Synchronous primary cutaneous melanomas: a descriptive study of their clinical features, histology, genetic background of the patients and clinical outcomes.

BACKGROUND: Around 0.5% of cutaneous melanoma (CM) patients will present with synchronous melanomas when first seen. Moreover, 26-40% of patients with multiple primary melanomas present with synchronous lesions. OBJECTIVES: To assess the prevalence, clinical and histopathological characteristics, germline mutations and outcome in patients with synchronous melanoma. METHODS: Clinical and histopathological data from 4703 melanoma patients were included. Clinical, histological and genetic mutational status information was analysed. Kaplan-Meier curves were used to investigate survival outcomes. RESULTS: A total of 144 patients (3.06%) presented simultaneously with two or more primary melanomas. During follow-up, 25.7% of patients with synchronous melanoma developed a new primary melanoma compared to 8.6% of patients diagnosed with single melanoma (P < 0.001). Germinal CDKN2A mutations were identified in 10.7% of patients with synchronous melanomas and genetic variants in MC1R in 72%. No significant differences in all survival outcomes between patients with synchronous melanomas and single melanomas were found. CONCLUSION: Synchronous melanomas are more frequent than previously reported and are more frequent in older patients compared to single melanomas. Moreover, these patients have a higher risk of developing a new primary melanoma during follow-up and have higher rates of germline susceptibility variants. Nevertheless, these findings were not associated with worse outcomes.