Objective   This study aims to analyze the relationship between the effect of induction chemotherapy and the timing of radiotherapy in limited-disease or limited-stage small-cell lung cancer (LSCLC).

  Methods   Data from 148 LSCLC patients who received induction chemotherapy and radiotherapy between January 2009 and December 2012 were retrospectively analyzed. The effect of two to three cycles of induction chemotherapy was evaluated according to the RECIST version 1.1, which includes complete response (CR), partial response (PR), stable disease, and progressive disease. CR and PR were used to calculate response rate. The patients were divided into early and late groups based on immediate radiotherapy after two to three cycles of induction chemotherapy. The survival rate was analyzed using the Kaplan-Meier method. Log-rank test and Cox regression model were used to evaluate the influencing factors of the survival rate.

  Results   The median overall survival (OS) and progression-free survival (PFS) were 22.8 and 13.0 months, respectively. The early and late radiotherapy groups exhibited OS of 34.0 and 18.0 months, respectively, and corresponding PFS of 16.8 and 10.9 months. In the subgroup analysis, for the patients who responded to the induction chemotherapy, the early and late radiotherapy groups showed median OS of 18.0 and 19.5 months, respectively, and corresponding PFS of 19.4 and 11.7 months. For the patients who had no response to the induction chemotherapy, the early and late radiotherapy groups exhibited median OS of 18.0 and 9.5 months, respectively, and corresponding PFS of 12.4 and 10.3 months.

  Conclusion   All LSCLC patients who received two to three cycles of induction chemotherapy should receive radiotherapy as soon as possible after chemotherapy, regardless of their response to the induction chemotherapy.