A combination of trastuzumab deruxtecan (Enhertu) and pertuzumab (Perjeta) has been shown to reduce the risk of disease progression or death by 44 percent compared to the current standard treatment for people newly diagnosed with HER2-positive metastatic (advanced) breast cancer, according to a recent phase 3 trial.

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The results have “the potential to establish a new first-line standard of care for HER2-positive metastatic breast cancer, a setting which hasn’t seen significant innovation in more than a decade,” said Dr. Sara Tolaney, the lead study author.

What Are Enhertu and Perjeta — and How Do They Work?

Trastuzumab deruxtecan is an antibody-drug conjugate (ADC) approved by the U.S. Food and Drug Administration (FDA) in 2019. It’s designed to target HER2, a protein found in high amounts on some breast cancer cells. Once attached, the drug delivers chemotherapy directly into the cancer cell, helping limit damage to healthy tissue.

Approved in 2012, pertuzumab is a monoclonal antibody that also targets HER2, but in a different way. By blocking HER2’s ability to send growth signals, this drug helps slow or stop tumor growth.

Together, these medicines are designed to attack the cancer from two angles — by disrupting signals that drive tumor growth and delivering a powerful chemotherapy directly where it’s most needed.

What the Study Found

The trial included 1,157 people with locally advanced or metastatic HER2-positive breast cancer who hadn’t received earlier treatment for metastatic disease. Researchers compared outcomes between those who took trastuzumab deruxtecan plus pertuzumab and those who took the standard regimen called THP, a combination of taxane, trastuzumab (Herceptin), and pertuzumab.

After about two and a half years, people who got trastuzumab deruxtecan and pertuzumab had better results than those who took THP. Highlights include the following:

• They had a 44 percent lower chance of their cancer getting worse or of dying, compared to people who took THP.
• Their cancer did not progress for about 40.7 months, compared to 26.9 months for participants on THP.
• Tumors shrank in about 85 percent and went away completely for 15 percent — nearly double the 8.5 percent rate of the THP group.
• These effects lasted 39 months, compared to 26 months for people on THP.

Rates of serious side effects were similar in both study groups. However, more people who took trastuzumab deruxtecan experienced nausea, vomiting, and constipation. About 12 percent taking this ADC developed interstitial lung disease, though most cases were mild.

Why This Matters for People With HER2-Positive Metastatic Breast Cancer

HER2-positive metastatic breast cancer is known to be aggressive, with most people experiencing disease progression within one to two years on standard first-line treatments. For more than a decade, the THP regimen has been a standard of care, but advances have been limited.

This new study shows that, compared to THP, combining trastuzumab deruxtecan and pertuzumab may significantly delay disease progression and increase the chances of tumor shrinkage. This combination therapy kept cancer from getting worse for more than three years. It could give people with HER2-positive metastatic breast cancer more time before their cancer progresses or before they need a different medication.

As Dr. Tolaney noted, these results suggest that combining trastuzumab deruxtecan and pertuzumab “has the potential to become a new first-line standard of care for these patients.”

If you’re living with metastatic HER2-positive breast cancer and have questions about your treatment options, talk with your oncologist. Together, you can develop a regimen that meets your goals.

Learn about six treatments for HER2-positive breast cancer.

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