Clinical Features of Nasal and Paranasal Mucosal Melanomas in the Era of Immune Checkpoint Inhibitors: Insights From a Single‐Institution Analysis

Immune checkpoint inhibitors (ICIs) have become the mainstay of systemic therapy for nasal cavity and paranasal sinus mucosal melanoma (NPMM), which can be classified into nasal cavity mucosal melanoma (NMM) and paranasal sinus mucosal melanoma (PMM). However, the clinical characteristics and prognostic factors of NPMM in the ICI era remain poorly defined, and real-world data are still limited. This study aimed to characterize the respective clinical features of NMM and PMM and to identify prognostic factors of NPMM in a real-world setting where ICIs are available. This retrospective study included 23 Japanese patients with NMM (n = 15) or PMM (n = 8) treated between 2015 and 2023. The diagnoses were confirmed clinically and histopathologically. Clinical data were evaluated using the Mann-Whitney U test, chi-square test, receiver operating characteristic curve analysis, and Kaplan-Meier survival analysis. Among 23 patients with NPMM, 22 patients (95.7%) received ICIs, with one patient declining ICI therapy. Compared with NMM, PMM patients showed significantly larger tumor size, more frequent bone invasion, shorter progression-free survival (PFS), as well as higher neutrophil counts and lower lymphocyte and platelet counts in the peripheral blood. Notably, neither neutrophil nor lymphocyte count alone correlated significantly with survival, but the neutrophil-lymphocyte ratio (NLR), which integrates both, was significantly higher in PMM and associated with worse prognosis at a cutoff of ≥ 4. Other poor prognostic factors included tumor size ≥ 45.5 mm, platelet count ≤ 247.5 × 103/μL, and paranasal sinus origin. This study suggests that PMM shows significantly different outcomes compared with NMM, and that an elevated NLR may serve as a practical prognostic biomarker in the era of ICIs.