Objectives: Given limited data availability on distant metastasis (DM) in major salivary gland (MSG) malignancy presentation, we aimed to evaluate the rate, histologic patterns, location, and predictors of DM at first MSG cancer presentation and suggest potential implications on diagnostic workup.
Study design: Retrospective cohort.
Setting: Commission on Cancer-accredited hospitals.
Methods: We included patients in the National Cancer Database (2010-2016) with MSG malignancy. Site and rate of DM were stratified by histologic subtype. Factors predictive of DM at presentation were determined by multivariate regression analysis. Survival analyses were conducted via the Kaplan-Meier method, log-rank test, and Cox regression analysis.
Results: Of 5776 patients with MSG carcinoma, 333 (5.8%) presented with DM. The most common DM site was the lung (57.1%), followed by bone (46.8%) and liver (19.5%). DM was most common in adenocarcinoma-not otherwise specified (15.1%, 132/874) and salivary duct carcinoma (10.4%, 30/288). High-grade mucoepidermoid carcinoma had the highest rate of lung metastases (81.6%, 31/38). Conversely, myoepithelial carcinoma had the highest rate of bone metastases (85.7%, 6/7). DM at presentation was independently associated with an increased mortality risk (hazard ratio, 1.62; 95% CI, 1.40-1.90).
Conclusion: We identified a DM rate of 5.8% in MSG malignancy at presentation. Overall 43% of patients presented without DM to the lung but with DM to the bones, liver, and/or brain. The most common metastatic sites differed by tumor histology. Staging with computed tomography neck and chest alone may fail to detect sites of DM; this work can be used for patient counseling in the clinical setting.
Keywords: distant metastasis; outcomes; salivary gland cancer.