the prognosis of patients with multiple primary melanoma is important for patient counselling and follow-up strategies. OBJECTIVE: To describe the epidemiologic features of multiple primary melanoma in patients from the Netherlands. DESIGN, SETTING, AND PARTICIPANTS: This retrospective, population-based cohort study included adults with histologically proven, primary, invasive cutaneous melanoma in the Netherlands between January 1, 2000, and December 31, 2014, with a median follow-up of 75.1 months, using data from PALGA, the Dutch Nationwide Network and Registry of Histopathology and Cytopathology. Follow-up data were retrieved from the Netherlands Cancer Registry. Statistical analysis was performed from August 1, 2018, to September 3, 2018. MAIN OUTCOMES AND MEASURES: A multivariable Cox model with a time-varying covariate was performed to assess overall survival between patients with a single primary melanoma vs those with multiple primary melanomas. Secondary outcomes included incidence of multiple primary melanoma, differences in Breslow thickness, and time between first and second multiple primary melanoma. RESULTS: Of the 56 929 study patients, 31 916 (56.1%) were female, with a mean (SD) age of 56.4 (16.2) years. A total of 54 645 single primary melanomas and 4967 multiple primary melanomas in 2284 patients were included. The median Breslow thickness decreased from 0.90 mm (interquartile range, 0.55-1.70 mm) for the first melanoma to 0.65 mm (interquartile range, 0.45-1.10 mm) for the second melanoma (P < .001). For their second melanoma, 370 patients (16.2%) had a higher T stage, 1112 (48.7%) had the same T stage, and 802 (35.1%) had a lower T stage. In addition, 841 of 2284 second melanomas (36.8%) in patients with multiple primary melanomas were found during the first year of follow-up, whereas 624 of 2284 (27.3%) were found after 5 years of follow-up. These proportions did not vary when stratified for melanoma stage. Worse overall survival was seen among patients with multiple primary melanomas compared with patients with a single primary melanoma (hazard ratio, 1.31; 95% CI, 1.20-1.42; P < .001). CONCLUSIONS AND RELEVANCE: A significant decrease in Breslow thickness between the first and second multiple primary melanoma was found, and overall survival among patients with multiple primary melanomas was significantly worse than that among patients with a single primary melanoma. These findings suggest that more strict follow-up strategies may be warranted for patients with multiple primary melanomas.