The influence of grade on mortality risk in salivary gland malignancy

e18100 Background: Salivary malignancies are amongst one of the most difficult malignancies to classify.Currently, the impact of histologic variants has not been well described. The objective of this study was to evaluate histologic subtype and grade in salivary cancer staging. Methods: Salivary cancer histologies were collected from the National Cancer Database (NCDB) and the Surveillance, Epidemiology, and End Results (SEER) database. Multivariable models were used to adjust for clinicopathologic covariates and assess for relationships between histologic subtype, grade, and survival. Results: Histologic variants have a wide range of mortality risk (e.g., acinic cell carcinoma has a favorable 5-year survival, in opposition to salivary duct carcinoma) on univariate analysis(p < 0.001). Using multivariable analysis, the survival differences disappeared. However, worsening grade corresponded signficantly with deteriorating survival (5-year OS of 89% [95% CI 88-90%] (low-grade), 81% [95% CI 79-82%] (intermediate-grade), 45% [95% CI 44-47%] (high-grade) (p < 0.001)), on both multivariable analysis and propensity score matching. Recursive partitioning analysis incorporating grade into current staging generated a TNM+G schema (c-index 0.75, 95% CI 0.745-0.755) superior to the existing system (c-index 0.73, 95% CI 0.723-0.736). Conclusions: Grade is a significant factor in determining mortality risk in salivary cancers. Including grade into staging will improve current staging systems.