Prognostic Implications of Occult Nodal Metastases in Patients with Clinically N0 Primary Parotid Gland Cancer.

The role of occult nodal metastases in patients with parotid gland cancers remains unclear; such metastases are histologically diverse and exhibit unpredictable clinical courses. Here, we evaluated the prognostic utilities of such metastases, including metastases in the intraparenchymal lymph nodes (PARs). We retrospectively reviewed the medical charts of patients who underwent surgery to treat clinically N0 primary parotid gland cancers from 2000 to 2022. The primary outcome variables were 5-year overall survival (OS) and 5-year disease-free survival (DFS). We explored the effects of occult nodal metastases, including metastases in the PARs, especially in terms of the pathological T (pT) classification. Among 74 patients, 48 (64.8%) were pT1/2 cases, and 26 (35.2%) were pT3/4 cases. Both perineural and lymphatic invasion were negatively associated with the 5-year DFS (hazard ratio [HR] = 3.533, 95% confidence interval [CI] = 1.325-9.421, = 0.012; HR = 4.028, 95% CI = 1.497-10.839, = 0.006, respectively). During pathological review, PAR metastases were observed in 12 patients (16.2%), and other occult metastases were present in 8 patients (10.8%). PAR metastases reduced the 5-year DFS in pT1/2 cases (87.2% vs. 22.2%, = 0.001) but not in pT3/4 cases. PAR metastases significantly reduced the 5-year DFS in patients with clinically N0 primary parotid gland cancer. On subgroup analysis according to pT classification, this effect was significant among patients with early pT1/2 status but not patients with advanced pT3/4 status.