Aromatase

Class

Aromatase inhibitor

Aromatase, also known as CYP19A1, is an enzyme responsible for the final step in estrogen biosynthesis: it converts androgens (testosterone and androstenedione) into estrogens (estradiol and estrone). This conversion occurs in several tissues, including ovarian cells in premenopausal women, and in fat, muscle, and breast tissue in postmenopausal women, where it becomes the primary source of circulating estrogen after the ovaries cease producing it directly. Many breast cancers depend on estrogen signaling through the estrogen receptor to drive tumor cell growth. By blocking aromatase, aromatase inhibitors reduce estrogen production throughout the body, depriving these hormone-sensitive tumors of a growth signal. This strategy is distinct from directly blocking the estrogen receptor, since it removes the hormone itself rather than its docking site, and the two approaches are sometimes used in different clinical settings or sequences. Aromatase inhibition is most relevant in postmenopausal women, because in premenopausal women the ovaries can compensate for reduced peripheral estrogen synthesis through feedback mechanisms that increase gonadotropin drive, so this class is generally paired with ovarian suppression when used earlier in life. The broader biological rationale rests on the well-established link between lifetime estrogen exposure and the growth of hormone receptor-positive breast tissue and tumors.