Skip metastasis to the mediastinal lymph nodes in non-small cell lung cancer

Background. Whether any difference exists in clinical characteristics between resected non-small cell lung cancer with either skip or ordinary mediastinal lymph node metastases (N2 disease) needs to be clarified. Methods. There were 110 patients with stage IIIA N2 disease. Thirty-three patients demonstrating no metastasis at the hilar nodes [skip (+) group]were compared with the other 77 patients [skip (−) group]. To investigate the extent of nodal involvement, we classified the mediastinal lymph nodes into three regions (superior, inferior, or aortic). Results. There were no significant differences regarding histologic type, T status, or the site of the primary tumors between the skip (+) and the skip (−) N2 groups. In the skip (+) group, mediastinal node metastasis was found in only one region (level 1) in 30 patients (90.9%) and in two regions (level 2) in 3 (9.1%), whereas 28 patients (36.4%) from the skip (−) group revealed mediastinal metastasis at two or three regions (level 2 or 3). The overall survival rate at 5 years after operation was 35% in the skip (+) group and 12.7% in the skip (−) group (p = 0.054). This favorable clinical outcome in the skip (+) group could be explained partially by the higher proportion of patients with level 1 metastases. Furthermore, regarding patients with level 1 disease, the skip (+) group tended to have a better prognosis than the skip (−) group (p = 0.096). Conclusions. These results suggest that patients with skip mediastinal lymph node metastases represent a unique subgroup of N2 disease.