Synchronous Melanoma: Definition, Prognosis, and Implications. A Comprehensive Review of Literature

BACKGROUND: Although multiple primary melanomas (MPMs) have been reported in the literature, the subgroup of synchronous melanomas (SMs) remains understudied. METHODS: We conducted a comprehensive systematic review of the English literature from 1972 to 2023 to characterize SM. Our objective was to clarify the definition, determine incidence and prognosis, and present recommendations. RESULTS: We found 18 case series articles and six case reports that met our criteria. Twelve of eighteen studies defined SM as a second primary melanoma identified within 1 month. The total number of SM patients reported was 1083. The cumulative percentage of MPM in total melanoma patients was 2.9 %, and the cumulative percentage of SM patients in MPM patients was 31.3%. SM patients trended toward higher body anatomical concordance, older age, and male sex. Despite limited data, SMs do not show a worse prognosis for patients compared with single melanomas. CONCLUSIONS: Despite a lack of consensus in the past, we recommend that SM be defined as a second primary melanoma detected within 1 month of the initial diagnosis. SMs comprise almost one-third of MPM cases and do not seem to carry any worse prognosis than the patients presenting with single melanoma. We believe older age and male sex may be more prone to SM. We recommend patient education, self-skin evaluations and TSE at initial and follow-up visits. Neither randomized controlled trials nor meta-analyses on SM exist. Ideally, further studies with a large cohort of patients are needed to accurately define SM.