ARN-509 is primarily used in the treatment of prostate cancer. It functions as an androgen receptor antagonist, effectively blocking the action of male hormones like testosterone that can fuel the growth of prostate cancer cells. This makes it particularly valuable in cases where the cancer is resistant to traditional hormone therapies. ARN-509 is often employed in advanced stages of the disease, including metastatic castration-resistant prostate cancer, to slow tumor progression and improve patient outcomes. Its targeted mechanism of action helps minimize side effects compared to broader hormonal treatments, offering a more precise approach to managing the condition. Clinical studies have shown its potential to extend survival and enhance the quality of life for patients with this challenging form of cancer.