The Current Position of Postoperative Radiotherapy for Salivary Gland Cancer: A Systematic Review and Meta-Analysis

Simple Summary Given the low incidence, heterogeneous behavior, and diverse anatomical sites of salivary gland cancer (SGC), there are a limited number of clinical studies on its management. This is the first systematic review and meta-analysis to report the cumulative evidence on postoperative radiotherapy (PORT) for SGC of the head and neck. Based on 2962 patients with SGC from 26 studies, this study demonstrated the long-term survival and toxicities of PORT as a local treatment modality for SGC. Considering the suboptimal disease-free survival and distant metastasis-dominant recurrent patterns, however, an intensified treatment strategy is needed.Abstract Background: Because of the rarity, heterogeneous histology, and diverse anatomical sites of salivary gland cancer (SGC), there are a limited number of clinical studies on its management. This study reports the cumulative evidence of postoperative radiotherapy (PORT) for SGC of the head and neck. Methods: A systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. We searched the PubMed, Embase, Cochrane Library, and Web of Science databases between 7th and 10th November 2023. Results: A total of 2962 patients from 26 studies between 2007 and 2023 were included in this meta-analysis. The median RT dose was 64 Gy (range: 56-66 Gy). The median proportions of high-grade, pathological tumor stage 3 or 4 and pathological lymph node involvement were 42% (0-100%), 40% (0-77%), and 31% (0-75%). The pooled locoregional control rates at 3, 5, and 10 years were 92% (95% confidence interval [CI], 89-94%), 89% (95% CI, 86-93%), and 84% (95% CI, 73-92%), respectively. The pooled disease-free survival (DFS) rates at 3, 5, and 10 years were 77% (95% CI, 70-83%), 67% (95% CI, 60-74%), and 61% (95% CI, 55-67%), respectively. The pooled overall survival rates at 3, 5, and 10 years were 84% (95% CI, 79-88%), 75% (95% CI, 72-79%), and 68% (95% CI, 62-74%), respectively. Severe late toxicity >= grade 3 occurred in 7% (95% CI, 3-14%). Conclusion: PORT showed favorable long-term efficacy and safety in SGC, especially for patients with high-grade histology. Considering that DFS continued to decrease, further clinical trials exploring treatment intensification are warranted.