Clinical and prognostic analysis of skip N2 metastases in stage IIIA-N2 non-small cell lung cancer

Abstract

To investigate the clinicopathologic factors and the distribution pattern of N2 lymph nodes, to analyze the relationship between the survival rate and skip metastasis of non-small cell lung cancer (NSCLC) patients. The clinical data of 478 patients with a pN2 stage who underwent resection for non-small cell lung cancer from January 2000 to December 2004 was retrospectively analyzed. Skip group and non-skip group were defined. Characteristics of tumors, ganglionar involvement and survival were analyzed in both groups. The incidence rate of skip N2 metastasis in stage IIIA-N2 NSCLC patients was 40.6%, which was correlated to sex, smoking and the type of histology (P < 0.05). Squamous carcinoma was the main type of skip group (chi² = 7.602, P = 0.022). The frequency of skip metastasis was higher in patients with a primary tumor in the upper lobe (57%) compared to the lower lobe (43%) (chi² = 5.097, P = 0.024). Superior nodes were more frequently involved by skip group (chi² = 7.046, P = 0.030). Moreover, the relationship between the primary tumor location and N2 positive lymph nodes were described as follows: right upper lobe cancer displayed skip-N2 nodal metastasis mostly in the 2nd, 3rd and 4th station, right middle and lower lobe mostly in the 7th station, left upper lobe mostly in the 5th and 6th station (71.7%), and left lower lobe mostly in the 7th and 9th station. The 5-year survival rate of pN2 patients with skip metastasis was 22.1% compared to 13.6% in patients with involvement of N1 and N2 nodes (P = 0.001). Survival analysis showed that skip N2 metastasis was an independent risk factor of stage IIIA NSCLC. The frequency of skip metastasis was higher in patients with a primary tumor in the upper lobe and in the superior nodes. Skip metastasis is an independent prognostic factor of survival. The presence of skip metastasis seems to be a unique subgroup of pN2 disease in NSCLC.