Boost to Enhertu's prospects as FDA clears Roche diagnostic
HER2 staining
Just days after the FDA approved AstraZeneca and Daiichi Sankyo's Enhertu for a potentially lucrative new use, the regulatory has now cleared a diagnostic test that could help unlock the drug's growth.
Roche is the recipient of the new approval, getting the go-ahead from the US regulator for its PATHWAY HER2 (4B5) test to detect HER2-ultralow status in metastatic breast cancer patients, in addition to its existing use for assessing HER2-low status.
The FDA's expansion of the diagnostic's label comes after Enhertu (trastuzumab deruxtecan), an HER2-targeting antibody-drug conjugate (ADC), became the first drug in the HER2 class to be approved for HER2-ultralow patients – in other words, those with an immunohistochemistry (IHC) score of zero, with faint staining in 10% of tumour cells or less.
Roche said in a statement that the interpretation of HER2 status in breast cancer is "evolving," with the new HER2-low and ultralow classifications allowing a more nuanced assessment than the old, binary system of classing tumours as either HER2-positive or HER2-negative.
"One in eight women in the US will face invasive breast cancer in their lifetime," said Matt Sause, chief executive of Roche Diagnostics, who added that there is a rising incidence of metastatic breast cancer, particularly among younger populations, that "underscores the urgent need for new diagnostic options."
Sause added that the approval of the test for determining HER2-ultralow status "offers new hope to patients by providing a possible path to HER2-targeted treatment where none existed before, helping clinicians transform outcomes for many facing this challenging disease."
Enhertu's approval in HER2-ultralow metastatic breast cancer came on the back of the DESTINY-Breast06 trial, which also supported another new indication for the ADC as a second-line treatment for patients with HER2-low disease, moving it up the treatment pathway as an option after one or more failed endocrine therapies.
It was first approved in 2019 for patients with inoperable or metastatic HER2-positive breast cancer who have already failed on at least two other treatments and has grown strongly since then, fuelled by six other label extensions across breast, gastric, and lung cancer, as well as a tumour-agnostic indication for HER2-positive tumours.
Enhertu had worldwide sales of more than $2.7 billion in the first nine months of 2024, up from $1.8 billion in the same period of the prior year and, according to AZ, has the potential to reach peak revenues of $5 billion a year or more. The company has said that the approvals from the DESTINY-Breast06 study could make the drug an option for 90% or more of patients.
