The US Food and Drug Administration (FDA) recently granted Novartis’ CDK4/6 inhibitor LEE011 (ribociclib), in combination with letrozole, Breakthrough Therapy designation for first-line treatment of patients with advanced or metastatic hormone receptor–positive, HER-2–negative breast cancer. Breakthrough Therapy designation accelerates drug development and is given to agents which demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development.

The Prostate Cancer Clinical Trials Consortium (PCCTC) is developing the promising new drug in metastatic castration-resistant prostate cancer (mCRPC). Its phase IB/II study led by Dr. W. Kevin Kelly of Thomas Jefferson University, a PCCTC clinical research site, is designed to evaluate the side effects and best dose of ribociclib when given with enzalutamide (Xtandi®) and to see how well they work compared to enzalutamide alone in treating patients with prostate cancer that does not respond to treatment with hormones (hormone resistant), has spread from the primary site (place where it started) to other places in the body (metastatic), is chemotherapy naïve, and retains retinoblastoma expression.

Notably, this study hypothesizes that the addition of ribociclib, which may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth, in combination with FDA-approved enzalutamide in patients with progressive mCRPC that retains RB expression will significantly enhance the efficacy of enzalutamide and further establish the efficacy of CDK4/6 inhibition in concert with androgen receptor (AR)-directed therapeutics as a potential intervention against tumors that retain RB expression. RB status, like HER-2 status in breast cancer, is believed to correlate with clinical response to targeted therapies like ribociclib.

In addition to Thomas Jefferson University the trial has also been activated at Memorial Sloan Kettering Cancer Center and the University of Michigan Comprehensive Cancer Center. It is expected to open at Roswell Park Cancer Institute in the coming weeks.

For more information including details on eligibility please visit the study’s ClincialTrials.gov page at https://clinicaltrials.gov/ct2/show/NCT02555189.