GU Symposium 2021: Adding Pembrolizumab to Radium-223 for Metastatic Castration-Resistant Prostate Cancer
Posted: Friday, March 5, 2021
According to Atish Dipankar Choudhury, MD, PhD, of the Dana-Farber Cancer Institute, Boston, and colleagues, there does not seem to be evidence of increased CD4- or CD8-positive T-cell infiltration in patients with castration-resistant prostate cancer and bone metastases who were treated with radium-223 plus the anti–PD-1 checkpoint inhibitor pembrolizumab. The phase II trial results were presented during the virtual edition of the 2021 Genitourinary (GU) Cancers Symposium (Abstract 98).
Patients were randomly assigned in a 2:1 ratio to receive radium-223 with (n = 29) or without (n = 13) pembrolizumab. Bone biopsies were performed at baseline and at 8 weeks. More than half of patients (62%) had evaluable paired bone biopsies. From baseline to week 8, the median fold change in the proportion of CD4-positive T cells to the total cell count was higher with pembrolizumab than without (0.90 vs. 0.40; P = .87); this also seemed to be true for CD8-positive cells (0.67 vs. 0.40, respectively; P = .77). Grade 3 treatment-related nonhematologic adverse events were reported in 10% and 0% of patients treated with and without pembrolizumab, respectively.
The median duration of radiographic progression-free survival was 6.7 months with pembrolizumab and 5.7 months without; the median durations of overall survival were 16.9 and 16.0 months, respectively. Three patients treated with pembrolizumab experienced a reduction in prostate-specific antigen levels of 50% or higher. The rate of symptomatic skeletal events was lower with pembrolizumab than without (38% vs. 54%); pathologic fractures were reported in 0% and 23% of patients, respectively.
“This study revealed that radium-223 plus pembrolizumab did not result in unexpected adverse events but did not lead to prolonged radiographic progression-free or overall survival compared with radium-223 alone to support this two-drug combination in a biomarker-unselected population in this setting,” the investigators concluded.
Disclosure: For full disclosures of the study authors, visit coi.asco.org.
