2000P - Efficacy and safety of thoracic radiotherapy after first-line immunotherapy in extensive stage small cell lung cancer: A multi-center retrospective study

Background

Immunotherapy combined with chemotherapy have become the standard first-line options in extensive stage small-cell lung cancer (ES-SCLC) in the past years. However, whether patients can benefit from consolidative thoracic radiotherapy (TRT) after first-line immunotherapy is still undetermined.

Methods

ES-SCLC patients who received standard first-line immunotherapy combined with chemotherapy with/without subsequent TRT were included from 3 cancer centers in China between February 2020 to December 2022. The clinical outcomes and safety were evaluated.

Results

220 ES-SCLC patients were eligible for our analysis, in which 136 received TRT and maintenance immunotherapy after chemotherapy, and 84 received maintenance immunotherapy only. TRT significantly improved the progression-free survival (PFS) (median 10.7 VS 8.5months, HR=0.662 [95% CI: 0.476-0.919], p=0.013), and decreased the intrathoracic lesion progression rate (13.23% VS 40.48%). Further analysis revealed that TRT with different biological effective dose (>60Gy or ≤60Gy), or different dose fractionation mode (conventional fractionation, hypofractionation or hyperfractionation) didn’t impact patient survival. However, addition of TRT in 3-6 weeks after chemotherapy generated significantly superior PFS compared with adding TRT after tumor progression on first-line treatment (median PFS 10.7m VS 8.3m, HR=0.414 [95% CI: 0.207-0.825], p=0.013). In addition, patients without liver metastases or with bone metastases were more likely to benefit from TRT (both p<0.05). TRT slightly increased ≥grade 3 adverse effect (30.88% VS 25%). Notably, the incidence of pneumonia was higher in the TRT group than in the maintenance immunotherapy group (19.9% VS 6%).

Conclusions

The addition of TRT after first-line immunotherapy improves PFS and local control in ES-SCLC patients. TRT should be preferential performed in 3-6 weeks after chemotherapy. Patients without liver metastases or with bone metastases benefit more from TRT. The application of TRT is generally safe excepted for increased pneumonia occurrence.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.