Skip mediastinal lymph node metastasis and lung cancer: a particular N2 subgroup with a better prognosis

Lymph node (LN) metastases from lung cancer may skip the intrapulmonary nodes directly to the mediastinum ([N1-]N2 vs [N1+]N2). This phenomenon is frequent. Patients with such a metastatic pattern appear to have a better prognosis following surgery. Our purpose was to further study the clinical significance and prognostic value of this particular group of (N1-)N2 patients.

We retrospectively analyzed the data of 731 patients with a pN2 stage who underwent resection for non-small cell lung cancer. Patients with (N1-)N2 metastases (n = 209) were compared to patients with intrapulmonary (N1+)N2 (n = 522).

In the (N1-)N2 group, lobectomies were more frequent (54% vs 33%, p = 0.00), metastases more frequently involved a single LN station (79.4% vs 56.3%, p < 0.000001), and primary tumor was more often located in the upper lobes (67.4% vs 55.6%, p = 0.0066). (N1-)N2 was a factor of better prognosis (5 year survival rates 34.4% vs 18.5%, p = 0.00006), which proved also significant when only a single station was involved (38.4% vs 24%, p = 0.0005). These results were confirmed by multivariate analysis.

(N1-)N2 skip metastasis is a unique subgroup of pN2 disease. Lung lymph drainage anatomy may explain the occurrence of these metastases. They form an independent prognostic factor of survival suggesting the need for further study, the results of which may lead to better knowledge of lung cancer, improved classification, and adapted adjuvant therapy.