The phase 2, single-center study was conducted in 62 patients with head and neck cancer and at least two metastatic lesions. They were randomly assigned to receive nivolumab with or without additional radiation, delivered as stereotactic body radiation therapy (SBRT), but directed at only one of the metastatic lesions.
The results showed a similar rate of tumor shrinkage and disappearance in both groups (34.5% for nivolumab vs. 29.0% for the combination; P = .86) reported Sean McBride, MD, MPH, Memorial Sloan Kettering Cancer Center, New York, and colleagues in a paper published online in the Journal of Clinical Oncology.
The finding indicates that there was no abscopal effect, the team concluded.
The abscopal (from the Latin ab “away from” and scopus “target”) effect, first described in the 1950s, is a hypothetical result of radiation, whereby tumors situated outside the radiation field are reduced or eliminated by an assumed reaction mediated by the immune system.
This study is only the second randomized controlled trial to look at this effect. A previous trial in lung cancer (JAMA Oncol. 2019;5:1276) also failed to show a significant difference in objective response rate, the primary outcome.
In both studies, there was also no improvement in progression-free survival (PFS) or overall survival (OS) with the addition of radiation.
“There are still die-hard proponents of the existence of an abscopal response, but it is clear from our data – there is no abscopal response,” lead study author Nancy Lee, MD, said in an interview.
Dr. Lee, also from Memorial Sloan Kettering, was referring to this trial in head and neck cancer specifically. But previous nonrandomized studies have also reported response rates for the combination of SBRT and immunotherapy that are similar to monotherapy, the authors point out. Overall, the collective data in oncology suggest that the abscopal response is “relatively rare,” the team comments.
A more emphatic statement comes from a pair of oncologists in an accompanying editorial.
The new study “provides the clearest evidence so far that the abscopal effect, contrary to widely held perception in the field, remains exceedingly rare,” wrote Tanguy Seiwert, MD, medical oncologist, and Ana Kiess, MD, PhD, radiation oncologist, both at Johns Hopkins University, Baltimore.
This is a “well-executed study that has broader implications beyond head and neck cancer and speaks to larger issues of combination therapies in the era of cancer immunotherapy,” they also wrote.
The practice of using limited SBRT on any tumor type – along with anti–PD-1/PD-L1 therapy – “should not be pursued for the sole purpose of induction of an abscopal effect until we have better data to support any benefit,” the editorialists added.
It’s time to put the abscopal effect to rest, suggested Dr. Lee.
“Instead of focusing on whether an abscopal response exists or not, as it clearly did not in our phase 2 study, our focus should shift to the broader picture. What is the optimal timing of PD-1 or PD-L1 therapy in relation to radiotherapy?” she said.
The answer appears to be sequentially – and not concurrently, which is how radiation has been used to induce the would-be abscopal effect, she explained. “I personally feel that immunotherapy should not be given concurrently with radiation therapy.”
Damning data for the concurrent approach come from the phase 3 Javelin Head and Neck 100 trial, she said. In March, trial sponsors announced that the trial was terminated as it was unlikely to meet its primary endpoint. Specifically, adding an anti–PD-L1 therapy to chemoradiotherapy was not superior to chemoradiotherapy alone.
On the other hand, in the phase 3 lung cancer study known as PACIFIC, chemoradiotherapy followed by sequential anti–PD-L1 therapy showed “dramatic” improvements in PFS and OS, the editorialists pointed out.