Incidence and Factors Associated With Second Primary Invasive Melanoma in Norway

Importance Patients diagnosed with a primary melanoma are at high risk of subsequent melanomas. Understanding the risk of second primary invasive melanoma and associated factors is crucial to optimize patient follow-up. Objective To assess the incidence rate of second primary invasive melanoma and time between the first and second primary invasive melanoma in the Norwegian population. Design, Setting, and Participants This population-based cohort study included data from deidentified records of all invasive melanomas diagnosed in Norway in 2008 to 2020, obtained from the Cancer Registry of Norway. Data were from adults aged 18 years or older diagnosed with a first primary melanoma. Data analysis was performed from March to August 2023. Main Outcomes and Measures The main outcome was the incidence rate of second primary invasive melanoma at least 30 days after the first. Accelerated failure time models were fitted to examine potential associations with patient and tumor characteristics. Median time between first and second primary melanomas and 95% CIs were calculated. The likelihood of, and median interval for, second primary melanomas on the same or different site as the first primary were calculated. Results A total of 19 196 individuals aged 18 years or older were diagnosed with a first primary melanoma. The mean (SD) age at diagnosis of the first primary melanoma was 62 (16) years (range, 18-104 years), and 9763 (51%) were female. The incidence rate in the year following diagnosis was 16.8 (95% CI, 14.9-18.7) per 1000 person-years, which decreased to 7.3 (95% CI, 6.0-8.6) during the second year and stabilized thereafter. Median time between first and second primaries decreased with advancing age and was 37 months (95% CI, 8-49) in patients younger than 40 years, 18 (95% CI, 13-24) in patients aged 50 to 59 years, and 11 (95% CI, 7-18) in patients aged 80 years or older. The second primary was on the same site as their first primary for 47% (359 patients), and on a different site for 53% (407 patients). The median interval until second melanoma on the same site as the initial melanoma was 12 (95% CI, 7-19) months in men and 22 (95% CI, 11-35) months in women. Conclusions and Relevance Older age and male sex were associated with an increased risk, suggesting that increased surveillance intensity may be considered for men, especially those older than 50 years, for at least 3 years after their initial diagnosis, regardless of the characteristics of their first invasive melanoma.