Abstract
INTRODUCTION: Contralateral lung tumors in non-small-cell lung cancer (NSCLC) are classified as stage M1a yet may represent hematogenous metastases or synchronous primary tumors. The impact of these tumors on overall survival (OS) is poorly understood. Here, we aim to determine whether NSCLC patients with M1a disease due only to a contralateral tumor nodule exhibit a favorable prognosis relative to other M1a or M1b patients. METHODS: Retrospective evaluation of the impact of contralateral tumor nodules on OS in NSCLC stratified by primary tumor size and N stage attained from Surveillance, Epidemiology, and End Results database. RESULTS: Of 173,640 patients, 5161 M1a-contra patients were identified. Median and 3-year OS for these patients exceeded that of patients with M1b (p < 0.0001) or other M1a disease (p < 0.0001). Primary tumor size and N stage were strongly associated with OS in M1a-contra patients. Three-year OS demonstrated a delayed convergence between M1a-contra and other M1a patients with primary tumors greater than or equal to 3 cm or mediastinal lymph node involvement. Proportional hazard modeling indicated that T1-2N0-1M1a-contra patients exhibit OS not significantly different (p = 0.258) from that predicted with comparable T and N stage disease plus a second early-stage primary. CONCLUSIONS: Contralateral tumors in NSCLC carry a more favorable prognosis than other M1a or M1b disease. Primary tumor size and N stage may help distinguish M1a-contra patients with hematogenous metastasis from those with a synchronous, second primary.