ASP-9521 is primarily investigated for its potential application in the treatment of cancer, particularly prostate cancer. It functions as an androgen synthesis inhibitor, targeting the enzyme 17β-hydroxysteroid dehydrogenase type 5 (HSD17B5), which plays a crucial role in the production of androgens. By inhibiting this enzyme, ASP-9521 reduces the levels of active androgens, such as testosterone and dihydrotestosterone, which are known to drive the growth of androgen-dependent prostate cancer. This mechanism makes it a promising candidate for therapeutic use in patients with castration-resistant prostate cancer (CRPC), where traditional androgen deprivation therapies have become less effective. Clinical studies are ongoing to evaluate its efficacy, safety, and potential as part of combination therapies in oncology.