A new osteoporosis drug hinders the growth of estrogen-sensitive cancer that has become resistant to treatment with tamoxifen, a study in mice shows. The results will be presented Saturday at The Endocrine Society's 95th Annual Meeting in San Francisco.
The medication, bazedoxifene, which is approved in Europe under the brand name Conbriza for the treatment and prevention of postmenopausal osteoporosis, also reduced estrogen activity and estrogen receptor levels in cultured human breast cancer cells, the study authors reported.
"Bazedoxifene, a known, safe drug approved in Europe, may present a near-term option as an effective therapy for breast cancer in patients who have relapsed during treatment with tamoxifen or aromatase inhibitors," said Suzanne Wardell, PhD, the study's principal investigator and a research scientist at Duke University, Durham, N.C.
About 70 percent of breast cancers are hormone sensitive, the National Cancer Institute estimates, meaning they need female hormones like estrogen to grow. In one-third to one-half of these patients, the cancer becomes resistant to medications that block either estrogen production or activity of the estrogen receptor, according to Wardell, who said, "These women then have few treatment options."
Treatment options include systemic, or whole-body, chemotherapy or often-painful injections of an anti-estrogen drug, fulvestrant into the buttocks muscle.
The investigators reasoned that one or more drugs known as selective estrogen receptor modulators, or SERMs, might prove effective in treating breast tumors that have developed resistance to hormone blockers. Most SERMs have anti-estrogen effects on some tissues and estrogen-like effects on other tissues. The new SERM bazedoxifene stimulates the estrogen receptor in bone to retain bone mineral density but inhibits estrogen receptor activation in the breast and uterus, Wardell said.
Wardell's team tested bazedoxi
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The Endocrine Society