To investigate the status of intrapulmonary lymph node metastasis and its impact on pathological staging in patients with non-smallcell lung cancer (NSCLC).

A total of 177 patients undergoing lobectomy or pneumonectomy and systemic lymph node dissection for lung cancer inDepartment of Thoracic Surgery, Tianjin Chest Hospitalbetween January 2015 and March2016 were selected. A special pathological examination protocol on lobar lymph nodes (No. 12) and segmental lymph nodes (No. 13) surgical specimens was conducted after routine pathological examination. The N stage retrieved by special pathological examination protocol was compared with thatobtainedby routine pathological examination. In addition, the risk factors of the intrathoracic lymph node metastasis were explored.

A total of 1268 N1 lymph nodes were examined, among which 736 were detected during routine pathological examination protocol and 532 were retrieved byspecial pathological examination protocol. The combination of routine pathological examination and special pathological examination provided a median of 7 N1 lymph nodes(range, 2 to 24), a significant increase from the number of N1 lymph nodes examined by routine pathological examination alone(4; range, 0 to 18)(P<0.001). The combination of routine pathological examination and special pathological examination led to detection of a total of 240 N1 lymph nodes with metastasis, with a median of zero (range, 0 to 7; 75th percentile, 1; 90th percentile, 3), and the number of detected lymph node metastasis was significantly higher than that in routine pathological examination alone(range, 0 to 5; 75th percentile, 0; 90th percentile, 2)(P<0.001). Stratification analysis showed surgical approach, tumor location, pathology type, tumor size and mediastinal lymph node metastasis had correlation with the metastasis of lobar lymph nodes(No. 12) and segmental lymph nodes (No. 13)(P<0.05), while age, sex and vascular cancer embolus did not(P>0.05). The pathological stage of 15 patients(8.4%) changed from N0 to N1 after specialpathological examination.

Routine pathological practice frequently leaves a large number of N1 lymph nodes unexamined, a clinically significant proportion of which harbor metastasis. The special pathological examination protocol is suggested to improve the accuracy of pathological staging of NSCLC.