Endometriosis is a disease characterized by endometrial tissue (the tissue that lines the uterus) growing outside the uterus, forming lesions. Endometrial lesions may occur on the abdominal wall, the ovaries, the bowel, or the bladder. They swell and shed with the menstrual cycle just like the normal endometrium, but as they are located outside the uterus, cannot exit the body. This causes inflammation leading to pain and infertility.

While there is no cure for endometriosis, there are treatments that can help, including hormonal treatments. Aromatase inhibitors are a class of hormonal treatment used in combination with others to treat pain in endometriosis.

What are aromatase inhibitors?

Aromatase inhibitors are molecules that inhibit an enzyme called aromatase. Aromatase is present in the ovaries, and to a lesser extent in the skin and fat tissue. Its function is to produce estrogen. In endometriosis, estrogen regulates the hormone cycle that controls the swelling and shedding of endometrial lesions. In addition, endometrial lesions have a large amount of aromatase. This is thought to exacerbate the symptoms of endometriosis because aromatase provides additional estrogen to the endometrial lesions.

By blocking aromatase, aromatase inhibitors reduce the amount of estrogen being produced by the body and the endometrial lesions. With less estrogen present, the lesions do not grow or shed.

Aromatase inhibitors must be used with either a hormonal birth control or a gonadotropin-releasing hormone (GnRH) agonist in premenopausal women. Otherwise, ovarian cysts are likely to form following treatment with aromatase inhibitors.

Examples of aromatase inhibitors used to treat endometriosis

Aromatase inhibitors used to treat endometriosis include Femara (letrozole) and Arimidex (anastrozole).

Other information

The side effects of aromatase inhibitors are usually hot flashes and a reduced libido.

Women taking aromatase inhibitors should also be taking a calcium supplement, vitamin D, and a bisphosphonate to reduce bone loss (osteoporosis).

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