CHICAGO — Daiichi Sankyo and AstraZeneca’s antibody-drug conjugate Enhertu gave HER2-low breast cancer patients a median of 5 more months without cancer progression or death compared to chemotherapy, according to data published Sunday at the American Society of Clinical Oncology’s annual meeting.
However, the treatment comes with more serious side effects compared to chemo.
In 2022, Enhertu won approval in patients with HER2-low breast cancer following chemotherapy, redefining how breast cancer patients are classified. HER2 is a protein that’s over-expressed in several cancers and is used to determine how to treat breast cancers.
In the past, patients have been stratified as HER2-positive or HER2-negative, and HER2-low patients would have been considered HER2-negative based on lab tests.
The companies may use the Phase 3 DESTINY-Breast06 study, which is set to be presented Sunday afternoon, to seek approval to move Enhertu into an earlier line of treatment and also a potentially larger population of HER2-low breast cancer patients.
The trial enrolled 866 patients with hormone receptor-positive breast cancer, the vast majority of whom had already tried hormone therapy. That included 713 patients who were considered HER2-low and 153 patients who were considered HER2 “ultra-low.” According to Daiichi CEO Ken Keller, nine of 10 breast cancer patients could be eligible for Enhertu based on these trial results.
In the study, the HER2 ultra-low patients saw similar efficacy from Enhertu compared to the HER2-low patients. Both HER2-low and ultra-low patients who received Enhertu did not die or see their cancers progress for a median of around 13 months, compared to about 8 months for those who received chemotherapy.
If Enhertu’s label is expanded, Sunday’s results will likely raise questions for oncologists as they discuss treatment options with their patients, MD Anderson Cancer Center breast oncologist Rachel Layman told Endpoints News. “The efficacy was better, but the toxicity was more, too,” she said.
Interstitial lung disease, or scarring of the lungs, is known to be a serious side effect of the treatment. In the clinical trial, three patients on Enhertu died from interstitial lung disease. All in all, 49 patients in the Enhertu arm experienced interstitial lung disease or pneumonitis, which is inflammation in the lungs, compared to just one in the chemotherapy arm.