Study: Extending aromatase inhibitor duration to 10 years lowers recurrence for ER/PR+ breast cancer patients

IN DEPTH REVIEW OF RESEARCH

Study background:

Researchers of this current study explored whether extending the length of time women took the aromatase inhibitor provided additional benefit. Paul Goss and his colleagues at Massachusetts General Hospital and other institutions presented their data on this new clinical trial (MA.17R) at the 2016 American Society of Clinical Oncology Meeting, Their observations of what happens when women take an aromatase inhibitor for 10 years instead of 5 were also published in The New England Journal of Medicine.

This study follows previous research showing that taking an aromatase inhibitor (Letrozole) after 5 years of tamoxifen improved disease-free survival.

Researchers of this study wanted to know:

Whether patients who stay on an aromatase inhibitor for 10 years have fewer recurrences and develop fewer new breast cancers than patients who take aromatase inhibitors for 5 years.

Population(s) looked at in the study:

The study enrolled 1,918 postmenopausal women who had estrogen receptor (ER)- and/or progesterone receptor (PR)-positive, early-stage breast cancer.

Women in the study fell into 1 of 3 groups:

• One group had received about 5 years of aromatase inhibitor (AI) therapy (Letrozole) in the researchers’ previous study, and took tamoxifen before AI therapy.
• The second group of women was not included in the previous study, and had received any of the 3 aromatase inhibitors currently in use for about 5 years, and took tamoxifen before AI therapy.
• The third group received about 5 years of any of the 3 current aromatase inhibitors currently in use, but never took tamoxifen.

Among the 3 groups of women, some were randomized to receive another 5 years of AI therapy (Letrozole) or 5 years of receiving a placebo.

Study findings: 

1. When the study ended, 95% of women who had 10 years of aromatase inhibitor therapy (Letrozole) had disease-free survival (meaning they did not develop a recurrence or a new cancer in the other breast), while 91% of women who had 5 years of aromatase inhibitor therapy had disease-free survival at the study endpoint.
   • In total, 67 patients who took Letrozole for 10 years developed a recurrence of cancer in the other breast, compared to 98 patients who took Letrozole for 5 years.
2. Women who took an aromatase inhibitor for 10 years had no additional benefit in overall survival compared to those who took an aromatase inhibitor for 5 years.
3. Patients who took Letrozole for 10 years were more likely to develop bone fractures than the patients who took it only for 5 years (14% versus 9%).

Limitations:

This research did not take genetic status into account, so how women with mutations in BRCA or other genes that increase cancer risk respond to an additional 5 years of aromatase inhibitor therapy is unknown. Some patients involved in the study had previously taken tamoxifen, while some had not. From the data presented, it is not known if the use of tamoxifen before an aromotase inhibitor affected a patient’s risk of recurrence or new cancer. Finally, a number of aromatase inhibitors are available, and not all women in the study took the same aromatase inhibitor for the first 5 years.

Conclusions:

The results of this study suggest that taking an aromatase inhibitor for 10 years instead of 5 may benefit ER- and/or PR-positive breast cancer patients. But there was no increase in overall survival between women who took aromatase inhibitors for 5 years and those who took aromatase inhibitors for 10 years. Patients should discuss with their health care provider all the risks and benefits when thinking about extending their aromatase inhibitor for longer than 5 years.

Posted 7/26/16

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