Evista is approved to treat osteoporosis in postmenopausal women. It's a selective estrogen receptor modulator (SERM). SERMs protect bones in the same way as estrogen and have been shown to have antitumor activity in prostate cancer cells, write Ronald Shazer, MD, and colleagues.
Shazer works in Los Angeles at Cedars-Sinai Medical Center's Louis Warschaw Prostate Cancer Center.
"We undertook this study because we desperately need new therapies for patients with advanced prostate cancer," David Agus, MD, says in a news release. Agus is the research director at the Louis Warschaw Prostate Cancer Center and worked with Shazer on the Evista study.
Studying Mice, Men
Before testing Evista on prostate cancer patients, the researchers studied Evista in mice. Those tests showed that Evista slowed prostate tumor growth but didn't spur prostate cancer cells to die.
Next, Shazer's team studied 18 men with advanced prostate cancer. The men were nearly 73 years old, on average. They had androgen-independent prostate cancer.
Androgen-independent prostate cancer can grow without androgens, which are hormones (including testosterone) that produce masculine characteristics. Many early prostate cancers require androgens for growth, but advanced prostate cancers are often androgen-independent.
Androgen-independent prostate cancer "remains difficult to treat," write Shazer and colleagues. The men they studied had already tried treatments including surgery, chemotherapy, and hormone therapy.
All of the patients took 60 milligrams of Evista daily by mouth. They also got monthly checkups and took a blood thinner to avoid deep vein thrombosis, a type of blood clot. Blood clots are among Evista's possible side effects.
The researchers also measured the men's PSA (prostate specific antigen) levels. PSA is a protein whose levels tend to rise in the presence of prostate cancer, but high PSA levels don't always indicate prostate cancer.
About two months after starting Evista, prostate cancer had stabilized in five men (28%). One patient needed radiation due to uncontrolled bone pain, the study shows.
Twelve other men had a partial response to Evista. Their disease hadn't grown in size or spread, but their PSA levels were still rising.
PSA levels later rose in the five men whose prostate cancer had stabilized earlier in the experiment.
The researchers also note that Evista does not have any direct influence on PSA level.
Shazer's team says the patients tolerated Evista well. The researchers call for further tests of Evista in advanced prostate cancer.