Who Will Have a Second Melanoma? A Prospective Longitudinal Study in Patients without Any Genetic Predisposition.

Background: Melanoma patients have a higher risk of developing additional melanomas. Predisposing factors of a second primary melanoma in patients without any genetic predisposition are not well established.

Objectives: The aim of this study was to identify risk factors related to the development of a second primary melanoma in order to know which patients should be followed up closely.

Methods: A longitudinal study was performed at Hospital Gregorio Marañón (Madrid, Spain), based on follow-up data of patients diagnosed with cutaneous melanoma from 1998 to 2020.

Results: After a median follow-up of 82 months, 58 out of 1523 (3.8%) patients developed a second melanoma. In 11 patients (19%), a second melanoma was diagnosed more than 10 years after their first melanoma. Second melanomas more commonly had a lower mean tumour thickness than the first ones, but 8 out of 58 (13.8%) had a higher tumour thickness than their first melanoma. Skin phototype I-II, having more than 50 melanocytic nevi, and recurrent sunburns were associated with the development of a second melanoma. In multivariate analysis, skin phototype I-II (odds ratio [OR] = 5.41; p < 0.001) and a higher number of nevi (OR = 3.44; p < 0.001) remained as independent risk factors for the development of a second melanoma.

Conclusions: Patients with fair skin phototype and more than 50 melanocytic nevi are at increased risk of developing a second primary melanoma and should be closely monitored throughout their lives to detect earlier additional melanomas.