Prognostic significance of ratio of positive lymph nodes in patients with operable major salivary ductal carcinoma

Background Major salivary duct carcinomas (MSDCs) often involve the regional lymph nodes (LNs). However, the clinical value of LN parameters in patients with MSDCs is unclear. We aimed to investigate the optimal cut‐off points for number of positive LNs (PLNN) and ratio of positive LNs (PLNRs) and their prognostic value in patients with MSDC. Study Design Retrospective cohort. Methods We retrospectively reviewed relevant data extracted from the Surveillance, Epidemiology, and End Results database on patients with MSDC who had undergone surgery between 2004 and 2016. The optimal PLNN and positive lymph node ratio (PLNR) cut‐off points were identified using the X‐tile program. Kaplan–Meier and Cox regression analyses were performed to determine prognostic factors. Results Overall, 290 patients were enrolled, 57.6% of whom had LN metastases. Advanced T stage in the submandibular gland and unpaired lesions were associated with LN involvement. Positive LNs, late T stage, and submandibular gland location were associated with poor overall survival (OS). The 5‐year OS rates of patients with negative and positive LNs were 74.3% and 36.5%, respectively. PLNN > 16 and PLNR > 0.48 were the best cut‐off points. The 5‐year OS of patients with PLNN ≤ 16 and PLNN > 16 was 42.8% and 15.4%, respectively. The 5‐year OS rates were 46.8% for patients with PLNR ≤ 0.48 and 26.3% for patients with PLNR > 0.48. PLNR was a strong prognostic factor for patients with MSDC with LN metastases. Conclusions PLNR reflects both the effects of LN dissection and PLNN. Furthermore, its prognostic value in patients with MSDC exceeds that of PLNN. Patients with high PLNRs should be followed closely after surgery. Advanced T stage, submandibular gland location, and unpaired lesions were associated with lymph node involvement. The prognosis of SDC patients with PLNR ≤ 0.48 was better than that of SDC patients with PLNR > 0.48. PLNR can reflect both the effect of lymph node dissection and the number of positive lymph nodes, and its prognostic value for major SDC exceeds the number of positive lymph node number. Patients with high PLNR should be followed closely after surgery.