Treatment patterns and outcomes of palliative systemic therapy in patients with salivary duct carcinoma and adenocarcinoma, not otherwise specified

Background: Salivary duct carcinoma (SDC) and adenocarcinoma, not otherwise specified (adeno-NOS), are rare salivary gland cancers. Data on the efficacy of systemic therapy for these diseases are limited. Methods: Data were retrospectively collected from patients seen at The University of Texas MD Anderson Cancer Center during 1990 to 2020. Objective response rate (ORR) was assessed per RECIST v1.1. Recurrence-free survival (RFS), progression-free survival (PFS), and overall survival (OS) were assessed by Kaplan-Meier method. Cox regression model was performed to identify predictors of survival. Results: The analysis included 200 patients (110 with SDC and 90 with adeno-NOS); 77% had androgen-receptor-positive tumors and 47% had HER2-positive (2+-3+) tumors. Most patients without metastasis at diagnosis underwent surgery (98%) and postoperative radiotherapy (87%). Recurrence rate was 55%, and the median RFS was 2 years. Nodal involvement and positive surgical margins were associated with recurrence (P <.005). Among patients with stage IVA-B disease, addition of systemic therapy to local therapy increased OS (P =.049). The most-used palliative-systemic-therapy regimen was platinum doublet ± trastuzumab. For first-line therapy, the ORR and median PFS were 33% and 5.76 months, respectively, and for second-line therapy the ORR and median PFS were 25% and 5.3 months, respectively. ORR and PFS were higher with HER2-targeting agents. Median OS was 5 years overall and 2 years for metastatic disease. Older age and higher stage were associated with worse OS. Conclusion: Adding systemic therapy to local therapy may improve outcomes of patients with locoregionally advanced SDC or adeno-NOS. Except for HER2-targeted therapy, response to palliative systemic therapy is limited. These findings may be used as a benchmark for future drug development.