Hormones are special chemicals that help in the regulation of body functions. They are produced in the glands and transported to their target sites via blood. Some hormones can affect the growth of cancer.
Hormonal therapy is a type of cancer treatment which can be used to stop or slow down cancer growth by addition, removal or inhibition of certain hormones. Hormone therapy is most commonly considered in the treatment of breast, prostate, thyroid and endometrial cancer. The medications used in the hormonal therapy fall into the following categories:
Adrenal Steroid Inhibitors
The adrenal glands, situated on top of each kidney, consist of two parts called the cortex and medulla. The cortex (or the outer part) handles secreting steroids (corticosteroids), which stimulate the production of other hormones; the inner portion of the adrenal gland is called the medulla. When adrenal steroid inhibitors (blocking agents) are given, it results in corticosteroids not being produced in the body; this action further stops production of hormones such as androgens, estrogen, glucocorticoids, and mineralocorticoids. As cancer cells are stimulated to grow by the effect of these hormones, any eventual decrease in these hormone levels cause the inhibition of cancer growth.
Androgens are the hormones that are present in both men and women, but they are usually the male sex hormones. These include testosterone and androsterone. These hormones are produced by the testes and adrenal cortex and stimulate the development of sexual and secondary characteristics in males. In women, these hormones are converted in the body through enzymatic reactions into estrogen – the hormone responsible for the development of female sexual and secondary characteristics. Androgens are used in the medical treatment of cancer as antagonists (agents that oppose or inhibit) to the activity of estrogen, thereby reducing the growth of estrogen-dependent cancers.The result achieved by such therapy is shrinking of the tumor. Androgens are used in the treatment of metastatic breast cancer in women by causing a drop in the estrogen level in the blood. Androgens are available as fluoxymesterone and methyltestosterone.
Antiandrogens (androgen antagonists) prevent the effects of testosterone, which handle the growth of some cancers (e.g. prostate cancer). It does this by blocking the receptors for testosterone, or by affecting its production in the body. By reducing the amount of testosterone using this treatment method, the cancer is not stimulated to grow and will consequently begin to shrink. Antiandrogens are used in combination with orchiectomy or GnRH analogs. Some Examples of antiandrogens include Flutamide, bicalutamide, and nilutamide.
Antiestrogens are the type of drugs given to prevent the actions of estrogen by blocking the receptors on cells that need estrogen to stimulate their growth. Certain types of breast cancers (estrogen receptor positive, ER+) depend on estrogen for their growth. Anti-estrogens compete to estrogen and bind with receptors in breast tissue, thereby inhibiting the effect of the estrogen. As a result, cancer cell growth is inhibited, which ultimately causes cancer cells to die and the tumor to shrink.
Aromatase is an enzyme that causes conversion of androgen into estrogen in both men and women. Aromatase Inhibitors (AIs) types of drugs given to stop androgens from converting into estrogen in the body. This is because in certain types of ovarian and breast cancers, in women, estrogen handles causing cancer to grow. Hence, by stopping the production of estrogen with AIs, we achieve the inhibition of cancer growth. They are primarily used in the postmenopausal women as ovarian estrogen production decreases. Aromatase inhibitors include Anastrozole, letrozole, etc.
Estrogens are female hormones that compete for androgen receptor sites and suppress the action of androgens (testosterone and androsterone). They work by promoting the development of female secondary sex characters. They are occasionally used in the treatment of certain prostate cancers by limiting the production of testosterone. Diethylstilbestrol (DES) is an artificial estrogen used primarily as a hormonal therapy for metastatic breast and prostate cancers, but it can lead to the formation of blood clots.
LHRH Agonists (Luteinizing Hormone-Releasing Hormone Agonists)
Hormones are naturally occurring substances produced in the body. They stimulate the targeted organ to perform some action. Agonists are substances similar to substances in the body, in that they produce the same action that the natural biological substances do. In other words, an LHRH agonist mimics the action of a substance produced in the body. LHRH agonists are mainly used in the treatment of prostate cancer. It is understood that prostate cancers are dependent on testosterone to grow, and by blocking the production of testosterone indirectly, testosterone-dependent tumors can be made to shrink. LHRH antagonists act by binding with receptors in the pituitary gland, thereby blocking the production of LH. LH is required for the stimulating production of testosterone in males and estrogen from the ovaries in females. In summary, LHRH agonists bind to receptors in the pituitary gland, stopping or reducing the production of estrogen and testosterone, and this in turn can cause an estrogen/testosterone-dependent tumor to shrink in size.
Selective Estrogen Receptor Modulators (SERMs)
The term ‘SERMs’ is used for this class of drugs because of their ‘selective’ ability to act on estrogen receptors. They only affect a subset of cells that respond to estrogen in a particular way, and not on all estrogen-receptive cells.
Raloxifene (Evista), Tamoxifen (Nolvadex), and Toremifene (Fareston) are examples of SERMs. Raloxifene, in particular, is used in postmenopausal women because it acts as an estrogen agonist by preventing bone loss and by lowering the amount of bad cholesterol in the blood. It also acts as an antagonist to estrogenic effects, such as those leading to breast and endometrial (uterine) cancer.
Gonadotropin-releasing Hormone (GnRH) Analogues
Gonadotropin-releasing hormone analogs are medications that stimulate the production of hormones called gonadotropins from the pituitary. Gonadotropins further stimulate the release of androgen and estrogen from tests and ovaries. GnRH analogs are used in the treatment of metastatic prostate cancer and metastatic breast cancer in premenopausal women. They initially increase then decrease the release of gonadotropins, androgens, and estrogens. GnRH analogs include Goserelin and Leuprolide.
Hormone therapy is an ideal treatment option for certain hormone-sensitive tumors that require hormones for their growth. In this particular treatment, medications are used that offer prevention to cancer cells from their growth hormones. Hormone therapy depends on factors such as age, tumor type and size, and the hormone receptors present on the tumor. Doctors and scientists are looking forward to exploring something new about the use hormone therapy in combination with other treatments.