Aromatase Inhibitors Seem Less Effective in Obese Women

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Aromatase inhibitors are hormonal therapy medicines used to treat hormone-receptor-positive breast cancer and help stop the cancer from coming back (recurrence) in postmenopausal women.

Aromatase inhibitors stop the production of estrogen in postmenopausal women. Aromatase inhibitors work by blocking the enzyme aromatase, which turns the hormone androgen into small amounts of estrogen in the body. This means that less estrogen is available to stimulate the growth of hormone-receptor-positive breast cancer cells.

The aromatase inhibitors are:

  • Arimidex (chemical name: anastrozole)
  • Aromasin (chemical name: exemestane)
  • Femara (chemical name: letrozole)

A small British study has found that while obese women diagnosed with early-stage, hormone-receptor-positive breast cancer who took Arimidex and Femara had lower estrogen levels than before they started treatment, their estrogen levels were still more than double those of women at a healthy weight.

The study was published online in the July 16, 2012 issue of the Journal of Clinical Oncology. Read the abstract of “Suppression of Plasma Estrogen Levels by Letrozole and Anastrozole Is Related to Body Mass Index in Patients With Breast Cancer.”

Earlier research has suggested that Arimidex is less effective than tamoxifen at reducing recurrence risk in obese women.

Tamoxifen is a type of hormonal therapy called a SERM (selective estrogen receptor modulator). SERMs work by sitting in the estrogen receptors in breast cells. If a SERM is in the estrogen receptor, there’s no room for estrogen and it can’t attach to the cell. If there’s no estrogen in the breast cell, the cell doesn’t receive estrogen’s signals to grow and multiply.

The researchers for this study wanted to know why Arimidex was less effective than tamoxifen at reducing recurrence risk in obese women. Is tamoxifen more effective in these women? Or are aromatase inhibitors less effective?

To try and answer the questions, the researchers looked at the records of 44 postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer. After surgery, some of the women got Arimidex for 3 months, followed by 3 months of Femara. The other women got the same medicines in the opposite order: 3 months of Femara followed by 3 months of Arimidex. Information on the women’s body mass index (BMI) and estrogen levels before and after treatment with each aromatase inhibitor was included in the records.

A BMI of 30 or higher is considered obese. A BMI of 18.5 to 24.9 is considered a healthy weight.

The researchers found that before starting on either aromatase inhibitor, women with a BMI of 30 to 35 had estrogen levels that were more than twice as high as women with a BMI of less than 25.

After 6 months of taking the aromatase inhibitors, the obese women’s estrogen levels were lower, but still more than twice as high as the estrogen levels of healthy-weight women.

Femara lowered estrogen levels more than Arimidex in all the women, no matter how much they weighed.

These results suggest that aromatase inhibitors don’t completely block the production of estrogen in obese postmenopausal women. More research needs to be done to figure out if a higher dose of an aromatase inhibitor will lead to better results or if tamoxifen may be a better option for these women.

If you’ve been diagnosed with early-stage, hormone-receptor-positive breast cancer and are a postmenopausal woman with a BMI higher than 30, you may want to ask your doctor about this study. Ask your doctor to explain how your personal risk of recurrence has been calculated, as well as why a specific hormonal therapy is recommended for you.

When you’re deciding on a hormonal therapy treatment plan after surgery, keep two things in mind:

  • Every woman responds differently to treatment. What works for you may not work for someone else.
  • Your treatment plan isn’t written in stone. You can always switch medicines if another treatment has more benefits and fewer side effects.

Together, you and your doctor can decide on a hormonal therapy plan that makes the most sense for you.

At the same time, it’s a good idea to do everything you can do to keep your risk of recurrence as low as it can be, including making exercise and eating healthy foods a part of your daily routine. It may be hard to make these kinds of changes if you’re struggling to recover from treatment. Some women say it helps to think of eating well and exercising as important parts of their treatment plan. You might want to talk to your doctor or a registered dietitian to develop a healthy eating plan designed specifically for you and your needs. Losing weight is hard to do. But it can be done with exercise and careful diet changes. Be nice to yourself; don’t punish yourself. Always tell your doctor about any new diet or exercise plans you’re using.

In the Breastcancer.org pages on Eating to Lose Weight After Treatment and Exercise, you can learn more about creating a delicious, healthy diet and exercise plan to reach and maintain a healthy weight.

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