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CancerQuest > Introduction to Patient Information > An Introduction to Cancer Treatments > Introduction to Hormonal Cancer Treatments > Enzyme Inhibitors and Receptor Down-Regulators

Enzyme Inhibitors and Receptor Down-Regulators

Additional hormonal treatments have been developed which can act as alternatives to treatment with SERMs (tamoxifen/raloxifene) or be utilized if SERMs are ineffective. Tamoxifen and raloxifene are both designed to interfere with the action of estrogen once it has entered a target cell. There are several other points of attack that may be taken to prevent signalling via estrogen. The most direct approach is to prevent the production of the estrogen by blocking the enzyme that is responsible for its formation, aromatase.

A second approach is to remove the target of the estrogen (the estrogen receptor). Both of these approaches to therapy have been developed for the treatment of breast cancer. Because these hormone treatments block estrogen production or function, they can have negative side effects on pregnancy. Therefore, they are used to treat postmenopausal women.⁽¹⁾

Watch animations of the estrogen receptor and the action of the drug tamoxifen.

Aromatase Inhibitors
After menopause, women produce a consistent low level of estrogen that is derived from androgen precursors. These precursors are converted to estrogen through the actions of the enzyme aromatase. By blocking the action of this enzyme, aromatase inhibitors prevent the formation of estrogen. There are two types of aromatase inhibitors that have been approved as treatment for postmenopausal women with estrogen-receptor positive metastatic breast cancer: steroidal inhibitors such as exemestane (Aromasin®) and non-steriodal inhibitors that competitively bind to aromatase (anastrozole and letrozole).⁽¹⁾

Anastrozole
Exemestane
Letrozole

If these drugs prove to be as effective as tamoxifen in preventing cancer growth, they will be a valuable addition to the options for the treatment of estrogen responsive cancers. This is especially true because they do not apear to have the side effect of increasing the risk of endometrial cancer.⁽¹⁾

Estrogen Receptor Down-regulators
By decreasing the concentration of estrogen receptors and their activity, the effects of estrogen can be negated.

Fulvestrant

References for this page:

1. Bentram DJ. "Role of Antiestrogens and Aromatase Inhibitors in Breast Cancer Treatment." Current Opinion in Obstetrics and Gynecology (2002). 14: 5-12. [PUBMED]