The mammalian target of rapamycin (mTOR) inhibitor everolimus given with the aromatase inhibitor exemestane markedly boosts progression-free survival (PFS) in post-menopausal women with advanced breast cancer compared with hormonal therapy alone, according to updated results of the phase III Breast Cancer Trials of Oral Everolimus (BOLERO)-2 study reported at the 34th Annual San Antonio Breast Cancer Symposium (SABCS).

An earlier analysis showed a significant PFS benefit when everolimus was added to exemestane.

Gabriel N. Hortobagyi, MD, with the University of Texas MD Anderson Cancer Center in Houston, Texas, and associates randomized 724 women in a 2:1 ratio to everolimus (10mg/d) plus exemestane (25 mg/d) or placebo plus exemestane (25 mg/d) until disease progression or unacceptable treatment toxicity.

Trial participants had hormone receptor-positive metastatic breast cancer and evidence of progressive disease during or following prior treatment with the hormonal therapies letrozole or anastrozole.

Results of an additional six months of follow-up after the initial analysis for an overall median duration of follow-up of 17.5 months demonstrated a PFS of 7.4 months in patients randomized to combination therapy versus 3.2 months in patients assigned to exemestane alone. The difference between the two groups was highly significant, Dr. Hortobagyi said.

Clinical benefit rates (defined as complete responses, partial responses, and stability exceeding 6 months) were 50.5% and 25.5% in the two groups, respectively.

The results with everolimus were favorable irrespective of the presence of visceral disease, prior use of chemotherapy, or the number of prior therapies.

Adverse effects including dyspnea, hyperglycemia, oral mucositis, and fatigue were more common with combination therapy but were readily managed.

Dr. Hortobagyi said:

“The findings may establish a new standard of care in advanced breast cancer. Historically, treatment has involved the sequential use of as many hormone therapies as possible, aimed at controlling metastatic disease for as long as possible.

The new findings show that “in this group of heavily pretreated patients, all of whom had progressed on prior endocrine therapy, the addition of everolimus significantly prolonged PFS and improved the response rate with only a slight increase in toxicity. “

The BOLERO-2 study was conducted at 189 sites in 24 countries.

Everolimus is currently approved for both the treatment of renal cancer and pancreatic neuro-endocrine tumors.

Written by Jill Stein
Jill Stein is a Paris-based freelance medical writer.