Adjuvant therapy in the management of operable salivary duct carcinoma: correlating evidence with a retrospective review

Background: Salivary duct carcinoma (SDC) is an extremely rare and aggressive subtype of salivary gland cancer with high morbidity and mortality and poor response to treatment. The current options of treatment include radical surgery followed by radiotherapy (RT) with or without chemotherapy. The aim of this study was to analyse the patterns of recurrences, possible predictors of outcome and role of RT in a cohort of patients with non-metastatic SDC. Methods: A retrospective review of patients treated between 2010 and 2019 with histologically proven non-metastatic SDC was conducted. Results: Sixteen patients were included in the series. Median follow-up was 25 months. Progression-free survival (PFS) and overall survival (OS) at 12 months were 61% and 80%, respectively. Seven out of the 16 patients had disease progression, distant metastases being most frequent. Four patients died due to disease progression. PFS was significantly worse for patients with pathological neck node positivity (p = 0.036) and peri-parotid nodes (p = 0.007). Local control was significantly associated with RT (p = 0-011). Addition of any chemotherapy, regardless of either concurrent or adjuvant, had no impact on the PFS or OS. Pathological neck node positivity with nodal stage of N2 or higher correlated significantly with worse OS (p = 0.031). Conclusion: Salivary ductal carcinoma is an aggressive malignancy with high metastatic potential. Inferior prognosis was observed among patients who had metastatic deposits in either cervical nodes or peri-parotid nodes on histopathology. As systemic failures are more predominant among these patients, larger prospective trials are needed to formulate an optimum strategy for choice and sequencing of first-line systemic therapy.