In an international Phase III randomized study known as BOLERO-2, everolimus combined with the hormonal therapy exemestane has dramatically improved progression-free survival for women with metastatic breast cancer.

Everolimus, an immunosuppressant agent first used to prevent rejection of organ transplants, also has antiangiogenic properties that prohibit a tumor from forming its own vascular system.

The 724 metastatic breast cancer patients enrolled in the trial were all post-menopausal, had hormone receptor-positive disease and evidence of progressive disease. The median age was 62. The study’s primary endpoint was progression-free survival.

In patients receiving the everolimus combination, researchers found a progression-free survival of 7.4 months, compared to 3.2 months in those who took exemestane alone, a finding described as “highly significant.”

The clinical benefit rate — complete responses, partial responses and stability exceeding six months — was 50.5% in those in the combination arm, compared to 25.5% in those who received hormone therapy alone.

“Over the years, our treatment approach for such women with metastatic breast cancer has been sequential use of as many hormone therapies as possible, keeping metastatic disease under control for as long as possible,” says Gabriel Hortobagyi, M.D., professor and chair of the Department of Breast Medical Oncology.

“These findings may allow us to change our approach. In this group of heavily pre-treated patients, all of whom progressed on prior endocrine therapy, the addition of everolimus resulted in significant prolongation of progression-free survival and an improved response rate with only modest toxicity.”

Reported in the Feb. 9, 2012, edition of the New England Journal of Medicine. 

Also reported in December 2011 at the 34th Annual Meeting of the Cancer Therapy and Research Center-American Association for Cancer Research San Antonio Breast Cancer Symposium.