Among postmenopausal women with hormone-positive, early breast cancer, treatment with aromatase inhibitors (AIs) for 10 years significantly improves cancer-free survival, compared to the 5-year standard length of AI treatment. However, quality of life issues, bone density concerns, and a patient’s risk of a recurrence should be taken into consideration to determine the optimal length of treatment with AIs for each patient. These results were recently presented as a late-breaking abstract at the 2016 annual meeting of the American Society of Clinical Oncology (ASCO), as well as published in the New England Journal of Medicine.
The majority of breast cancers are considered hormone-positive (HR+), and are stimulated to grow from exposure to the female hormones estrogen and/or progesterone. Treatment for HR+-breast cancers include treatment to reduce the cancer cells’ exposure to these hormones. There are different types of treatment to reduce hormone exposure to HR+ breast cancer cells which have different mechanisms of action.
Aromatase inhibitors are commonly an integral component to treatment of HR+ breast cancers among postmenopausal women. These agents block the formation of estrogen in the body, thereby reducing the growth stimulus of HR+- breast cancers.
Standard therapy for HR+, early-stage breast cancer among postmenopausal women includes 5 years of AI therapy, 10 years of the antiestrogen tamoxifen, or 5 years of tamoxifen followed by 5 years of AI therapy. Researchers have speculated that treatment with AIs beyond the 5 years could prove to be beneficial; however, no long-term data until now has been published to provide definitive guidance on the optimal length of AI use for this patient population.
Long-term results from the MA.17R trial exploring the outcomes of extending AI therapy were recently presented at this year’s ASCO. The trial included nearly 2,000 postmenopausal women with HR+, early-stage breast cancer. Patients had already received approximately 5 years of AI treatment prior to participating in the trial. The majority of patients had also received tamoxifen prior to their 5 years of AI treatment before participating in the trial.
Following the patient’s prior treatment with AIs for 5 years, they were either treated for an additional 5 years of AI therapy with Femara® (letrozole), or they received 5 years of a placebo (inactive substitute).
- There were no differences in overall survival between the two groups of patients.
- Cancer-free survival at 5 years was 95% for patients treated with letrozole for the additional 5 years, compared with 91% for those who received placebo.
- The risk of a cancer recurrence in the opposite (contralateral) breast was increased by 58% among the group of patients who received placebo, versus those who were treated with letrozole for the additional 5 years. This translated into contralateral breast cancer recurrences occurring in 3.2% of patients who received placebo, compared with 1.4% of patients treated with the additional 5 years of letrozole.
- Quality of life measures were comparable between the two groups of patients; however, patients treated with the additional 5 years of letrozole had a lower bone mineral density and higher bone fracture rate than those who received placebo.
The authors of the trial stated that “Our study shows that it is safe and beneficial for postmenopausal patients with hormone-receptor–positive breast cancer to take an aromatase inhibitor as adjuvant therapy for 5 years after initial treatment.”
However, they also stated that “Ultimately, the decision of whether a patient should receive prolonged therapy with an aromatase inhibitor will depend largely on the extent of its effect on her in terms of toxic effects and quality of life, the extent to which bone mineral density is maintained, as indicated by sequential scans, and the patient’s individual risk of disease recurrence.”
Postmenopausal women who have been diagnosed with early-stage, HR+ breast cancer should speak with their physician regarding their individual risks and benefits of all different treatment options for their disease.
- Goss P, Ingle J, Pritchard K et al. A randomized trial (MA.17R) of extending adjuvant letrozole for 5 years after completing an initial 5 years of aromatase inhibitor therapy alone or preceded by tamoxifen in postmenopausal women with early-stage breast cancer. Proceedings from the 2016 annual ASCO meeting. LBA #1. Available at: http://meetinglibrary.asco.org/content/164642-176. Accessed June 6, 2016.
2.Goss P, Ingle J, Pritchard K, et al. Extending Aromatase-Inhibitor Adjuvant Therapy to 10 Years. New England Journal of Medicine. June 5, 2016. DOI: 10.1056/NEJMoa1604700.