PRAME Staining in Sinonasal Mucosal Melanoma: A Single-Center Experience

Background Sinonasal mucosal melanoma (MM) is a rare, aggressive melanoma subtype. Complete surgical excision, with or without adjuvant radiotherapy, remains the cornerstone of treatment and yields adequate locoregional control. Metastatic MM is managed similarly to metastatic cutaneous melanoma but with poorer survival. PReferentially expressed Antigen in MElanoma (PRAME) has been identified as a potential diagnostic marker and therapeutic target in the treatment of cutaneous melanoma. Methods Retrospective analysis of the clinical characteristics and immunohistochemical features of all sinonasal MM patients referred to the department of Head and Neck Surgical Oncology, UMC Utrecht Cancer Center, between 2011 and 2021 was performed. Single nucleotide polymorphism (SNP) array and next-generation sequencing (NGS) were performed in selected cases. Results A total of 26 patients with an MM were included. The median follow-up duration was 15 months. At the end of follow-up, 13 patients had died due to progression of their disease, and one patient died of intercurrent disease. PRAME immunohistochemistry was performed in 23 out of 26 cases, all displaying PRAME expression. In two cases PRAME expression was present both within the melanoma cells and in melanocytes in adjacent mucosa. SNP array showed ≥ 5 copy number variants (CNV) in all tested cases, with a median of 29.5 CNVs (IQR 23.25–40). The three most common mutations identified by NGS were NRAS (7 cases) and NF1 (2 cases). Conclusion We show that expression of PRAME is common in sinonasal MM, making PRAME a useful ancillary diagnostic tool and a potential therapeutic target in sinonasal MM. The demonstrated occurrence of extensive presence of PRAME-positive melanocytes in the surrounding mucosa of sinonasal MM might explain the multifocal nature of melanoma in the (sinonasal) mucosa, and would be an extra argument for a PRAME targeting treatment in preventing local disease recurrence.