Characteristics of clinical N0 metastatic non-small cell lung cancer

Non-small cell lung cancer (NSCLC) patients who have clinically no mediastinal lymph node metastasis but have distant metastasis are occasionally found in clinical practice. Such clinical N0 metastatic NSCLC may be a different subtype from the clinical N1-3 patients with regional lymph node metastasis. The aim of this study was to evaluate the prognosis, clinical features, and incidence of clinical N0 NSCLC patients with metastasis.

All metastatic NSCLC patients (n=761) diagnosed at our hospitals from April 1999 to August 2012 were retrospectively analyzed. They were divided into two groups: N0 and N1-3. Staging was recorded according to the UICC 7th edition of the TNM classification. Differences between the two groups were analyzed using a Chi-square test. Prognostic factors were analyzed by the Kaplan-Meier method and Cox proportional hazards analysis. A probability value less than 0.05 was considered to be significant.

A total of 761 patients with NSCLC were registered. 124 patients (16.3%) were N0 and 637 (83.7%) were N1-3. There were no differences between the two groups in age, sex, smoking history, performance status, and histological type. The ratio of adrenal gland metastasis was low in the N0 group (N0 7.3%, N1-3 13.4%, p=0.002). Median survival time was longer in the N0 group (N0 11.9 months vs N1-3 7.2 months, p<0.001). N0 was an independent favorable prognostic factor.

Metastatic NSCLC patients with clinical N0 had a favorable prognosis and a lower ratio of adrenal gland metastasis than those with clinical N1-3. Our results suggest that a certain type of adrenal metastasis may result from direct lymphatic spread from a primary lung tumor. About one sixth of metastatic NSCLC cases are clinical N0. Therefore, clinical evaluations for detecting metastasis are important even in clinical N0 patients.