Absolute Risk of Developing a Second Primary Cancer After a First Primary Melanoma: An Australian Population-Based Cohort Study.

Understanding the absolute risk of developing a second primary cancer is important to guide patient surveillance and education. We aimed to examine the cumulative incidence and factors associated with development of a second primary cancer (melanoma versus other) after diagnosis of a first primary melanoma (invasive or in situ). We analysed a population-based study cohort of 154,695 people diagnosed with a first primary melanoma in New South Wales, Australia, between 1982-2019. The cohort was followed for future cancer incidence and vital status for a median of 7.0 years. We used Fine-Gray models to account for death as a competing risk. After a first primary melanoma, 23.7% developed a second primary cancer, including 12.7% who developed a second primary invasive or in situ melanoma (mean 5-year risk: 7.6%). The next most common second primary cancer types were prostate, breast and colon cancers, with mean 5-year risks after the initial melanoma diagnosis of 2.8% (male-specific incidence), 0.7% (2.8% female-specific incidence), and 0.6%, respectively. The most common second primary cancer among people with a first primary melanoma was another melanoma (invasive or in situ), requiring long-term careful surveillance of their skin even if the probability of recurrence from the first melanoma is low.