Researchers are constantly testing new medications for various conditions and breast cancer is no exception.
The first trial of endoxifen in humans found that the experimental medication endoxifen was safe, and showed early evidence that it may prevent tumor activity.
"Talk to your doctor to see if endoxifen could be right for you."
Matthew Goetz, MD, a Mayo Clinic oncologist, was lead author of this study.
Endoxifen is an active metabolite (a substance produced during metabolism) of tamoxifen, a hormonal therapy that has been used for over 40 years to prevent breast cancer and the risk of cancer recurrence (return).
In this Phase I trial (where researchers test a new medication in a small group for the first time to assess its safety and side effects), 22 women with estrogen-receptor positive breast cancer (breast cancer cells that grow with the help of the body's estrogen hormones) that was resistant to hormonal therapies like aromatase inhibitors and tamoxifen, were given endoxifen once a day orally on a 28-day cycle.
Some of these women had received chemotherapy, too (average of 2 women). Even at the highest dose of 160 milligrams a day, endoxifen appeared to be safe.
A small number of patients in the trial reported side effects including hot flashes, anemia and nausea.
“We achieved up to 60-fold higher levels of endoxifen compared to endoxifen levels achieved with the standard dose of tamoxifen," Dr. Goetz said in a press release.
"We have seen evidence for tumor regression in patients who had failed standard hormonal therapies including aromatase inhibitors, fulvestrant and tamoxifen. This is an exciting first step in the development of this drug," Dr. Goetz said.
The researchers are now working on finding the right dose of endoxifen for patients. According to the study, they plan to test doses of 20 mg a day and 100 mg a day.
The drug was co-developed by Mayo Clinic Cancer Center and the National Cancer Institute.
Study results were presented in December at the 2013 San Antonio Breast Cancer Symposium.
The study was funded by National Institutes of Health grants.