The long-awaited results from a Phase III clinical trial have been released, indicating that ten years of hormone therapy reduces breast cancer recurrence without compromising quality of life. Researchers highlight the importance of these data, suggesting that they enable patients to make an informed decision on whether or not to extend adjuvant endocrine therapy following ER positive breast cancer.
The randomized trial, MA.17R, demonstrated that postmenopausal women with early breast cancer may benefit from extending aromatase inhibitor (AI) therapy with letrozole from 5 to 10 years. Led by the Canadian Cancer Trials Group with the National Clinical Trials Network, the study indicated that women who received letrozole for an additional 5 years after an initial 5 years of AI treatment, and any duration of prior tamoxifen, had a 34% lower risk of recurrence than those who received a placebo.
“Women with early-stage hormone-receptor positive breast cancer face an indefinite risk of relapse,” commented lead author Paul Goss (Harvard Medical School, Boston, MA, USA). “The study provides direction for many patients and their doctors, confirming that prolonging AI therapy can further reduce the risk of breast cancer recurrences. Longer AI therapy also showed a substantial breast cancer preventative effect in the opposite, healthy breast.”
While overall survival was not significantly different between the two groups, Goss suggests that hormone-receptor positive breast cancer has a slow relapsing nature, meaning that overall survival is challenging to demonstrate in a clinical trial. Additionally, the annual incidence of contralateral breast cancer was lower in the letrozole group than the placebo, indicating that extended treatment does have a preventative effect. After 5 years, 95% of the letrozole group were breast cancer free, compared with 91% of those receiving a placebo.
Importantly, there was no significant different in quality of life between the two groups, including menopause-specific quality of life. “A large proportion of women with early breast cancer are long-term survivors. As hormone therapy is given over a long period of time, measuring how women feel is very important,” explained Julie Lemieux (Centre Hospitalier Universitaire de Québec, Canada), lead author of the analysis of patient-reported outcomes from MA.17R.
Results from the clinical trial, which enrolled 1918 postmenopausal women, are being presented in the Plenary Session at ASCO16 (3–7 June 2016, Chicago, IL, USA).
“These data are important to the millions of women around the world with ER positive breast cancer, and suggest that longer durations of widely-available therapy reduce the risk of cancer recurrence, and prevent second cancers from arising,” said Harold Burstein, ASCO expert in breast cancer. “Ten years of any therapy is a long time. Fortunately, most women tolerate extended treatment reasonably well, with few side effects. Now, women can talk with their clinical team and make informed decisions to extend adjuvant endocrine therapy, or not.”