Enzalutamide With Ribociclib in Treating Patients With Metastatic Castrate-Resistant, Chemotherapy Naive Prostate Cancer That Retains Retinoblastoma Expression

This phase Ib/II trial studies the safety, side effects, best dose, and effectiveness of ribociclib when given with enzalutamide in treating patients with castrate-resistant prostate cancer that has spread from the primary site (place where it started) to other places in the body (metastatic), is chemotherapy naive, and retains retinoblastoma expression. Testosterone can cause the growth of prostate cancer cells. Hormone therapy using enzalutamide may fight prostate cancer by blocking the use of testosterone by the tumor cells. Ribociclib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Enzalutamide with ribociclib may be safe, tolerable and/or effective in treating metastatic, castrate-resistant, chemotherapy naive prostate cancer that retains retinoblastoma expression.