Aromatase Inhibitors [“AI’s”]* were originally developed to treat breast cancer. They block the conversion of estrogen-precursor molecules to estrogen in many types of cells (see picture). By blocking conversion of precursor molecules to estrogen, AI’s stop hormone-dependent tumors such as breast cancer and fibroids.
- breast cancer
Figure from Ian E. Smith, M.D., and Mitch Dowsett, Ph.D. Aromatase Inhibitors in Breast Cancer N Engl J Med 2003;348:2431-42.
Aromatase Gives Fibroid Tumor Cells a Megaphone
Fibroids are benign muscle tumors. They are the single leading cause of hysterectomy in the United States. Any advances we make in treating fibroids reduces the need for hysterectomy; and reducing the need for hysterectomy benefits all women and is a prime example of sustainable health care.
A fibroid develops when a muscle cell in the uterus “goes wild” and duplicates itself to form a ball of identical muscle cells. They usually range in size from 1-3 cm but can get as large as a half-term pregnancy.
Fibroid tumor cells contain abnormally high levels of the enzyme, aromatase, which converts estrogen pre-molecules to estrogen. This causes any estrogen present to stimulate growth of fibroids tumor cells.
Because fibroid tumors contain excess aromatase, normal or even low levels of estrogen circulating in the blood stream will be magnified in fibroid cells, causing them go grow. The normal non-fibroid uterus is the size of a kiwi fruit; a fibroid uterus can approach grape-fruit-sized or larger.
Aromatase Inhibitors Shrink Fibroids with Few Side Effects
Anastrazole, given at 1 mg daily for 90 days, shrinks fibroids by 55%. It reduces pressure symptoms from fibroids and increases the blood count in people who are anemic by reducing menstrual blood loss (due to decreased fibroid volume).
From Varelas et al. Effect of Anastrazole on Symptomatic Leiomyomata, Obstet Gynecol 2007;110:643–9
Since AI’s acts within cells, rather than by an mechanism outside the cells, they have few side effects. AI’s are not estrogens or progesterones but they impact the effects circulating hormones have on tissues they act upon.
Aromatase Inhibitors Can Be Used Alone or Combined with Other Modalities to Most Effectively Treat Fibroids
AI’s can be combined with other treatment modalities to reduce the need for hysterectomy. For example, in a woman with heavy bleeding, anemia, and a 4 cm fibroid (2 inches) endometrial ablation can be used in the near-term to reduce life-threatening bleeding, while awaiting the aromatase inhibitors to do their job and shrink fibroids.
Smith, IE and Dowsett, M. Aromatase Inhibitors in Breast Cancer, N Engl J Med 2003;348:2431-42.
Varelas et al.Effect of Anastrazole on Symptomatic Leiomyomata, Obstet Gynecol 2007;110:643–9
Snarky Aside: AI’s were adopted into main-stream breast cancer treatment in the early 2000’s. The above article on anastrazole dealt with a study period of 3 months and was published 1.5 years ago; it is one of few that turn up in a Med-line search of aromatase and fibroids. Given how long they’ve been around—at least 5 years–why aren’t there tons of articles on AI’s for treatment of fibroids?
- Do you have fibroids?
- How have they impacted your life?
- What treatments have you tried?
- What would your ideal treatment for fibroids consist of?