Apalutamide is used to treat certain types of prostate cancer (cancer in men that begins in the prostate [a male reproductive gland]) and has spread to other parts of the body or that has not spread to other parts of the body but has not been helped by other medical treatments. Apalutamide is in a class of medications called androgen receptor inhibitors. It works by blocking the effects of androgen (a male reproductive hormone) to stop the growth and spread of cancer cells.