Extending Aromatase Inhibitor Treatment for 5 More Years No Better Than 2 More Years

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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. The aromatase inhibitors:

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

have been shown to be more effective at reducing recurrence risk in postmenopausal women and are used more often than tamoxifen to treat women who’ve gone through menopause. Aromatase inhibitors aren’t commonly 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 have been studying whether taking an aromatase inhibitor for an additional 5 years would offer additional benefits.

A study has found that taking Arimidex for an extra 5 years -- for a total of 10 years of hormonal therapy -- offers no more benefits than taking Arimidex for an extra 2 years -- for a total of 7 years of hormonal therapy.

The research was presented on Dec. 7, 2017 at the 2017 San Antonio Breast Cancer Symposium. Read the abstract of “A prospective randomized multi-center phase-III trial of additional 2 versus additional 5 years of anastrozole after initial 5 years of adjuvant endocrine therapy -- results from 3,484 postmenopausal women in the ABCSG-16 trial.”

The Austrian study included 3,469 postmenopausal women who had been diagnosed with stage I to stage III (early-stage) hormone-receptor-positive breast cancer and had taken 5 years of hormonal therapy between 2004 and 2010. The first 5 years of hormonal therapy were either tamoxifen, an aromatase inhibitor, or tamoxifen then an aromatase inhibitor.

(Note: The title of the abstract says that 3,484 women were in the the study, which is true, but information from only 3,469 women was able to be included in the final analysis.)

The characteristics of the women:

  • half the women were older than 64 and half were younger
  • 72% of the women were diagnosed with cancers smaller than 2 cm
  • 66% of the women had no cancer in their lymph nodes
  • 77% of the women were diagnosed with cancers that were both estrogen-receptor-positive and progesterone-receptor-positive
  • 80% of the women had lumpectomy to remove the cancer
  • 29% of the women had received chemotherapy before breast cancer surgery
  • 51% of the women had been treated with 5 years of tamoxifen
  • 49% of the women had been treated with other 5-year hormonal therapy regimens that contained an aromatase inhibitor

The women were randomly assigned to receive one of two extended hormonal therapy treatments:

  • 2 more years of Arimidex for a total of 7 years of hormonal therapy (1,731)
  • 5 more years of Arimidex for a total of 10 years of hormonal therapy (1,738)

The researchers wanted to see if disease-free survival and overall survival were better in one group than the other. Disease-free survival is how long the women lived without the cancer coming back. Overall survival is how long the women lived, with or without the cancer coming back.

After nearly 9 years of follow-up, there was essentially no difference in either type of survival between the two groups. Disease-free survival rates were:

  • 71.1% for women treated with an additional 2 years of Arimidex
  • 70.3% for women treated with an additional 5 years of Arimidex

Overall survival rates were:

  • 85.4% for women treated with an additional 2 years of Arimidex
  • 84.9% for women treated with an additional 5 years of Arimidex

The only difference that the researchers saw between the two groups was that women who took an additional 5 years of Arimidex had a slight increase in rates of broken bones compared to women taking Arimidex for an additional 2 years.

"After 5 years of standard endocrine therapy, 2 additional years of anastrozole are sufficient," said Michael Gnant, director and chairperson of the department of surgery at the Comprehensive Cancer Center at the Medical University of Vienna, who presented the research. "There is no benefit to continuing/escalating endocrine treatment beyond 7 years. I believe that these trial results should be implemented into daily practice at once. There is simply no rationale to keep most patients on extended AI for longer than two years. This result can help save a lot of unnecessary side effects for many women around the world."

If you’re a postmenopausal woman who’s been diagnosed with early-stage, hormone-receptor-positive breast cancer and are finishing up 5 years of hormonal therapy, you may want to ask your doctor about this study and whether taking Arimidex for another two years makes sense for you. Talk to your doctor about any side effects you’ve been having and whether the benefits of another 2 years of Arimidex outweigh the risk of side effects. Together, you can decide on a treatment plan that’s best for you.


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