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

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Abstract
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.

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