Objective To investigate the impact of lymph node metastasis on the survival of SCLC patients with M1a disease.

Methods We retrospectively analyzed the medical records of 7027 SCLC patients with M1a disease from 2004 to 2015 in SEER database. The Kaplan-Meier method and log-rank test were used to estimate the OS in all N stage subgroups. Cox proportional hazard model was used to assess whether N stage was an independent risk factor for prognosis.

Results The median OS of all patients was 7 months. Among all M1a patients, the patients without lymph node involvement (N0) had the best OS, followed by N1 stage patients; N2 and N3 stage patients had the worst OS (P < 0.001). Similarly, this trend was observed when M1a disease was subdivided into contralateral pulmonary nodules, malignant pleural effusion and malignant pericardial effusion. Multivariate analysis showed that lymph node metastasis was an independent prognostic factor for SCLC patients with M1a disease, and this result was also noticed in all subgroups of M1a disease.

Conclusion Lymph node metastasis may affect the survival of SCLC patients with M1a disease, adding prognostic information. And it is recommended to further improve the N descriptor in the next version of TNM staging system.