Predicted outcomes of subdividing M1-stage metastatic lung cancer based on the prognosis and the response to local consolidative therapy

BACKGROUND: For stage IV non-small cell lung cancer (NSCLC) patients, systemic therapy is the main strategy, and local consolidative therapy tends to be performed for patients with oligometastases. The porpose of this article is to evaluate the prognostic effects of local consolidative therapy for patients with stage IV NSCLC and divide these patients into different subcategories to stratify the prognoses. METHODS: A total of 30,583 patients with stage IV NSCLC were identified in the Surveillance, Epidemiology, and End Results (SEER) database. To identify factors related to high cancer-specific mortality (CSM) rates and compare the prognostic effects of different treatment strategies, a competing risk model was developed. Furthermore, independent prognostic factors identified through multivariable analysis were employed to supplement the current M1 subcategory. Cumulative incidence curves were estimated using the Kaplan-Meier method, and the log-rank test was used to compare prognostic differences. RESULTS: The CSM rates of M1a, M1b, and M1c patients were significantly different [M1b versus M1a: subdistribution hazard ratio (SHR), 1.38; 95% confidence interval (CI), 1.31–1.45; P<0.001; M1c vs. M1a: SHR, 1.76; 95% CI, 1.67–1.85; P<0.001]. Patients were divided into five groups depending on the M1 subcategory and liver involvement (Group A, M1c NSCLC with liver involvement; Group B, M1c NSCLC without liver involvement; Group C, M1b NSCLC with liver involvement; Group D, M1b NSCLC without liver involvement; and Group E, M1a NSCLC). Univariable analysis showed that liver involvement was associated with increased cancer-specific mortality (CSM) rates in both M1b and M1c patients (A vs. B: SHR, 1.36; 95% CI, 1.30–1.43; P<0.001; C vs. D: SHR, 1.27; 95% CI, 1.20–1.35; P<0.001). Primary tumor surgery plus chemotherapy may substantially benefit patients, especially M1b patients (surgery alone: SHR, 0.425; 95% CI, 0.361–0.500; P<0.001 vs. chemotherapy alone: SHR, 0.366; 95% CI, 0.352–0.382; P<0.001 vs. chemotherapy plus surgery: SHR, 0.194; 95% CI, 0.165–0.228; P<0.001; no treatment used as reference). CONCLUSIONS: Subdivision of M1 disease and awareness of liver involvement may help to inform the prognosis of stage IV NSCLC patients and facilitate treatment planning.