The significance of the characteristics of intra-thoracic lymph node metastasis for radiotherapy range in small cell lung cancer

Objective: To explore the reasonable radiotherapy range by analyzing the patterns and characteristics of intra-thoracic lymph node metastasis in small cell lung cancer (SCLC). Methods: One hundred and fifty patients with limited-stage SCLC who received radical resection of primary tumor and systemic intra-thoracic lymph node dissection were included in the study. All the lymph nodes in each area were recorded and examined pathologically to analyze the patterns and characteristics of intra-thoracic lymph node metastasis. Results: A total of 2372 lymph nodes were found in 631 areas,and a total of 413 positive lymph nodes (17.4%) were found in 188 lymph node areas (29.8%). Intra-thoracic lymph node metastasis were found in 88 patients,with a positive rate of 58.7%. The frequencies of metastasis in the area 11, 10, 7, 5, 4 were much higher than those in the other areas, and central located lesions and the higher T-stage lung tumors were more likely to develop intra-thoracic lymph node metastasis (χ2 =15.32, 39.72; P =0.000, 0.000, respectively). Tumors located in the right upper lobe and right middle/lower lobe had a higher tendency of metastasis to the areas 4, 7, 10 and 4, 7, 10, 11, respectively. Tumors located in the left upper lobe and left lower lobe had a higher tendency of metastasis to the areas 4, 5, 6, 10 and 4, 7, 9, 10, 11, respectively. Mediastinal lymph node metastasis (N2) were found in 72 patients, among whom 29 patients (40.3%) had skipping N2 metastasis without hilar metastasis. Tumors located in the upper lobe had a tendency of skipping metastasis to the upper mediastinum, while tumors located in the middle/lower lobe had a tendency of skipping metastasis to the upper and lower mediastinum. Conclusions: The lymph node metastases in SCLC follow the lymphatic drainage routes, that is, from intrapulmonary to the hilar and then to the mediastinum, but with some skipping metastases. Tumors located in different lobes have different high risk lymph node areas for metastasis, and elective irradiation to these lymph node areas maybe increase radiotherapy gain ratio in SCLC. (authors)