Most forms of breast cancer are promoted in their growth by the female sex hormone estrogen. Letrozole is used in postmenopausal women against hormone-dependent forms of breast cancer in order to reduce the growth rate of the tumor. It is also used as a cancer drug in patients who are in artificial menopause due to the removal of the ovaries.
The mode of action of letrozole:
In oestrogen-sensitive tumours, estrogen promotes cancer growth and the sowing of cancer cells in the rest of the body (metastases). With the withdrawal of estrogen, the growth of these special tumours, such as breast cancer, comes to a standstill. Some cancer drugs take advantage of this fact. These also include active substances from the aromatase inhibitor group such as letrozole. Like all aromatase inhibitors, the active substance blocks the aromatase enzyme, which is important for the formation of estrogen.
Before the menopause, the ovaries are the headquarters of estrogen production by aromatase. In the ovaries, however, aromatase inhibitors are ineffective and cannot suppress estrogen production. In addition, aromatase produces a small amount of estrogen in the liver, adrenal gland, fat tissue cells and - fatally - breast cancer cells. In these tissues, estrogen production continues even after the menopause. Now, however, it can be blocked by taking letrozole. Thus, the production of estrogen remaining after the menopause is also brought to a standstill.
In the medical field, the dosage of letrozole, an aromatase inhibitor, is 2.5 mg per day. However, various clinical studies have shown that 75% suppression of estrogen production can be achieved with doses of 0.1 to 0.5 mg.
Bodybuilders often use letrozole during the doping phase to counteract estrogenic side effects. The dosages are usually far below those in the medical field, so dosages of letrozole for the reduction of estrogen-related side effects of 0.25mg to 1.25mg are found every two days. Since the active substance letrozole has a half-life of more than two days (approx. 50 hours), taking it every other day is usually sufficient.