Positive lymph nodes predict distant metastasis of salivary duct carcinoma after postoperative radiotherapy

Abstract Purpose Salivary duct carcinoma (SDC) is a high-grade subtype of salivary gland malignancy. Distant metastasis was the common pattern of failure for patients receiving surgery and adjuvant radiotherapy. We are aimed to analyze the prognostic value of positive lymph nodes for distant metastasis in the SDC following postoperative radiotherapy. Patients and Methods : We reviewed the data of patients with SDC receiving surgical resection and radiotherapy. The univariate analysis was conducted using Log-rank method for the clinicopathological features with distant-metastasis-free survival (DMFS). The multivariable analysis was performed by Cox regression hazards method. A risk stratification model was established by the score calculated with the variables qualified by multivariate P < 0.05. Results 91 patients were enrolled, and the median age at diagnosis was 58.5 years. 53.8%(n = 49) of the patients appeared with the involvement of neck lymph nodes after surgery. The advanced T stage (95% CI 1.325–5.38; P = 0.006), number of positive lymph nodes (PLN ≥ 8) (95% CI 1.241–6.58; P = 0.013), and peripheral invasion (PNI) (95% CI 1.059–4.65; P = 0.034) were significantly associated with DMFS for the SDC in the multivariate analysis. Patients were divided into two subgroups based on the risk factors, while significant differences of DMFS and OS were observed between the risk cohorts (5-year DMFS:35% vs.64.4%, P = 0.0001; 5-year OS:53.6% vs.70.4%; P = 0.048). Conclusion Higher number of positive lymph nodes was associated with worse DMFS in SDC following PORT. The patients at high risk appeared with significantly poor DMFS and survival, and clinical trials on adjuvant therapy are warranted for this subgroup.