Aug. 31 (UPI) -- A clinical trial of Z-endoxifen was found to be safe and effective at shrinking tumors in women with estrogen receptor positive metastatic breast cancer.
The drug Z-endoxifen is a potent derivative of the drug tamoxifen that can effectively treat estrogen receptor positive metastatic breast cancer, researchers at the Mayo Clinic show in a new study.
"Tamoxifen, is converted into endoxifen in the liver by an enzyme called CYP2D6. Our previous research found that tamoxifen may be less effective in women with poor CYP2D6 metabolism," Dr. Matthew Goetz, an oncologist at Mayo Clinic, said in a press release.
The study, published Aug. 30 in the Journal of Clinical Oncology, showed tumor shrinkage in women whose tumors progressed after standard anti-estrogen treatment, including tamoxifen.
"The primary goal of the study was to safely deliver therapeutic levels of endoxifen without the requirement for CYP2D6 liver metabolism," Goetz said. "However, one of the most surprising observations was the prolonged anticancer benefit, [which] in some cases lasted more than two years in women who had progressed on standard anti-estrogen therapies."
Researchers followed 41 women with estrogen positive metastatic breast cancer who had progressed on standard anti-estrogen treatment. They found that treatment with Z-endoxifen provided anti-tumor activity.
Z-endoxifen provided substantial drug exposure unaffected by CYP2D6 metabolism and acceptable toxicity.
"We are encouraged by these results and [are] hopeful that, based on these data and ongoing studies, Z-endoxifen could become a new U.S. Food and Drug Administration-approved treatment for women with estrogen positive metastatic breast cancer," Goetz said.