HR+/HER- breast cancer is a common subtype of the disease in which cancer cells are responsive, initially, to hormone therapy, but not to drugs that target the HER2 protein. If it stops responding to initial treatments, and becomes metastatic (meaning it spreads) options are currently limited to chemotherapy. Sacituzumab govitecan (Trodelvy) is an antibody-drug conjugate. It combines an anti-cancer drug and an antibody that targets an antigen found in some forms of breast and bladder cancers. The FDA approved it for another difficult to treat cancer, metastatic triple-negative breast cancer, in 2020. In the phase 3 TROPiCS-02 trial, which is still underway, researchers compared the effectiveness of sacituzumab govitecan with current protocols for people with advanced HR+/HER2- metastatic breast cancer whose cancers had advanced despite earlier treatments. To be enrolled in the study, the 543 participants had to have already tried two to four lines of chemotherapy, as well as a hormone therapy and a category of drug known as CDK4/6 inhibitors. The highly anticipated findings pointed to improvements in progression-free survival (a period of time in which a cancer does not advance) over the course of a year in those in the sacituzumab govitecan group. At six months, for instance, 46 percent of those in the study on sacituzumab govitecan had not experienced disease progression, versus 30 percent for chemotherapy. At nine months, 33 percent of those in the sacituzumab govitecan group had not experienced progression, versus 17 percent at nine months. At one year, the numbers were 21 percent versus 7 percent. The drug resulted in complete or partial response or stable disease in 34 percent of those in the experimental group, and 22 percent of people receiving standard chemotherapy. This response lasted 7.5 months for the experimental medication versus 5.6 months for those on chemotherapy. The study’s lead researchers called the results so far “significant.” “To observe a clinically meaningful reduction in the risk of disease progression or death in these patients with limited treatment options is remarkable,” said Hope Rugo, MD, professor of medicine and director of breast oncology and clinical trials education at the University of California San Francisco Comprehensive Cancer Center. “Sacituzumab govitecan will be an important potential future treatment option for these patients," she said. If Gilead Sciences wins approval for treatment of HR+/HER2- patients, the drug will become the first antibody-drug conjugate approved for these patients.
