Efficacy
There are no randomised clinical trials to support the use of post-operative radiation therapy (PORT) for resected major salivary gland carcinoma. Until the publication of the 2021 ASCO guidelinesr, there was also a lack of consensus guidelines. Multiple large database studiesrrrrrr as well as several institutional cohort studiesrrrrr support the role of PORT in both improving local/locoregional control (LRC) as well as overall survival (OS) in selected patients with salivary gland tumours.
Local control rates
Regarding major salivary gland malignancies, several large institutional and population based studies series report improved local/LRC with the addition of radiation therapy (RT) to surgery.rrr Hanson et al report 5 year local recurrence free survival rates (LRFS) in patients treated with surgery with or without adjuvant radiation therapy; 94% (negative margins), 90% (close margins) and 75% (positive margins).r PORT was associated with improved local control (LC) (HR 0.34, 95% CI: 0.13-0.89). Subgroup analysis found that in low/intermediate risk histologic group patients with close margins, PORT was not associated with improved LC (HR 0.66, 95% CI: 0.07-6.34). Even in the patients with positive margins, those with tumours of low-risk histologic group had 10 year disease specific survival (DSS) 100% and LC 89%.
Figure 1: Local Recurrence-Free Survival Stratified by Postoperative Radiation for Low- and Intermediate-Risk Histologic Groups With Close Margins: Low-risk (A) and intermediate-risk (B) groups.r
© JAMA Otolaryngol Head Neck Surg, 2022r
Overall survival
Four national database studies suggest increased OS with addition of PORT to surgery for salivary gland cancer.rrrr Cheraghlou et al. reported on 8580 patients from the National Cancer Database (NCDB) and found PORT improved OS for salivary gland tumours with adverse features (any one of adenoid cystic histology, intermediate/high grade, positive surgical margins, or pathologic node involvement) for both early-stage (AJCC stage 1-2) Hazard ratio (HR) : 0.744, p=004 and late-stage (AJCC stage 3-4) HR: 0.688, p<001) disease.r The addition of chemotherapy for the latter group did not affect survival (HR: 1.028, p=0.705).
Figure 2: Survival associated with adjuvant RT for propensity-score matched cohort by patient risk groupr (Note: The late-stage without adverse feature group did not have sufficient numbers to include in this analysis)
© Head Neck, 2018r
The benefit for adjuvant RT for low grade disease with close margins remains inconclusive. North et al. report on patients in the NCDB with intermediate-grade, early T-stage, node negative parotid carcinoma and found PORT was associated with improved OS in patients with positive margins when adjusted for age, insurance status and extent of parotidectomy (HR 0.34, 95% CI: 0.13-0.88), but not in the setting of negative margins (HR 1.02, 95% CI: 0.53-1.93).r
Figure 3: The influence of adjuvant RT on overall survival of patients with (A) negative margin resections and (B) positive margin resections when adjusted for age, insurance status and extent of parotidectomyr
© Am J Otolaryngol, 2019r
Histology specific data
Regarding histology specific data, there have been multiple large databases and/or institutional series looking specifically at adenoid cystic carcinoma, mucoepidermoid carcinoma, lymphoepithelial carcinoma, ex pleomorphic adenoma, acinic cell carcinoma and salivary duct carcinoma.rrrrrrrr Although these national database studies provide large patient numbers, limitations of the NCDBrand SEERr studies include lack of reporting of local/locoregional progression free survival, lack of granularity of RT detail, and inability to control for multiple significant confounders, in particular selection bias regarding the use of PORT.
Chemotherapy
There is no evidence for administration of concurrent chemotherapy in this cohort, and it is not recommended outside a clinical trial.rr r