506P - Intrathoracic progression is still the most dominant failure pattern after first-line chemo-immunotherapy in extensive-stage small-cell lung cancer: Implications for thoracic radiotherapy

Background

This study aimed to compare the failure patterns before and after the introduction of immunotherapy and to determine the role of thoracic radiotherapy (TRT) in extensive-stage small-cell lung cancer (ES-SCLC) treatment.

Methods

We retrospectively reviewed 294 patients with ES-SCLC, of which 62.2% underwent chemotherapy alone, 13.3% underwent chemotherapy followed by consolidative TRT (TRT group), and 24.5% underwent chemotherapy with immune checkpoint inhibitor (ICI group). We performed propensity-score matching (PSM) to compare each treatment group.

Results

The median follow-up duration was 10.4 months. At the first relapse, in the cohort showing objective response, the proportion of cases showing intrathoracic progression was significantly lower in the TRT group (37.8%) than in the chemotherapy-alone (77.2%; P< 0.001) and the ICI (60.3%; P = 0.03) groups. Furthermore, in the subgroup analysis, TRT showed benefits related to intrathoracic progression-free survival (PFS) in comparison with ICI in patients with less than two involved extrathoracic sites (P = 0.008) or without liver metastasis (P = 0.02) or pleural metastasis (P = 0.005) at diagnosis. After PSM, the TRT group showed significantly better intrathoracic PFS than both chemotherapy-alone and ICI groups (P< 0.001 and P = 0.04, respectively), but showed no significant benefit in terms of PFS and OS in comparison with the ICI group (P = 0.17 and P = 0.31, respectively).

Conclusions

In ES-SCLC, intrathoracic progression was the most dominant failure pattern after immunotherapy. In the era of chemoimmunotherapy, consolidative TRT can still be considered a useful treatment strategy for locoregional control.

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.