By Dennis Thompson
WEDNESDAY, Dec. 9, 2015 (HealthDay News) -- A pair of drugs already on the market appear to reduce the recurrence of breast cancer in women who've already undergone treatment, two new clinical trials show.
The chemotherapy drug capecitabine (Afinitor) seems to reduce by nearly a third the risk of breast cancer recurrence if women receive the drug following surgery to remove their cancer, researchers were to report Wednesday at the 2015 San Antonio Breast Cancer Symposium.
In addition, an osteoporosis medication called denosumab appears to reduce recurrence risk by 18 percent in women who have HR-positive breast cancer, a second study reports.
Denosumab (Xgeva) is usually given to women undergoing breast cancer treatment because hormone therapy for their disease can make their bones brittle, explained lead researcher Dr. Michael Gnant, a professor of surgery at the Medical University of Vienna in Austria.
This new study suggests that denosumab might also hold breast cancer at bay, Gnant said.
For the capecitabine study, Japanese researchers enrolled 910 patients who had HER2-negative breast cancer that did not fully respond to chemotherapy prior to surgery.
Some have suspected that these patients have breast cancer that is somehow resistant to chemotherapy, and that chemo following surgery might not do them any good, said study author Dr. Masakazu Toi, a professor at Kyoto University Hospital in Japan and founder and senior director of the Japan Breast Cancer Research Group.
These patients underwent standard treatment for their breast cancer, and then were randomly assigned post-treatment to take either capecitabine or a placebo. Capecitabine is an oral chemotherapy drug that is now available in generic form, at a cost of about $3 per 300-milligram tablet, Toi said.
The 455 patients assigned capecitabine received eight cycles of therapy, each lasting 21 days. They took the drug twice a day for the first 14 days, followed by seven days with no treatment.
Two years later, the researchers found the patients assigned capecitabine had a 31 percent reduced risk of disease recurrence compared with those assigned the placebo. Disease-free survival was slightly more than 87 percent for those assigned capecitabine and 80.5 percent for those assigned placebo.
Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City, said, "It is exciting to see that some success is seen with capecitabine because it offers hope to women whose tumors persist" despite preoperative chemotherapy.
However, the drug did not appear to significantly impact overall survival, which at two years was just over 96 percent versus almost 94 percent.
The study was funded by a grant from Specified Nonprofit Corporation-Advanced Clinical Research Organization and other donors to the Japan Breast Cancer Research Group.
The denosumab study focused on women with HR-positive breast cancer. About seven out of 10 patients have HR-positive breast cancer, which means that growth of their cancer cells is stimulated by female sex hormones.
Nearly all postmenopausal women with early stage, HR-positive breast cancer are treated with drugs that stop the production of estrogen, Gnant said.
Because low estrogen can cause osteoporosis, the U.S. Food and Drug Administration has approved denosumab as a post-therapy treatment to protect the women's bone health, Gnant said. Denosumab is a monoclonal antibody that blocks the action of osteoclasts, which are cells that break down bone.
Previous studies have shown that denosumab reduces bone fractures by half in women following breast cancer treatment, but researchers suspected that the drug might also improve their chances of remaining cancer-free.
Researchers enrolled 3,425 postmenopausal patients with early stage, HR-positive breast cancer and randomly assigned 1,711 to 60 milligrams of injected denosumab once every six months. The rest received a placebo.
After an average follow-up of four years, patients assigned denosumab had an 18 percent reduced risk of disease recurring compared with those assigned placebo, researchers found. Amgen Inc., which makes denosumab, funded the study.
Denosumab is not cheap -- it costs about $1,650 per injection, according to The New York Times, though the price could vary depending on where the drug is obtained.
But there appeared to be no significant side effects between the treatment group and the placebo group, Gnant said.
Gnant said denosumab likely helps reduce the risk of breast cancer recurrence by keeping dormant tumor cells from becoming active. "It's not a direct anti-cancer effect, but it makes it more difficult for them to cause a relapse," he said.
Dr. Eleonora Teplinsky, a medical oncologist with North Shore-LIJ Cancer Institute at Lake Success, N.Y., said the results of both trials "are intriguing, but, ultimately, longer follow-up and mature data are needed and eagerly awaited.
"Additionally, it is important to recognize that there is no 'one size fits all' approach to breast cancer and subset analyses will be helpful in determining which patients may benefit most from these interventions," Teplinsky said.
Research presented at medical meetings is considered preliminary until published in a peer-reviewed journal.
For more on hormone therapy for breast cancer, visit the U.S. National Cancer Institute.