Meta-analysis of postoperative radiotherapy versus radiochemotherapy for salivary gland cancer finds no significant survival differenceRadiotherapy alone may be as good as combined therapy for salivary gland cancer

There is a lack of prospective clinical trials on the therapy of salivary gland cancer (SGC) due the rarity and large variety of histological subtypes. This study aimed to compare overall survival (OS) after primary surgery of SGC followed by postoperative radiotherapy (PORT) versus radiochemotherapy (PORCT) in curative intent. A systematic review and meta-analysis were performed on studies reporting OS after the two postoperative therapy modalities using hazard ratios (HRs) or allowing to calculate the HRs from the data. These studies were identified from PubMed, Web of Science, and Cochrane Library databases until October 2024. Pooled HR with 95% confidence interval (CI) is reported with random-effects or fixed-effects models. The search yielded 1,074 publications, of which 11 retrospective clinical studies with 26,612 adult patients could be included. None of the studies found a statistically significant difference between PORT and PORCT. Likewise, this meta-analysis revealed no statistically significant difference between PORT and PORCT. The pooled HR based on a common effect model was 1.065 (CI: 0.998-1.137) with low between study heterogeneity (I²=24.1%) and heterogeneity variance τ = 0.009. A meta-regression only revealed one factor with influence on the HR. The proportion of T4 patients in the total study shows a HR = 1.153 for a 10% change 95% CI: 1.014,1.314). This meta-analysis, based on a highly confounded observational setting, does not permit a reliable conclusion as to whether PORCT leads to better OS than PORT as adjuvant therapy for patients with SGC. PORCT might be beneficial for high-risk subgroups. However, this was not possible to determine in this meta-analysis as all included studies were retrospective and heterogeneous leading to a high degree of uncertainty about the therapy effects. More robust data from high-quality cohort studies or randomized controlled studies are needed. There is an urgent need for alternative and more effective multimodal treatment concepts for SGC.