Role of skip metastasis to mediastinal lymph nodes in non-small cell lung cancer

Background: Skip metastasis to mediastinal lymph nodes is a well-known phenomenon in non-small cell lung cancer (NSCLC). Little is reported in the literature about its clinical importance. It is still under discussion whether any prognostic differences exist between resected NSCLC with either skip metastases or continuous mediastinal lymph node metastases (N2). Patients and Methods: We analyzed retrospectively the data of 45 patients with a pN2-stage, who underwent resection for NSCLC. Seventeen of these patients (37.8%), showing no metastatic involvement of hilar (N1) lymph nodes, were compared to the remaining 28 patients with infiltration of hilar nodes (N1) as well as N2 nodes. Results: Multivariate analysis showed no statistically significant difference between the skip metastasis and the continuous N2 group regarding sex, age, histology, T- or M-status. The frequency of skip metastasis was higher in patients with a primary tumor in the upper lobe (n = 12, 71%) compared to the lower lobe (n = 5, 29%). This difference was not statistically significant. In patients with a non-continuous lymph node spread, 29 out of 119 resected mediastinal lymph nodes were infiltrated (1.7 per patient, range: 1-10). Compared to 83 metastatic involved lymph nodes out of 198 resected mediastinal nodes (three per patient, range: 1 - 10) in patients with involvement of N1 and N2 nodes (P = 0.034, Mann-Whitney test). The 5-year survival rate of pN2 patients with skip metastasis was 41 % compared to 14% in patients with involvement of N1 and N2 nodes (P = 0.019). Conclusions: pN2 patients with mediastinal lymph node skip metastasis have a more favorable prognosis compared to pN2 patients with continuous infiltration of the regional lymph nodes. Patients with a continuous lymph node involvement show an increased number of infiltrated mediastinal lymph nodes per patient compared to patients with a non-continuous spread. 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.