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.