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A new drug has been approved for treatment of a newly designated subtype of HER2 breast cancer. Maskot/Getty Images
  • About 55 percent of people with breast cancer fall into a subtype known as HER2-low breast cancer.
  • Federal regulators have approved the use of the drug Enhertu to treat this newly designated subtype.
  • Experts say the targeted therapy provides another option for people with this type of breast cancer.

The Food and Drug Administration (FDA) has approved a targeted therapy for a newly defined subset of breast cancer.

The drug trastuzumab-deruxtecan, also known by the brand name Enhertu, will now be available for people included in the HER2-low breast cancer subtype.

HER2 is a protein known as “human epidermal growth factor receptor 2.” It promotes the growth of cancer cells.

When people are screened for HER2, they are given an immunohistochemical (IHC) score. A score of 3 is considered HER2 positive, but scores below 3 have been considered HER2 negative and sometimes in need of additional classification.

Now those scoring below 3 with cancers that can’t be removed and whose cancers have metastasized are eligible for Enhertu. Prior to the FDA approval for this targeted therapy, these patients would have received endocrine therapy or traditional chemotherapy.

Estimates show that at least 55 percent of people with breast cancer fall into this HER2-low breast cancer category, including some patients who have hormone receptor-positive breast cancer or triple-negative disease.

“This is immediately going to change how doctors treat women with metastatic breast cancer,” said Dr. Jack Jacoub, a medical oncologist and medical director of MemorialCare Cancer Institute at Orange Coast Medical Center in California.

The new targeted therapy is given via an intravenous infusion every three weeks.

“This is a drug that has a payload,” Jacoub told Healthline. “The antibody is packaged with a chemotherapy drug. The antibody engages with the receptor, then releases the payload.”

“This particular medicine is so-called targeted or some people call it smart chemotherapy,” said Dr. Parvin Peddi, a medical oncologist and director of Breast Medical Oncology for the Margie Petersen Breast Center at Providence Saint John’s Health Center and Associate Professor of Medical Oncology at Saint John’s Cancer Institute in California.

“It gets inside the cancer cells after binding to HER2 and only there does it release its chemotherapy payload and kills the cancer cells,” Peddi told Healthline.

She says the process can lead to fewer side effects than traditional chemotherapy.

“Less nausea, less fatigue, less effect on the normal white blood cell counts that a lot of times go down with chemotherapy. It affects them a little bit, but definitely less,” Peddi explained. “You still have some hair loss, but in some patients, it is not complete, definitely not to the point of chemotherapy. It is much better tolerated and it has much less in terms of side effects.”

“There’s a small chance it could hurt the lungs. It’s called pneumonitis and about 11 percent of patients could experience it,” Jacoub added. “All the HER2 drugs have the potential to lower the heart function. So it’s important for patients to have their heart tests done.”

“It requires careful monitoring… but it’s definitely going to be a good option and opens up a whole new field of medications for these patients that we thought wouldn’t benefit from it,” said Peddi.

The FDA approval was based on a clinical trial called DESTINY-Breast04.

It included 557 participants ages 28 to 81 years old with 24% being 65 or older. The participants were 48% white, 40% Asian, 2% Black, and nearly 4% Latino.

They all fell into the HER2 low cancer subtype with cancers that were not removable and had metastasized. They all had one or two previous lines of chemotherapy.

The researchers found that the participants on trastuzumab deruxtecan had significantly longer progression-free and overall survival than those on their physician’s choice of chemotherapy.

Overall survival was slightly more than 23 months for those on trastuzumab deruxtecan versus more than 16 months for those on chemotherapy chosen by their physician.

Peddi says this trial was meant to give options to people who have few.

“It is exciting, but it’s not a home run. That’s the thing to keep in mind” she said. “It’s exciting because we never knew we could use anti-HER2 drugs in people who are not categorized HER2 positive.”

“So that opens up some treatment that was completely off limits to those patients” she added. “But it’s still not a cure for these patients. It does better for them than everything else on the market, but there is still room for improvement.”

“There are ongoing studies,” she noted. “Some of them are testing this in earlier stages as well, even in patients who haven’t even had surgery to see if it would help them avoid chemotherapy.”