SAN FRANCISCO – Pembrolizumab immunotherapy with multi-site stereotactic body radiotherapy (SBRT) appears to be a safe and effective treatment in patients with advanced solid tumors, according to findings from a phase 1 study.
Of 79 patients with metastatic solid tumors who progressed on standard treatment and who were enrolled in the study, 68 underwent multi-site SBRT, received at least one cycle of pembrolizumab (Keytruda), and had imaging follow-up. The overall objective response rate in those 68 patients was 13.2%, Jeffrey Lemons, MD, reported at the ASCO-SITC Clinical Immuno-Oncology Symposium.
Dr. Jeffrey Lemons
When responses in the non-irradiated lesions (out-of-field responses) were measured based on a 30% reduction in any single lesion, the rate was 26.9%. But when defined by a 30% reduction in aggregate diameter of the non-irradiated measurable lesions, the rate was 13.5%, he said. While both approaches for measuring response are acceptable, Dr. Lemons noted, it’s important to be sure which one is being used in a given study.
Overall, 73 patients received both SBRT and pembrolizumab (5 had no imaging follow-up). They had a mean age of 62 years and a median of five prior therapies. Cancer types included ovarian/fallopian tube cancer (12.3%), non–small cell lung cancer (9.6%), breast cancer (8.2%), cholangiocarcinoma (8.2%), endometrial cancer (8.2%), colorectal cancer (6.8%), head and neck cancer (5.5%), and other tumors, each with less than 5% accrual (41.2%).
The number of sites treated with SBRT was two in 94.5% of patients, three in 4.1%, and four in 1.3%; 151 lesions in total were treated.
The premise for combining pembrolizumab and SBRT is that response to anti-programmed cell death-1 (PD1) therapy seems to correspond with interferon-gamma signaling, and that SBRT can stimulate innate and adaptive immunity to potentially augment immunotherapy, Dr. Lemons explained. In addition, anti-PD1 treatment outcomes are improved with lower disease burden.
Multi-site radiation is an emerging paradigm for eradicating metastatic disease, he said.
Patients included in the study had metastatic solid tumors and had progressed on standard treatment. They had measurable disease by RECIST, and metastases amenable to SBRT with 0.25 cc to 65 cc of viable tumor.
Tumors larger than 65 cc were partially targeted with radiotherapy. Radiation doses were adapted from recently completed and ongoing National Cancer Institute trials and ranged from 30-50 Gy (3-5 fractions) based on anatomic location.
Pembrolizumab was initiated within 7 days of the final SBRT treatment.
Dose-limiting toxicities, all grade 3, occurred in six patients during a median follow-up of 5.5 months, and included pneumonitis in three patients, hepatic failure in one patient, and colitis in two patients, but there were no radiation dose reductions, Dr. Lemons said.
“This is the first and largest prospective trial to determine the safety of this combination,” he explained. “There was some intriguing clinical activity ... and we feel that this justifies further randomized studies
The University of Chicago sponsored the study. Dr. Lemons reported having no disclosures.
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SOURCE: Lemons J et al., ASCO-SITC abstract #20.