Post-operative radiotherapy in adenoid cystic carcinoma of salivary glands versus surgery alone: what is the evidence about survival and local control? A systematic review and meta-analysis

Abstract

Background: Adenoid cystic carcinoma of the salivary glands is a relatively rare malignancy characterized by slow growth and a poor prognosis, and effective treatments remain challenging to identify. This systematic review, following the PRISMA guidelines, aimed to analyze the potential benefits of post-operative radiotherapy in terms of local control of recurrences and survival advantages when compared with surgery alone in patients with adenoid cystic carcinoma.

Methods: A comprehensive systematic review was conducted by searching the MEDLINE, Cochrane, EMBASE, and OVID databases from January 1999 to July 2022. The goal was to identify articles comparing surgery alone with surgery plus postoperative radiotherapy for adenoid cystic carcinoma of the salivary glands. Downs and Black Checklist was used to assess the methodological quality and risk of bias of each included study. The data analysis was performed using Review Manager version 5.4.1.

Results: This review included 8 studies comprising a total of 3103 patients, divided based on the analyzed outcomes. The pooled odds ratio for overall survival at 5 years was 0.87 (95% confidence interval 0.43-1.76, p = 0.70), and at 10 years was 1.23 (95% confidence interval 0.69-2.16, p = 0.48). In both cases, no statistically significant differences were observed. However, the pooled odds ratio for local control at 5 years was 3.37 (95% confidence interval 1.35-8.42, p = 0.009), providing strong support for the use of post-operative radiation.

Conclusions: The findings from the meta-analysis suggest that post-operative radiotherapy significantly improves local control in patients with adenoid cystic carcinoma. However, there was no statistically significant increase in survival at 5 and 10 years. It is essential to note that the quality of the studies included in this meta-analysis ranged from fair to poor. To better clarify the indications for post-operative radiotherapy, future high-quality research is needed, particularly with improved stratification of patient groups. Additionally, it is important to recognize that achieving local control in adenoid cystic carcinoma is crucial for enhancing the overall quality of life for patients. We acknowledge that this review was not registered in the PROSPERO database, and the data pooling was conducted using a random effects model.

Keywords: Adenoid cystic carcinoma; Local control; Postoperative radiotherapy; Salivary glands; Survival.