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

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.