Prognostic impact of examined mediastinal lymph node count in clinical N0 non-small cell lung cancer

OBJECTIVES: The number of examined mediastinal lymph nodes (mLNs) could represent the quality of mediastinal lymphadenectomy for non-small cell lung cancer (NSCLC). This study aimed to evaluate the prognostic impact of the number of examined individual mLNs in patients with resectable NSCLC. METHODS: We retrospectively evaluated 1420 patients with clinical stage IA-IIB, N0 NSCLC who underwent complete resection by lobectomy, which involved hilar and mLN dissection, between 2008 and 2016. We investigated the threshold number of examined mLNs that had prognostic significance and evaluated their effects on the risk of mLN recurrence. RESULTS: In a respective multivariable analysis according to the number of examined mLNs, examining >= 3 mLNs [reference (ref.) mLNs <= 2] achieved statistical significance and had the best prognosis (hazard ratio, 0.68; P = 0.013). In the multivariable analyses for each pathological N (pN) stage, >= 3 examined mLNs (ref. mLNs <= 2) were an independent prognostic factor in pN1 disease (hazard ratio, 0.32, P = 0.002), but not in pN0 or pN2 disease. The cumulative incidence of mLN recurrence was significantly lower in patients with >= 3 examined mLNs (ref. mLNs <= 2, hazard ratio, 0.27; P = 0.008) in pN1 disease. Patients with >= 3 examined mLNs had higher upstaging rates to pN2 than those with <= 2 examined mLNs. CONCLUSIONS: Examining >= 3 mLNs contributed to a favourable prognosis and low mLN recurrence risk in patients with clinical stage I-II, N0 NSCLC. Our findings can serve as a benchmark for the number of required mLNs to be examined.