A synthetic steroidal substance with antineoplastic activity. Atamestane binds irreversibly to and inhibits the enzyme aromatase, thereby blocking the conversion of cholesterol to pregnenolone and the peripheral aromatization of androgenic precursors into estrogens. or A substance being studied in the treatment of some types of cancer. AT7519M blocks enzymes needed for cells to divide. It is a type of cyclin-dependent kinase inhibitor. Also called CDK inhibitor AT7519M.