Survival and prognostic factors of salivary gland malignant mixed tumor-not otherwise specified: A population-based analysis.

Objective: Malignant mixed tumors of the salivary gland are a group of neoplasms comprised of carcinoma-ex-pleomorphic adenoma, carcinosarcoma, and metastasizing pleomorphic adenoma. An alternative classification, malignant mixed tumor-not otherwise (MMT-NOS), is a diagnosis of exclusion for neoplasms that do not fit the previous histologically profiled subtypes. The objective was to provide a comprehensive assessment of MMT-NOS and determine prognostic factors.

Methods: This retrospective cohort study queried the Surveillance, Epidemiology, and End Results database for patient and tumor characteristics of US patients with MMT-NOS of the major salivary glands from 1973 to 2016. Kaplan-Meier and Cox regression analysis were performed to determine 5-year survival and prognostic factors.

Results: 434 patients were identified with a mean age at diagnosis of 61.5 years. The majority of neoplasms were high grade and stage (70.8% grade III/IV; 63.8% stage III/IV). Extraparenchymal extension (40.6%) and lymph node involvement (28.5%) were common; distant metastases (2.4%) were rare. Treatment included surgery (93.0%), radiation (51.6%), and chemotherapy (10.4%). Facial nerve sacrifice was common (50.8%). Median survival was 66.5 months. 5-year overall and disease-specific survival were 65.7% and 83.0%, respectively. In multivariate analysis, nodal involvement (HR 7.0; P < 0.001), surgery-radiation-chemotherapy (HR 6.1; P = 0.02), extraparenchymal extension (HR 2.50; P = 0.04), and tumor size >4 cm (HR 1.3; P = 0.03) were prognostic factors.

Conclusion: Despite high stage and grade at diagnosis, MMT-NOS portends a good 5-year prognosis and low rate of distant metastasis. Prognostic factors were nodal involvement, tumor size, and extraparenchymal extension.