Mediastinal lymph node metastasis pattern of subsolid non-small cell lung cancer

Lymph node (LN) dissection is important in lung cancer surgery. LN metastasis was analyzed in each stage of non-small cell lung cancer (NSCLC) to inform the resection strategy, especially for subsolid nodules. This study aimed to explore LN metastasis distribution features of NSCLC, with a focus on subsolid nodules.

Patients with NSCLC treated from January 2014 to December 2018 (n=6,273) were retrospectively grouped according to primary tumor locations and clinical stages. The incidence and distribution of LN metastasis were analyzed.

Clinical and pathological characteristics varied with different primary lesion locations. LN metastasis occurred in 1,356 patients (21.62%). Lobe-specific distribution was observed on mediastinal LN metastasis. However, LN metastasis in each region exceeded 5%, which warrants careful attention during surgical dissection. Subgroup analysis indicated more regular lobe-specific distribution in cT1N0 lesions, but not in advanced stages. LN metastasis was negligible (<1%) in subsolid nodules (≤3 cm) with radiographic consolidation-to-tumor ratio (CTR) ≤0.5, but significant in the CTR >0.5 group (2.34-6.60%) in each mediastinal region. For upper lobe tumors, upper mediastinum was invaded frequently (right, 4.34%; left 5.70%). In right middle lobe, the mediastinal (5.21%) or sub-carinal (6.06%) region was involved. Tumor invasion in lower lobes included the upper (left, 3.38%; right, 2.49%), sub-carinal (right, 5.88%; left, 4.00%) and lower (right, 2.34%; left, 2.33%) regions. Prognosis was significantly better in the CTR ≤0.5 group compared to the CTR >0.5 group (P<0.0001).

Subsolid tumors with CTR ≤0.5 demonstrate an extremely low risk of mediastinal LN metastasis, which may help guide individualized lymphadenectomy strategies. For tumors with CTR >0.5, metastatic risk is significantly higher, suggesting more comprehensive LN evaluation may be warranted.