A new targeted treatment for breast cancer could reshape how doctors classify and treat the disease, offering another option for people whose tumors have spread or are unable to be removed through surgery.
On Friday, the Food and Drug Administration approved Enhertu, a medicine developed by AstraZeneca and Japanese drugmaker Daiichi Sankyo, for patients with advanced breast cancer that has low levels of a protein called HER2. It's the first targeted drug to be approved for this group of patients.
For more than two decades, HER2 status has shaped treatment of breast cancer. Named after the gene that encodes it, the protein’s presence in high levels is linked to more aggressive tumors that grow and spread faster. But the approval in 1998 of a HER2-targeting drug called Herceptin gave doctors a powerful treatment to combat breast cancers positive for the protein. Since then, several other drugs aimed at HER2 have joined Herceptin on the market.
Until now, HER2 status has been black or white — either positive or negative. However, testing showed Enhertu to be dramatically effective in treating tumors with very low levels of HER2, levels that would typically be considered negative.
The drug’s approval therefore creates a new classification on which doctors can act. About 60% of breast cancer patients who would previously be categorized as having HER2-negative tumors can be now be counted as HER2-low and potentially receive Enhertu, the FDA estimated. HER2-negative cancers are estimated to be by far the most common, accounting for between 80% to 85% of the more than 250,000 people who are diagnosed with breast cancer in the U.S. each year.
“Having therapies that are specially tailored to each patient’s cancer subtype is a priority to ensure access to safe and innovative treatments,” said Richard Pazdur, head of the FDA’s office that reviews cancer drugs, in a statement.
The FDA’s approval clears Enhertu for use in people with metastatic HER2-low breast cancer who have previously received chemotherapy, or those whose tumors returned during or within six months of completing chemo given alongside surgery.
Prior to Enhertu’s approval, these patients would otherwise receive hormone therapy or chemo.
The FDA reviewed Enhertu extraordinarily quickly, completing its assessment just 11 days after accepting AstraZeneca and Daiichi Sankyo’s approval application. However, the agency evaluated the drug under a program that allows for “real-time” review of clinical trial data as it’s generated, accelerating how fast regulators can reach a decision.
This real-time review was first used in 2019 but has become more common, featuring in the review of nine new cancer drugs last year.
AstraZeneca and Daiichi Sankyo tested Enhertu against chemo in a study of nearly 600 adults with metastatic or unresectable HER2-low breast cancer. Results, which were disclosed in June and published in The New England Journal of Medicine, showed treatment with Enhertu halved the risk of disease progression versus chemo, and lowered the risk of death by a third.
“It’s going to really significantly change our standard of care,” Nancy Lin, a medical oncologist at the Dana-Farber Cancer Institute, said in an interview with BioPharma Dive then. “In general, everyone who has metastatic disease is going to need to know their HER2 status,” and whether it’s defined as “positive, low, or zero.”
The drug can have difficult side effects and was associated with a type of lung scarring that led to the death of three patients in testing. Severe adverse reactions occurred more often in those who received chemo, however.