Keytruda Shows Promise for Some with Highly Advanced Prostate Cancer in Phase 2 Trial

Keytruda Shows Promise for Some with Highly Advanced Prostate Cancer in Phase 2 Trial
The immunotherapy Keytruda (pembrolizumab) extended for at least two years the lives of a small proportion of men with metastatic castration-resistant prostate cancer (mCRPC) who had exhausted all other treatment options, data from a Phase 2 trial show. While no association was seen between PD-L1 status and treatment responses, some of the men carried mutations in genes involved in DNA repair. These mutations will now be evaluated as potential predictive biomarkers to identify patients who are more likely to benefit from Keytruda. The study, “Pembrolizumab for Treatment-Refractory Metastatic Castration-Resistant Prostate Cancer: Multicohort, Open-Label Phase II KEYNOTE-199 Study,” was published in the Journal of Clinical Oncology. Keytruda, an immune checkpoint inhibitor marketed by Merck (known as MSD outside the U.S. and Canada), suppresses a mechanism often used by cancer cells to evade anti-tumor immune responses. By preventing the interaction between the PD-1 receptor in immune T-cells and its ligand PD-L1 in cancer cells, Keytruda boosts T-cells’ ability to detect and fight tumor cells. Because it targets the PD-1/PD-L1 interaction, patients with higher levels of PD-L1 on their tumor often respond better to Keytruda and similar  immune checkpoint inhibitors. The international KEYNOTE-199 Phase 2 trial (NCT02787005) evaluated the safety and effectiveness of Keytruda in 258 mCRPC patients who had acquired resistance to docetaxel chemotherapy and androgen deprivation therapy (ADT). The study comprised three groups of patients. Group 1 had 133 men with PD-L1 positive tumors (meaning their tumors expressed PD-L1, the protein to which PD-1 on immune cells binds to), group 2 included 66 men with PD-L1 negative tumors, and group 3 had 5
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