Long-Term AI Therapy Reduces Breast Cancer Recurrence

CHICAGO-Postmenopausal women with early breast cancer benefit from extending aromatase inhibitor (AI) therapy with letrozole from 5 to 10 years, and show no worsening of quality of life, according to a new study.

“This is the first study to show benefit of extending AI beyond 5 years, resulting in 34% reduction in recurrences,” said lead author Paul Goss, MD, PhD, director of breast cancer research at Massachusetts General Hospital and professor of medicine at Harvard Medical School in Boston, at the plenary session at the 2016 American Society of Clinical Oncology (ASCO) Annual Meeting, held June 3–7 (abstract LBA1).

“Women with early-stage hormone receptor–positive breast cancer face an indefinite risk of relapse. The study provides direction for many patients and their doctors, confirming that prolonging AI therapy can further reduce the risk of breast cancer recurrences,” said Goss.

Study results were published simultaneously in the New England Journal of Medicine.

The double-blind placebo-controlled trial (Canadian Cancer Trials Group MA.17R) enrolled 1,918 postmenopausal women who had received 5 years of AI therapy either as initial treatment or after any duration of prior tamoxifen. About 90% of patients began receiving letrozole or placebo within 6 months of completing prior therapy.

After more than 6 years follow-up, a total of 165 disease-free survival (DFS) events (67 on letrozole and 98 on placebo) occurred. There were 42 distant recurrences on letrozole and 53 on placebo, and 100 deaths in each arm.

The 5-year DFS was 95% for patients receiving letrozole vs 91% for those on placebo. The annual incidence of contralateral breast cancer was lower in the letrozole group (0.21%) vs the placebo group (0.49%), indicating a breast cancer prevention effect, Goss said.

The 5-year overall survival was 93% for women receiving placebo and 94% for those receiving letrozole, which was not statistically significant. He noted that most endocrine therapies for breast cancer have gained regulatory approval based solely on improvement of DFS.

“Unlike many anticancer therapies, AIs are readily accessible around the world, and therefore our results will further improve the outcome of many women with breast cancer,” said Goss.

In a separate study (abstract LBA506), patient-reported quality of life was measured using the standard SF-36 questionnaire 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.

At an ASCO press briefing, lead author Julie Lemieux, MD, a researcher at the Centre Hospitalier Affilié Universitaire de Québec in Canada, said 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. Differences in physical role functioning were detected in favor of placebo, but “this is very small and unlikely to be significant for women,” she said. “It is very reassuring for those women who want longer duration of adjuvant endocrine therapy that they can expect a persevered quality of life.”