For Some Women With Breast Cancer, 10 Years of an Aromatase Inhibitor May Be Better Than 5

Taking the medicine longer prevented some recurrences and new breast cancers in postmenopausal women, but caused more side effects and didn’t prevent deaths
Breast Cancer News
July 7, 2016
Erin Rowley, Writer and Content Coordinator
Reviewed By: 
Pallav K. Mehta, MD

In a study published in June in the New England Journal of Medicineinfo-icon, researchers found a small but significant decrease in new breast cancers and breast cancer recurrences in women who took an aromatase inhibitorinfo-icon for 10 years instead of 5.

Background and Goals

Breast cancer that is hormone receptorinfo-icon-positive, which means it grows because of the hormones estrogeninfo-icon, progesteroneinfo-icon, or both, is the most common form of the disease. It is treated with hormonal therapyinfo-icon, which reduces those hormones in the body or changes the way the body responds to them.

Five years of daily treatment with a hormonal therapy medicine called an aromatase inhibitor is standard treatment for postmenopausalinfo-icon women with early-stageinfo-icon, hormone receptor-positive breast cancer. This can be given on its own or after up to 5 years of treatment with tamoxifeninfo-icon, another kind of hormonal therapy.

But some recent studies have shown up to 10 years of hormonal therapy is better than 5 years at preventing breast cancer recurrenceinfo-icon. In these studies, tamoxifen was used for all 10 years or up to 5 years followed by an aromatase inhibitor for up to another 5 years.

These researchers wanted to know if aromatase inhibitors would work better when given for 10 years instead of 5.


The trial involved 1,918 women with early-stage, hormoneinfo-icon-positive breast cancer who had already taken an aromatase inhibitor for 4.5-6 years. Most, but not all, of the women were also treated with tamoxifen in the past.

The women were randomly divided into two groups of 959. One group received 5 more years of daily letrozoleinfo-icon (Femarainfo-icon), an aromatase inhibitor. The other group received 5 years of a daily placeboinfo-icon.


 The study showed there had been no sign of new breast cancer or recurrence, called disease-free survival, after 5 years in

  • 95 percent of women in the letrozole group
  • 91 percent of women in the placebo group

After a medianinfo-icon 6.3 years, the number of deaths was the same: 100 in each group.

More bone-related side effects, such as pain and fractures, were seen in the letrozole group. But few women in either group stopped treatment because of side effects.

What This Means for You

These results show that taking an aromatase inhibitor for 10 years instead of 5 years may help women avoid some breast cancer recurrences and new breast cancers. But preventing those recurrences and new cancers did not prevent deaths in that group after a median 6.3 years. It’s possible a difference in deaths will be seen once more time goes by. But the current lack of difference in survival is something women with breast cancer, and their healthcare providers, need to consider as they think about whether 5 more years of treatment is worth more side effects and higher treatment costs. You may decide taking an aromatase inhibitor for an extra 5 years is the right decision, or you may decide that it isn’t. And that’s OK. Talk to your doctors about your unique risk factors, your priorities and how aromatase inhibitors affect your quality of lifeinfo-icon

The vast majority (more than 90 percent) of participants were still alive when these results were analyzed. This was true for women in the treatment group and in the placebo group. You may find it reassuring that whether you take hormonal therapy for 5 years, 10 years, or something in between, you are lowering your risk of breast cancer recurrence, new breast cancer and death from breast cancer.

For more information, read our Guide to Understanding Hormonal Therapy and our Guide to Understanding Treatment Decisions, and visit our page on hormonal therapy.

Goss, PE, Ingle, JN, Pritchard, KI, et al. Extending Aromatase-Inhibitor Adjuvant Therapy to 10 Years. The New England Journal of Medicine. Published online before print June 5, 2016; doi: 10.1056/NEJMoa1604700.

Additional Related Topics 
Hormone Receptor-Positive