Twenty-four years ago, a drug called Herceptin changed how doctors treat breast cancer. Its approval in 1998 made it possible to target the aggressive breast tumors tied to a gene called HER2. Other drugs quickly followed Herceptin and, over the years since, have substantially improved survival for people with the disease.
A quarter of a century later, another shift in treatment could be on the horizon. At the American Society of Clinical Oncology meeting, AstraZeneca and Daiichi Sankyo are presenting results proving that, for the first time, a targeted medicine can help metastatic breast cancer patients whose tumors express only low levels of HER2.
Clinical trial data revealed at ASCO and published in The New England Journal of Medicine Sunday show the drug, Enhertu, halved the risk of cancer progression compared to chemotherapy and reduced the risk of death by 36%.
“This is really, really impressive,” said William Jacot, a study investigator and medical oncologist at the Montpellier Cancer Institute. “I was not expecting something near so good to be achievable with HER2 breast cancer.”
Halle Moore, another investigator and the director of breast medical oncology at the Cleveland Clinic’s Taussig Cancer Institute, said some patients achieved an even greater benefit. The survival numbers, she added, are “extremely meaningful.”
There are important caveats, however. Enhertu is associated with a type of lung scarring that can require stringent monitoring to detect and manage. In a few cases in the trial, this side effect led to death. The length of follow-up is also relatively short, so it’s unclear just how long benefits might endure. It’s unknown exactly what level of HER2 expression is required for Enhertu to work, or how helpful the drug might be for so-called triple-negative patients, who have particularly fast-moving disease.
Nonetheless, the results are expected to change breast cancer treatment, according to experts interviewed by BioPharma Dive. HER2 expression has long been considered in binary terms, with a patient diagnosed as either “positive” or “negative.” Yet about half of metastatic breast cancer patients are somewhere in between, with tumors that have low, but still detectable levels of the protein. These patients don’t benefit from drugs like Herceptin and chemotherapy is the typical treatment for many.