ESTRO 2025 - Abstract Book

S1022

Clinical – Head & neck

ESTRO 2025

Purpose/Objective: This study sought to clarify the incidence and outcome of distant metastasis (DM) in patients with major salivary gland cancer who received upfront surgery followed by adjuvant postoperative radiation therapy (PORT). Material/Methods: A total of 214 patients who were enrolled in Korean Radiation Oncology Group multicenter study were analyzed for this study. The histologies of salivary gland cancer were mucoepidermoid carcinoma (MEC) (n=63), adenoid cystic carcinoma (ACC) (n=43), salivary duct carcinoma (SDC) (n=27), carcinoma ex-pleomorphic adenoma (Ca-ex-PA) (n=20), adenocarcinoma (Adenoca) (n=14), acinic cell carcinoma (AC) (n=12), squamous cell carcinoma (SQ) (n=11), basal cell carcinoma (BSC) (n=5), epithelial-myoepithelial carcinoma (EMC) (n=5), myoepithelial carcinoma (n=3), oncocytic carcinoma (n=2), carcinoma with squamous differentiation (n=1), lymphoepithelial carcinoma (n=1), non-small cell carcinoma (n=1), polymorphous low grade adenocarcinoma (n=1), small cell carcinoma (SCC) (n=1) and others (n=4). Median total RT doses, number of fractions and fractional doses were 61 (range, 26-70) Gy, 33 (range, 13-38) and 1.8 (range, 1.8-2.5) Gy, respectively. Concurrent and adjuvant chemotherapy was administerd in 3 (1.4%) and 5 (2.3%) patients, respectively. Results: With median follow-up of 74 (range, 4-174) months, DM developed as a first (n=44) or second relapse event (n=4) in a total of 48 (22.4%) patients. When we examined the incidence of DM as a first failure in each histological subtype, high incidence of DM was found in SCC (100%), SQ (45.5%), ACC (40.5%), Adenoca (35.7%), SDC (30.8%), Ca-ex-PA (26.3%) and others (25%). In univariate Kaplan-Meier analysis, histological subtype (p < 0.001), salivary gland subsite (p = 0.002), pathological T-stage (p = 0.001), pathological N-stage (p <0.001), perineural invasion (p = 0.001), extracapsular extension (p = 0.001), lymphovascular invasion (p =0.001) and resection margin status (p = 0.009) significantly affected distant metastasis-free survival (DMFS). Among population with major histological subtypes, DMFS outcomes were significantly divided into two groups; superior outcomes in AC, BSC, EMC and MEC subtypes and inferior outcomes in Adenoca, Ca-ex-PA, SDC and SQ subtypes. The 5-year DMFS rates in each group were as follows; 100% (AC), 100% (BSC), 100% (EMC) and 96.6% (MEC) in superior group and 62.5% (Adenoca), 72.6% (Ca-ex PA), 68% (SDC) and 54.5% (SQ) in inferior group. Conclusion: Notwithstanding the varied histological composition, we observed different DM incidence and DMFS outcomes according to histological subtypes in salivary gland cancer patients who underwent upfront surgery and PORT. Although clinical outcomes were comparable to histological series, there seems to be opportunity for improvement in systemic controls in high-risk histological subtypes.

Keywords: Radiation therapy, Salivary gland cancer

References: 1. 2021 Wang et al. Clinicopathological Factors are Predictors of Distant Metastases From Salivary Gland Carcinoma After Surgery Combined With 125I Internal Brachytherapy 2. 2024 Aral et al. Evaluation of the efficacy of adjuvant radiotherapy versus chemoradiotherapy in patients with salivary gland tumor