Extending Aromatase Inhibitor Use Beyond 5 Years May Benefit Some Women

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After surgery, women diagnosed with hormone-receptor-positive breast cancer usually take hormonal therapy medicine to reduce the risk of the cancer coming back (recurrence). Hormonal therapy given after surgery is called adjuvant hormonal therapy.

Hormonal therapy medicines work in two ways:

  • by lowering the amount of estrogen in the body
  • by blocking the action of estrogen on breast cancer cells

There are several types of hormonal therapy medicines. Tamoxifen, a selective estrogen receptor modulator (SERM), is one of the most well-known. Tamoxifen can be used to treat both premenopausal and postmenopausal women. In the early 2000s, the aromatase inhibitors:

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

were shown to be more effective at reducing recurrence risk in postmenopausal women and are now used more often than tamoxifen to treat women who’ve gone through menopause. Aromatase inhibitors aren’t used to reduce recurrence risk in premenopausal women.

In 2012 and 2013, large studies found that 10 years of tamoxifen was better than 5 because it:

  • lowered the incidence of breast cancer coming back (recurrence)
  • reduced the number of deaths from breast cancer
  • improved overall survival

So researchers wanted to know if taking an aromatase inhibitor for 10 years would offer more benefits than taking one for 5 years.

In June 2016, results from the MA.17R trial found that taking Femara for 10 years instead of 5 reduced the risk of recurrence and also reduced the risk of a new breast cancer being diagnosed in the opposite breast (contralateral breast cancer) in postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer. Still, women who took 10 years of Femara also had more broken bones. They also were highly selected, meaning they were doing well on Femara and not having severe side effects.

Now, new results from another study also show that an additional 5 years of Femara offers some benefit, but only for very specific women.

The research was presented on Dec. 7, 2016 at the 2016 San Antonio Breast Cancer Symposium.

Read the abstract of “A randomized, double-blinded, placebo-controlled clinical trial of extended adjuvant endocrine therapy (tx) with letrozole (L) in postmenopausal women with hormone-receptor (+) breast cancer (BC) who have completed previous adjuvant tx with an aromatase inhibitor (AI): Results from NRG Oncology/NSABP B-42.”

In the B-42 study, 3,923 postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer who had taken 5 years of tamoxifen or an aromatase inhibitor were randomly assigned to one of two treatments for another 5 years:

  • 2.5 mg of Femara per day
  • a placebo pill (a pill that looked just like Femara, but contained no medicine) each day

Half the women were followed for more than 7 years and half were followed for fewer than 7 years.

The results showed that an additional 5 years of Femara reduced the risk of:

  • breast cancer recurrence
  • contralateral breast cancer
  • a new cancer somewhere else in the body (non-breast malignancy)

Still, these differences weren’t statistically significant. This means they could have been due to chance and not because of the difference in treatment.

Taking Femara for 5 more years also didn’t improve overall survival. Overall survival is how long a woman lives, whether or not the cancer comes back or grows.

But taking Femara for 5 more years did reduce the risk of distant recurrence -- the breast cancer coming back in a part of the body away from the breast -- by 28%. This difference was statistically significant, which means that it was likely because of the treatment and not just due to chance.

Like all hormonal therapy medicines, Femara can cause side effects, including bone thinning and weakening, a higher-than-average risk of broken bones, fatigue, bone and joint pain, and hot flashes.

In this study, there was no difference in the rates of broken bones between women who took 5 more years of Femara and women who took the placebo. Still, women who took Femara had a higher risk of blood clots after the first 2.5 years of treatment.

“The study showed that extended adjuvant therapy with an aromatase inhibitor results in a small but potentially important benefit,” said Terry Mamounas, M.D., M.P.H., medical director of the University of Florida Health Cancer Center and lead researcher of the study. “But on the other side, it may have some significant side effects. So we need to be very careful in terms of who we select for extended therapy. Women at high risk of recurrence because the cancers are node-positive or large, high-grade tumors -- the higher the risk of recurrence, the more benefit there will be from extended therapy.”

Mamounas also said that women younger than 60 also may get benefits from extended aromatase inhibitor therapy because they have a longer life expectancy. So the reduction in the risk of contralateral breast cancer and distant recurrence may mean that the benefits of 5 more years of Femara outweigh the risks for younger women more than older women.

On the other hand, women who have significant side effects during the first 5 years of hormonal therapy, as well as women who have osteoporosis or are at high risk for the condition, probably are not good candidates for 5 more years of Femara.

“Five more years of Femara will prevent some breast cancer recurrences,” said Brian Wojciechowski, M.D., medical oncologist and Breastcancer.org medical adviser. “After the first 5 years, I plan to offer an extra 5 if the patient is doing well on the drug and she feels the benefits are worth the risks.”

If you’ve been diagnosed with early-stage, hormone-receptor-positive breast cancer and are finishing up 5 years of an aromatase inhibitor, you may want to ask your doctor about this study and whether taking Femara for another 5 years (for a total of 10 years of an aromatase inhibitor) makes sense for you. Talk to your doctor about any side effects you’ve been having and whether the benefits of another 5 years of Femara outweigh the risks of side effects. Together, you can decide on a treatment plan that’s best for YOU.

Listen to a Breastcancer.org podcast with Dr. Terry Mamounas about his research on extending Femara therapy for 5 more years.



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