Breast cancer growth slowed by 14 months in new AstraZeneca drug study

London: AstraZeneca Plc and Daiichi Sankyo Co.’s Enhertu delayed the advance of a common type of breast cancer by more than a year in a large study, a result that may lead to expanded use of the medicine.

The treatment, already approved for several types of breast cancer, garnered sales of about $3.8 billion last year. It is routinely used as a second choice in roughly 20% of patients whose tumors have high levels of a protein called HER2. 

The study aimed to show the drug can be used for newly diagnosed patients with this type of cancer.

The drugmakers said they plan to speak to regulators, but doctors at the American Society of Clinical Oncology in Chicago said the decision won’t always be clear cut, in part due to the treatment’s side effects and a need for more data. 

In results reported at the meeting on Monday, patients who got Enhertu in combination with a standard medicine called pertuzumab lived for almost 41 months before their disease spread.

A group of volunteers who received a standard three-drug treatment, which includes pertuzumab, chemotherapy, and a third antibody drug called trastuzumab, lived for about 27 months before the cancer advanced. 

The tumours of 15% of patients who got Enhertu also shrank so dramatically they became undetectable on a scan. The comparison was 8.5% for the group on standard treatment.

“The bottom line is the data shows the regimen works. It is having a dramatic impact on long-term outcomes,” said Sara Tolaney, a breast oncologist at Dana-Farber Cancer Institute, who was lead investigator on the study. Based on the results, Enhertu should be offered as a potential initial treatment to patients whose tumors have high HER2 levels, she said.

But the new findings come with some caveats. In particular, doctors don’t yet know whether switching people to the new regimen upfront — as opposed to using Enhertu later when the disease progresses — will keep patients alive longer. That data is not in yet. 

Meanwhile, the Enhertu regimen has side effects including lung inflammation that can be serious. In the trial, 12% of the patients on Enhertu had lung inflammation. While it didn’t have major consequences in most cases, two patients died from the side effect.

The companies plan to discuss the results with regulators. 

“We think it is a very substantial clinical benefit paired with a favorable risk profile,” said Mark Rutstein, head of cancer development for Daiichi Sankyo. “With the data in hand we will speak to regulatory agencies.” The two companies collaborate on testing the drug, though AstraZeneca led this particular study.

For investors, the ASCO data will help determine just how big the ultimate market might be for Enhertu, Barclays’ Emily Field said in a note. The results could lead to a “potential paradigm shift” in the first-line treatment of this type of breast cancer, Field said. 

Doctors at the conference not involved in the study agreed that the results could put the drug in the conversation as a potential initial treatment, but how often it would be used was not clear.

Enhertu is an important drug, but the decision will not be straightforward, said Matthew Goetz, a Mayo Clinic oncologist. That’s because the regimen it would replace is well tolerated. Many patients on it can stop taking the chemotherapy after a few months and just continue with the other two drugs, which have fewer side effects, he said. 

By contrast, Enhertu comes with chemotherapy-like side effects including nausea and vomiting, he noted.

“A lot of investigators are not convinced they should give this drug to everybody until they progress, when in fact there are a lot of patients that can be treated with the old standard of care and do very very well,” Goetz said. “We need much more data to say everybody should be treated with this upfront.”

Nonetheless, the strong results in delaying progression “make it a clear front-runner” as an initial treatment for HER2 patients, said Jennifer Litton, a breast cancer oncologist at the MD Anderson Cancer Center in Houston.

Proving that using Enhertu upfront actually leads to longer survival “will be important because this drug does have some significant toxicity,” she said.