Omission of radiotherapy to lymph node level III in patients with cN0 adenoid cystic carcinoma of the major salivary gland: a single center experience

Purpose Due to the rarity of adenoid cystic carcinoma (ACC) of the major salivary gland, there is no consensus on the extent of prophylactic neck irradiation (PNI) for patients with clinically negative lymph nodes (cN0) disease. Materials and methods We conducted a retrospective analysis of all patients with ACC of the major salivary gland who received treatment at our center between January 2010 and April 2020. The primary endpoint was regional failure-free survival (RRFS). Secondary endpoints included overall survival (OS), distant metastasis-free survival (DMFS), local recurrence-free survival (LRFS), and acute toxicity. Results A total of 139 patients were included in the analysis. For cN0 patients, the 5-year RRFS, OS, DMFS, and LRFS were 93.2%, 90.2%, 75.7%, and 91.4%, respectively. Multivariate analysis revealed that PORT was an independent prognostic factor for RRFS and LRFS. No statistically significant differences were observed between the Level III sparing PNI group and the Standard PNI group in terms of RRFS, OS, DMFS, and LRFS. The doses delivered to the larynx and thyroid in the Level III sparing PNI group were significantly lower than those in the Standard PNI group. Conclusion In patients with cN0 ACC of the major salivary gland, PNI improves regional control, and the level III nodal region sparing radiotherapy does not increase the risk of level III recurrence, while potentially reducing toxicity.