Breast Cancer Drug Extends Survival Time By More Than Six Months in Trial

Breast cancers without amplification or over-expression of human epidermal growth factor receptor 2 (HER2) can still have low levels of HER2 that treatments could target. Though HER2-targeted treatments have not shown success in such patients in the past, a new drug trial has shown that could change.

The results of a drug trial for AstraZeneca and Daiichi Sankyo’s Enhertu, which has U.S. Food and Drug Administration approval to treat breast cancer patients with HER2-positive tumors, were presented at the American Society of Clinical Oncology Annual Meeting in early June. The findings show that the treatment expanded survival time by more than six months for metastatic breast cancer patients who were categorized as HER2-low, meaning they have few HER2 cells. Most had tumors that were hormone sensitive. The information was also published in The New England Journal of Medicine. The research team says the findings could open up treatment options for a substantial number of metastatic breast cancer patients.

Dr. Shanu Modi, the study’s lead investigator and medical oncologist at Memorial Sloan Kettering Cancer Center, says, “The results of [the trial] show for the first time that a HER2-directed therapy can provide a survival benefit to patients with low HER2 expression, indicating we must reconsider the way we categorize patients with metastatic breast cancer. The efficacy seen with Enhertu also reinforces the potential to establish a new standard of care for more than half of all patients with breast cancer currently categorized as having HER2-negative disease, but who actually have tumors with low HER2 expression.”

In this ongoing trial, 557 patients were split in a 2:1 ratio to either receive Enhertu or their doctor’s choice of chemotherapy. Of these patients, 494 had hormone receptor-positive disease, with the rest hormone receptor-negative. All had already received chemotherapy as a prior treatment. For the patients who were hormone receptor-positive, the median progression-free survival time was 10.1 months for those who had received Enhertu, compared with 5.4 months in those who had not. The first group also had a longer overall survival time, 23.9 months compared with 17.5 months.

Hormone-insensitive patients also benefitted, though. The Enhertu group’s median progression-free survival time was 6.6 months, compared with 2.9 months from the chemo group. They also lived an average of 6.3 months longer.

With all patients looped together, the median progression-free survival time was 9.9 months in the Enhertu group and 5.1 months in the doctor’s choice group. The survival time was also 23.4 months compared with 16.8 months, respectively.

Ken Takeshita, global head of research and development at Daiichi Sankyo, says, “As innovative research organizations, extending the survival for patients is one of our primary goals as we seek to identify potentially new treatment options for patients with metastatic breast cancer. These potentially practice-changing data show that [this trial] takes us one step closer to achieving this goal, as Enhertu is the first HER2-directed medicine to demonstrate a survival benefit in patients with HER2-low metastatic breast cancer.”

The team says their findings indicate that the way metastatic breast cancer patients are classified and treated may need to be reevaluated to give them a chance at potentially effective treatments.

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