The cancer drug Enhertu (trastuzumab deruxtecan, or T-DXd) given before breast cancer surgery showed activity in patients with a newly identified subtype of disease known as HER2-low breast cancer, according to a study presented at the recent San Antonio Breast Cancer Symposium, the largest annual conference on breast cancer.
Human growth receptor, abbreviated as HER2, is found on the surface of breast cancer cells. It’s presence in high or low amounts suggests how responsive the tumor will be to certain treatments. In the past, HER2 status was based upon a score, with a number 3 or above indicating HER2-positive disease, which is known to be more aggressive and difficult to treat. A score below 3 was categorized as HER2-negative disease.
More recently a new breast cancer subtype has been identified: HER2-low disease. This category includes tumors with a HER2 score of 1 to 2, and represents 45 to 60 percent of all breast cancers. A score of 0 now indicates HER2-negative disease.
Enhertu has already been approved by the U.S. Food and Drug Administration (FDA) for breast cancer in women with HER2-low breast cancer that has spread and who have received chemotherapy, or who have breast cancer that has come back within six months of completing chemotherapy after surgery.
The Enhertu study presented at the San Antonio meeting is the first report of using it neoadjuvantly, or before surgery, for patients with hormone receptor-positive, HER2-low breast cancer that has not spread, said Aditya Bardia, MD, MPH, an attending physician at Mass General Cancer Center and director of breast cancer research at Harvard Medical School in Boston, who spoke at a press conference during the Symposium.
As of the research cutoff date, 68 percent, or 17 out of 25 patients in the study, responded to Enhertu, while 58 percent, or 14 out of 24 patients, responded to Enhertu together with an endocrine therapy drug, Dr. Bardia said. The research is ongoing.
Bardia says the new study is important because patients with this category and stage of disease do not have good options. “Patients with high-risk hormone-receptor-positive, including HER2-low, localized breast cancer are often treated with neoadjuvant combination chemotherapy, but the response rate is low,” he says.
“Furthermore, chemotherapy can be associated with significant toxicity, including [damage to the bone marrow and heart and the] risk of leukemia. Thus, there is an unmet clinical needs for better therapies,” he said.