Yang MZ, et al. - Researchers assessed a total of 2292 cases seen between January 2001 and December 2014 to investigate the incidence and distribution of mediastinal lymph node metastases (MLNM) in non-small-cell lung cancers (NSCLC) 3 cm or less, with the purpose of guiding mediastinal lymph node dissection. For different primary tumor lobes, following were the most common mediastinal metastatic sites: right upper lobe, 17.7% (87/492) for level 4R; right middle lobe, 14.9% (28/188) for level 7; right lower lobe, 19.8% (82/414) for level 7; left upper lobe, 18.2% (96/528) for level 5; and left lower lobe, 16.6% (42/253) for level 7. This indicates that for those tumors that are 3 cm or less, different primary NSCLC lobe locations have a different propensity to be sites of MLNM. A lower zone mediastinal lymph node dissection appears unnecessary for upper lobe tumors and an upper zone mediastinal lymph node dissection seems unnecessary for lower lobe tumors when tumours were no larger than 1 cm.