Clinicopathologic characteristics and prognostic factors of mucoepidermoid carcinoma: a 20-year real-world cohort study.

BACKGROUND: The purpose of this study was to characterize the clinicopathologic features, treatment patterns, long-term outcomes, and prognostic factors of mucoepidermoid carcinoma (MEC) in a real-world cohort. MATERIALS AND METHODS: We retrospectively analyzed 283 patients with MEC treated between 2005 and 2025. Treatment included surgery, radiotherapy, and chemotherapy according to institutional protocols. Disease-free survival (DFS) and overall survival (OS) were estimated using the Kaplan-Meier method. Independent prognostic factors were evaluated using Cox proportional hazards models. RESULTS: With a median follow-up of 53 months (range 1-246), histological grading was available for 202 patients: 35.6% low-grade, 46.0% intermediate-grade, and 18.3% high-grade. The parotid gland (42.8%) and lung (19.4%) were the most common primary sites. Among 118 patients tested for cAMP response element-binding protein-regulated transcription coactivator 1/3-mastermind-like protein 2 (CRTC1/3-MAML2) fusion, 95 (80.5%) were fusion-positive, and fusion status was significantly associated with histological grade. Five-year DFS/OS rates were 100%/100% for low-grade, 88.2%/93.5% for intermediate-grade, and 70.7%/79.8% for high-grade tumors. High-grade tumors had significantly poorer survival than low- or intermediate-grade tumors, whereas low- and intermediate-grade tumors did not differ significantly, including after propensity score matching. Perineural invasion independently predicted DFS, whereas age, N classification, and primary site independently predicted OS. CONCLUSIONS: MEC showed marked prognostic heterogeneity by histological grade and primary site. Intermediate-grade MEC showed relatively favorable outcomes, but matched analyses were limited by small sample size and few events. CRTC1/3-MAML2 fusion was associated with histological grade, whereas its prognostic value remains exploratory.