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Exciting New Treatments for Fibroids:
Aromatase Inhibitors

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.

AI’s offer exciting potential to treat any hormone-dependent condition with laser-like precision and minimal side effects, including: image

  • breast cancer
  • fibroids
  • endometriosis

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.

image 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?
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{ 13 comments… add one }

  • Maxine August 3, 2009, 7:51 am

    I am very interested in Aromatase Inhibitors as a treatment for my fibroids. I have already had a multiple myomectomy (in 2004), where not all my fibroids were removed (the surgeon was concerned it would compromise my fertility and at the time, I was with a partner and we were trying for children). However, I am now 48 years old, but would still like to preserve my womb. Do you know where I could receive AI treatment? It does not appear to be something offered in the UK – if you have any information on how I could access this treatment, I would be most grateful if you could let me know. Also, could you tell me of any side-effects with this? Thanks again.

    Maxine McKenzie

  • Evelyn September 16, 2009, 2:16 pm

    I have 3 fibroids in my womb and need to know more about the Aromatase Inhivitors.

    • Shelley Binkley October 7, 2009, 7:38 am

      What questions do you have that I have not answered on this site? Please let me know.

  • georgia October 14, 2009, 10:24 am


    i live in southeastern north carolina and have a large (13cm) single fibroid and am interested in non-surgical methods to remove/shrink the fibroid such as the ones you mentioned above. can you please tell me where i might be able to get more information on these procedures. though i am located in the u.s., i would be willing to go out of the country.

    thank you,


    • Shelley Binkley October 20, 2009, 11:26 am

      As far as finding someone locally who can help you with this, I’d suggest the internet, the yellow pages, or you can contact The Americal College of Ob-Gyn to get a referral.

  • Frida October 23, 2010, 2:34 pm

    I live in Montreal, Canada.I have a large(12cm) fibroid and am interested in non-surgical methods to shrink the fibroid such as the 5mg misoprostal pill.Can you please tell me where I might be able to get a prescription for this medication. Though I am located in Canada.I would be willing to go to the U.S.A
    thank you

  • georgia October 25, 2010, 7:47 am

    dear frida:

    e-mail me and i will tell you about my experience with mifepristone, which involved traveling to spain.



  • Christina January 19, 2011, 9:46 am

    Hello Dr. Binkley,
    I have a problem with fibroids, also. In 2004, I had a myomectomy. I now have three fibroids, one of which is about 10-12cm. I had an ultrasound ablation, and that took care of many of the bulk issues, but the size bothers me. Bending over bothers me, many times even sitting can make me uncomfortable.

    I’d like to try Aromatase Inhibitors, but need to know exactly what side effects I can expect from them. Are they safe to take with other meds (I am beginning to take Elmiron)? supplements? Is 90 days the typical dosage period? How are AIs different from mifepristone, and do you prefer one over the other (excluding availability issues)? Finally, from the comments here, I’m assuming that people don’t think AIs are readily available. I’m thinking that I can just go to my Gyn and have her prescribe them to me. Is that correct?

    Thank you very much for your response.

    • Shelley Binkley April 4, 2011, 1:45 pm

      Side effects of AI’s are menopausal symptoms. I suggest you discuss the specifics of your situation with your own physician.

  • britt January 14, 2012, 4:58 pm

    i am a long time sufferer of endometriosis. i’m not sure if i have any fibroids. i am interested in AI’s and uterine ablation, and have been trying to figure out which route to go. i am 40 and done having children. i suffer from anemia and pretty much a constant period. the constant period is not normal, it is brown dead cell matter. it looks as if my uterus just sheds and sheds and sheds, and i’m perpetually bloated. i didn’t know which would be better, the AI’s or the ablation? any advice?

    • Shelley Binkley December 16, 2013, 7:17 am

      Hi Britt,

      Either one of these could be a good choice. If bleeding is the problem, ablation will probably be a quicker fix. I recommend you talk to your doctor.

      Thank you for reading the blog and sharing your experience.

      -Dr. B

  • susan July 2, 2012, 4:42 pm

    I have a very large fibroid and was wondering if I would be able to get this Al’s at Planned Parenthood?

    • Shelley Binkley December 15, 2013, 6:39 am

      Hi Susan,

      You would have to contact them directly for the answer to that question.
      Thank you for reading the blog and commenting.

      -Dr. B

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