Randomized phase I/II trial of pembrolizumab with and without radiotherapy for metastatic non-small cell lung cancer.

9104 Background: We present findings of a randomized phase I/II trial studying PD-1 blockade with and without radiotherapy to lung lesions in patients with metastatic NSCLC. Methods: Patients with metastatic NSCLC were randomized to receive pembrolizumab with or without lung-directed radiotherapy (RT). RT referred to stereotactic body radiation therapy (SBRT, 50 Gy in 4 fractions or 70 Gy in 10 fractions) or traditional fractionation (45 Gy in 15 fractions). Pembrolizumab (200mg IV) was started on day 1 and given every 3 weeks for up to sixteen cycles. The primary endpoint was out-of-field response rate (RR), which refers to complete (CR) or partial response (PR) per irRC criteria. Results: Of 124 enrolled patients, 103 received treatment, 5 withdrew consent, 15 screen failures, and 1 was not financially cleared. Twenty-one patients completed 16 cycles of pembrolizumab; 16 patients received SBRT and 20 received traditional RT. Seven patients received salvage RT after progression on pembrolizumab alone and 15 patients received RT six months before starting the trial. In the combined-modality arm, there were 2 grade 4 toxicities and 9 grade 3 toxicities related to treatment. In the pembrolizumab arm, there were zero grade 4 toxicities and five grade 3 toxicities. At the present time, 72 patients were evaluable for response, 36 in both arms; median follow-up was 15.4 months (range: 1.4-125.2 months). RR for out-of-field lesions was 22% and 25% for the pembrolizumab + RT vs pembrolizumab respectively (p = 1.00); median PFS was 10.9 months (95% CI, 8.1-15.3 months) and 8.4 months (95% CI, 3.9-17.1 months) respectively (p = 0.83). When comparing the SBRT vs traditional fractionation sub-cohorts, non-irradiated RR was 38% and 10% respectively (p = 0.10); median PFS was 21.1 and 6.8 months respectively (p = 0.03). Within the pembrolizumab arm, comparing patients who received prior RT vs those that did not, RR was 33% and 19% respectively (p = 0.26). Conclusions: RT, while safe, did not increase the out-of-field response rate in NSCLC patients treated with pembrolizumab. Exploratory analysis suggests responses may be enhanced by SBRT, but not traditional fractionation, which warrants further investigation. Clinical trial information: NCT02444741.