The incidence and distribution of mediastinal lymph node metastasis and its impact on survival in patients with non-small-cell lung cancers 3 cm or less: data from 2292 cases

Our goal was 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.A total of 2292 cases seen between January 2001 and December 2014 were included. These patients were grouped according to the lobes with the primary tumours. The incidence and distribution of pathological MLNM were compared among the groups. The impact of MLNM on overall survival was also compared.The most common mediastinal metastatic sites for different primary tumour lobes were as follows: 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. For patients with tumours in the upper lobe, the median survival time was 32 months for those with MLNM in the subcarinal zone or lower zone compared with 83 months for those with MLNM only in the upper zone (P < 0.01). When the tumours were 1 cm or less, the incidence of MLNM to the lower zone for upper lobe tumours and of MLNM to the upper zone for lower lobe tumours was zero.Different primary NSCLC lobe locations have a different propensity to be sites of MLNM for those tumours that are 3 cm or less. For tumours no larger than 1 cm, a lower zone mediastinal lymph node dissection might be unnecessary for upper lobe tumours and an upper zone mediastinal lymph node dissection might be unnecessary for lower lobe tumours.