As reported by Willemijn S.M.E. Theelen, MD, of the Netherlands Cancer Institute in Amsterdam and colleagues, the PEMBRO-RT study randomized 76 patients with stage IV NSCLC to pembro following SBRT to a single metastatic site (the experimental arm of the trial) or pembrolizumab alone. Pembrolizumab was given in a conventional dose and schedule in both arms of the trial and was administered within 7 days after SBRT on the experimental arm (JAMA Oncol. 2019 Jul 11. doi: 10.1001/jamaoncol.2019.1478).
The primary outcome was the overall response rate (ORR) at 12 weeks. Among patients on the experimental versus control arms, the ORR was 36% and 18%, respectively (P = .07). This did not meet the prespecified endpoint of improving ORR from 20% to 50% at 12 weeks. Additionally, although improved on the pembro plus SBRT arm of the trial, the median PFS and OS did not meet statistical criteria for improvement over the control arm, except among the 47 patients in the PD-L1 negative subset.
Dr. Alan P. Lyss
What this means in practice
There are a lot of potentially relevant variables in this small, randomized phase 2 study. As the authors discuss, if there is a dose and schedule of RT that facilitates antigen release and presentation and or an ideal latent period after radiotherapy that promotes an “abscopal effect” from I/O, it is unclear whether the ideal schema was used in the PEMBRO-RT trial.
At present, if a patient with stage IV NSCLC requires LAT for clinical reasons during I/O treatment, the patient can receive it safely, but without the expectation that the LAT will augment overall benefit from I/O. Additional preclinical work will need to help guide us about a rational way to design the next trial to test the concept of supra-additive benefit from these modalities. Not only is this combination “not ready for prime time” in clinical care, but it’s not ready for the large numbers of patients in a phase 3 clinical trial.
Dr. Lyss has been a community-based medical oncologist and clinical researcher for more than 35 years, practicing in St. Louis. His clinical and research interests are in the prevention, diagnosis, and treatment of breast and lung cancers and in expanding access to clinical trials to medically underserved populations.