Treatment outcomes of definitive radiotherapy for unresectable salivary gland cancers: a multicenter, retrospective study in northern Japan.

Background: Treatment of unresectable salivary gland cancers is challenging. This multicenter, retrospective study aimed to evaluate the treatment outcomes of definitive radiotherapy, with or without chemotherapy, for locally advanced, unresectable, salivary gland cancers.

Methods: A total of 27 patients with unresectable salivary gland cancers who underwent concurrent chemoradiotherapy or radiotherapy with curative intent between 2012 and 2022 at 13 hospitals in northern Japan were included in this study. Overall survival (OS) and progression-free survival (PFS) were assessed, and factors affecting OS and PFS were identified through univariate and multivariate Cox regression analyses. The variables evaluated included age, sex, primary site, histological type, clinical T and N status, clinical stage, treatment type, and radiation type.

Results: Seven patients received concurrent chemoradiotherapy, and 20 patients received radiotherapy (6 photon, 11 proton, 3 heavy ion). With a median follow-up period of 28 months, the three-year OS and PFS rates for the 27 patients were 54.4% and 27.8%, respectively. Patients who received concurrent chemoradiotherapy had better PFS than those who received radiotherapy alone (HR 0.16, 95% CI 0.03-0.81, P = .026).

Conclusions: Definitive radiotherapy for locally advanced, unresectable, salivary gland cancers resulted in relatively good outcomes. Concurrent chemoradiotherapy was associated with better PFS than radiotherapy.