ASCO 2016: 10 Years of Aromatase Inhibitor Therapy Reduces Breast Cancer Recurrence Without Compromising Quality of Life in Postmenopausal Patients

Key Points

  • Women in the extended letrozole group had a 34% lower risk of breast cancer recurrence.
  • The annual incidence of contralateral breast cancer was lower in the letrozole group than in the placebo group, and at 5 years of follow-up, 95% of women receiving letrozole and 91% of those receiving placebo were breast cancer–free.
  • Overall, there were no significant differences in either overall quality of life or menopause-specific quality of life between women who took letrozole for 5 years and those who received placebo.

For updated findings on aromatase inhibitor therapy from the 2016 San Antonio Breast Cancer Symposium, please click here, here, or here.

A randomized phase III clinical trial, MA.17R, found that postmenopausal women with early breast cancer benefit from extending aromatase inhibitor therapy with letrozole from 5 to 10 years. Following 5 years of an aromatase inhibitor and any duration of prior tamoxifen, women who received letrozole for 5 additional years had a 34% lower risk of recurrence than those who received placebo. The trial was led by the Canadian Cancer Trials Group with participation from the National Clinical Trials Network.

Data from two related abstracts from the MA.17R clinical trial were presented at the 2016 ASCO Annual Meeting, with the first by Goss et al reporting on safety and efficacy outcomes (Abstract LBA1) and the second by Lemieux et al reporting patient quality-of-life outcomes (Abstract LBA506).

“Women with early-stage hormone receptor–positive breast cancer face an indefinite risk of relapse,” said lead study author Paul Goss, MD, FRCP, PhD, Director of Breast Cancer Research at Massachusetts General Hospital and Professor of Medicine at Harvard Medical School. “The study provides direction for many patients and their doctors, confirming that prolonging aromatase inhibitor therapy can further reduce the risk of breast cancer recurrences. Longer aromatase inhibitor therapy also showed a substantial breast cancer preventative effect in the opposite, healthy breast.”

Overall survival was not significantly different in MA.17R between the two groups, but Dr. Goss noted that because of the slow chronic relapsing nature of hormone receptor–positive breast cancer, overall survival has proved difficult to demonstrate in clinical trials. Because of this, most endocrine therapies for breast cancer have gained regulatory approval based solely on improvements in disease-free survival.

Patient overall quality of life was comparable between the two groups. Small differences in physical role functioning in favor of placebo was observed, but these were not considered clinically significant. “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,” said Julie Lemieux, MD, lead author of the analysis of patient-reported outcomes from MA.17R and a researcher at the Centre hospitalier universitaire de Québec.

About the Study

The trial enrolled 1,918 postmenopausal women who had received 5 years of any one of three aromatase inhibitor therapies either as initial treatment or after any duration of prior tamoxifen. Although patients were allowed to enroll up to 2 years after completing previous aromatase inhibitor therapy, about 90% began receiving letrozole or placebo within 6 months of completing prior therapy.

Patient-reported quality of life was measured using the standard SF-36 questionnaire, which covers various areas of physical health and mental health, and a menopause-specific questionnaire, MENQOL. Of the 1,918 study participants, 1,428 were eligible to complete initial quality-of-life assessments. These were repeated at 12, 24, 36, 48, and 60 months, with more than 85% of women completing the questionnaires at follow-up.

Key Findings

Impact on Risk of Recurrence and New Breast Cancer (LBA1): Women in the extended letrozole group had a 34% lower risk of breast cancer recurrence. The annual incidence of contralateral breast cancer was lower in the letrozole group than in the placebo group (0.21% vs 0.49%), indicating a breast cancer prevention effect. At 5 years of follow-up, 95% of women receiving letrozole and 91% of those receiving placebo were breast cancer–free. The 5-year overall survival was 93% for women receiving placebo and 94% for those receiving letrozole (not statistically significant).

Quality-of-Life Findings (LBA506): Overall, there were no significant differences in either overall quality of life or menopause-specific quality of life between women who took letrozole for 5 years and those who received placebo. Small differences in physical role functioning were detected in favor of placebo, but these were less than that considered clinically meaningful.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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