Skip metastases: analysis of their clinical significance and prognosis in the IIIA stage of non-small cell lung cancer.

OBJECTIVE

To determine the clinical significance of skip metastases (pN2/S) in patients with resected pIIIA/N2 NSCLC. The incidence of pN2/S after mediastinal lymph node dissection (MLD) and sampling (MLS) were compared.

METHOD

From 1997 to 2000, 580 lung resections for NSCLC performed at our department. The 151 patients (26.5%) at stage IIIA/N2 (pN2+) were grouped according to their skip metastases status. Group A included the ordinary pN2 (pN2/O) cases (71%) and group B the pN2/S (29%). Age, gender, type of resection, right or left lesion, histology, tumor lobe predilection, MLD or MLS pathologic results, the level and the number of node stations involved and survival were analyzed.

RESULTS

In 44 patients (29%) pN2/S disease was present. Statistical analysis revealed significant difference between pN2/O and pN2/S for the following: (1) pN2/S was more common for right-sided lesions (P=0.007); (2) Squamous carcinoma was the main type of pN2/S (P=0.007) and (3) pN2/S was more frequently detected after MLD than after MLS (P=0.001). Although pN2/S involved more often upper mediastinal lymph nodes (Nos. 2, 3) and one station level (pN2/S: 41 vs. pN2/O: 19.6%, P=0.228) was not found statistically significant. pN2/O was more common after right upper lobectomy and pN2/S after right lower lobectomy. The 3-year survival was more favorable for the pN2/S group (A: 24 vs. B: 36%, P=0.07).

CONCLUSION

(1) MLD was found to be more reliable for pN2/S detection than MLS. (2) The presence of pN2/S proved to be a less aggressive form of lymphatic spread that should be taken into account in the future. (3) Strong correlation between right lower lobe tumors and pN2/S was demonstrated. (4) Different routes of cancer lymphatic spread between pN2/S and pN2/O are suggested.