2009P - CNS efficacy of immune checkpoint inhibitors when combined to stereotactic radiosurgery in extensive stage small cell lung cancer

Background

Brain metastasis is highly prevalent in Extensive Stage Small Cell Lung Cancer (ES-SCLC) and carries a poorer prognosis. Combined chemotherapy (CTX) and Immune checkpoint Inhibitor (ICI) is the current standard of care in treatment of ES-SCLC. Stereotactic Radiosurgery (SRS) either as whole brain radiation or Gamma knife radiosurgery is often employed to treat CNS disease. We aim to investigate the CNS benefit of ICI when combined with CTX in patients with ES-SCLC who received SRS.

Methods

Baseline characteristics, treatment and survival details were collected. Patients with baseline CNS disease who received SRS and at least one cycle of systemic therapy were included. Primary outcome of CNS progression free survival (CNS-PFS) was calculated using standard Kaplan-Meier methods, and Cox proportional hazard model were used to evaluate the association between survival outcome and treatment group while adjusting for age and baseline ECOG. Analyses were performed in SAS v9.4 (Cary, NC) at a significant level of 0.05. The CTX and CTX+ICI groups were labeled as cohort A and cohort B respectively.

Results

A total of 165 patients were included in the analysis. Cohort A had 122 patients (73.9%), while cohort B had 43 patients (26.1%). The baseline characteristics between the two cohorts were balanced as seen in table. The Cox proportional hazards analysis revealed a 30% benefit in CNS-PFS in cohort B when compared to cohort A (HR=0.7 CI=0.47-1.03). Additionally, there was a trend towards benefit in overall survival (OS) in cohort B (HR=0.74 CI=0.46-1.2).

Table: 2009P

Baseline characteristics

Conclusions

Although the CNS-PFS and OS trends did not reach statistical significance, due to the small number of patients, our study suggests a clear trend towards CNS-PFS and OS benefit when combining ICI+CTX to SRS. Thus, supporting the hypothesis of immune modulatory effect of SRS on the brain metastases tumor micro-environment. Larger studies are needed to confirm these findings.

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.