Abiraterone is a relatively new drug developed by Cougar Biotechnology that inhibits the action of enzymes known to be involved in the synthesis of estrogen, the primary sex hormone found in women. Breast cancer in women often responds to estrogen, so reducing circulating hormone levels is often a goal of therapy.
Estrogen and Breast Cancer
Breast tissue contains receptors for estrogen that when activated by the presence of the hormone signal cells in the breast to grow. Normal growth in response to changing levels of estrogen occurs as a natural consequence of the menstrual cycle, but in some cases this system can go badly awry leading to rapid, uncontrolled cell growth and consequently a hormone sensitive tumor.
Sources of Estrogen
In young women, estrogen is primarily synthesized in the ovaries. Although most of the hormone supply in the body is created in the ovaries, there are also sites outside the reproductive tract that can produce estrogen such as the liver, breasts, adrenal glands, and fat cells.
Hormonal Therapy for Breast Cancer
One goal of hormonal therapy in hormone sensitive breast cancer is to reduce the risk of cancer recurrence by decreasing circulating levels of estrogen. Although the ovaries of post-menopausal women no longer produce estrogen, a significant amount of estrogen is still synthesized elsewhere in the body. The current standard of care for these women is to reduce hormone levels by administering a class of drugs called aromatase inhibitors that interfere with an enzyme involved in the final stages of the synthesis of estrogen.
How Abiraterone Works
Like the aromatase inhibitors, abiraterone works by blocking the action of enzymes that are necessary for the synthesis of estrogen. Abiraterone, however, works on enzymes that act at a different point in the metabolic path. The difference in target enzymes between the aromatase inhibitors and abiraterone has the potential to provide alternate treatment strategies in hormone positive cancers, particularly in cases where standard treatment has failed.
Current Status
At this time, trials are underway in the United Kingdom investigating the use of abiraterone in late stage breast cancer that has not responded to standard treatments. The trials are still in a relatively early stage, and preliminary results have not yet been released.
