Adoption of Adjuvant Chemotherapy in High-Risk Salivary Gland Malignancies

Abstract

<h3>Purpose/Objective(s)</h3> Surgical resection and radiation therapy remain the primary modalities of treatment for patients with salivary gland malignancies. The role of adding adjuvant concurrent chemoradiotherapy (CRT) versus radiotherapy (RT) alone in this group is currently under investigation in a clinical trial (RTOG 1008). We investigated the patterns of care and adoption of adjuvant chemoradiotherapy in treatment of high-risk salivary malignancies. <h3>Materials/Methods</h3> All adult patients in the National Cancer Database (NCDB) with salivary gland malignancies diagnosed from 2004 to 2018 were identified. Patients with unspecified squamous cell carcinoma or with distant metastases were excluded. High-risk pathological features in this study were defined as positive surgical margins, lymphovascular invasion, regional lymph node spread, grade 2-4, and stage T3-4. The proportion of patients receiving adjuvant CRT was calculated per year. Linear regression analysis was performed on the CRT:RT proportion across the study period. Kaplan-Meier survival analysis was performed on a sample of propensity score-matched patients based on age, sex, tumor histology, staging, margins, and comorbidities. <h3>Results</h3> During the study period, 33,262 adult patients with salivary gland malignancies were identified. Among those patients, 17,361 (52.2%) patients received adjuvant RT, of which 3,333 (19.2%) received concurrent chemotherapy. Among the patients who received RT, 13,891 (80.0%) had high-risk features, of which 3076 (22.1%) received concurrent chemotherapy. The proportion of patients receiving chemotherapy across all pathologies increased from 18% to 28% (p<0.001) over the study period. Use of chemotherapy in high-risk patients increased from 21% to 35% (p<0.001). Among different histologies, significant increases were seen in acinic cell carcinoma (2% to 14%, p<0.001), adenoid cystic carcinoma (8% to 15%, p<0.001), and adenocarcinoma (27% to 51%, p<0.001); but no increases in mucoepidermoid carcinoma (16% to 17%, p=0.47) and carcinoma ex pleomorphic adenoma (20% to 34%, p=0.27) were observed. In a 213 propensity score-matched population, no significant difference in overall survival (p=0.4) was observed between patients who received chemotherapy and those who did not. <h3>Conclusion</h3> While no clinical trial data is available, a significant increase in the use of adjuvant CRT is seen in patients with salivary gland malignancies with or without high-risk features, and in certain histologies. We could not identify any associated survival benefit in this patient population. The upcoming trial (RTOG 1008) could determine if there is a benefit in adding chemotherapy to adjuvant radiotherapy.