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Enhertu

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Enhertu (chemical name: fam-trastuzumab-deruxtecan-nxki) is approved by the U.S. Food and Drug Administration (FDA) to treat:

  • unresectable HER2-positive breast cancer
  • metastatic HER2-positive breast cancer that has been treated with two or more anti-HER2 therapies

Unresectable means the cancer can’t be removed with surgery.

Metastatic breast cancer is cancer that has spread to parts of the body away from the breast, such as the bones or liver.

Enhertu is a targeted therapy made up of three parts:

  • fam-trastuzumab: an anti-HER2 medicine that has the same basic structure as Herceptin (chemical name: trastuzumab)
  • a topoisomerase I inhibitor chemotherapy called DXd: topoisomerase I inhibitors work by interfering with the cancer cells’ ability to replicate; this type of chemotherapy is not typically used to treat HER2-positive breast cancers, so researchers believe it is less likely that the cancers will develop resistance to it
  • a compound that links the fam-trastuzumab molecule to the topoisomerase I inhibitor chemotherapy molecule

Doctors call Enhertu an antibody-drug conjugate targeted therapy. The combination of the topoisomerase I inhibitor and the linking compound is called deruxtecan. The linking compound attaches (conjugates) the fam-trastuzumab to the topoisomerase I inhibitor chemotherapy.

In earlier studies, Enhertu was called T-DXd and DS-8201.

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How Enhertu works

Some breast cancer cells make (overexpress) too many copies of a particular gene known as HER2. The HER2 gene makes a protein known as a HER2 receptor. HER2 receptors are like ears, or antennae, on the surface of all cells. These HER2 receptors receive signals that stimulate the cell to grow and multiply. But breast cancer cells with too many HER2 receptors can pick up too many growth signals and so start growing and multiplying too much and too fast. Breast cancer cells that overexpress the HER2 gene are said to be HER2-positive. About one out of every four breast cancers is HER2-positive.

Enhertu is approved by the FDA to treat metastatic HER2-positive breast cancer that has been treated with two or more anti-HER2 medicines, as well as HER2-positive breast cancer that can’t be removed with surgery.

The fam-trastuzumab part of Enhertu attaches to the HER2 protein, stopping it from receiving growth signals.

The topoisomerase I inhibitor chemotherapy part of Enhertu, like other chemotherapy medicines, interferes with cells’ ability to replicate. This type of chemotherapy is not typically used to treat HER2-positive breast cancers, so researchers believe it is less likely the cancers will develop resistance to it. The topoisomerase I inhibitor isn’t a targeted medicine, which means it can affect healthy cells as well as cancer cells.

Enhertu was designed to deliver the topoisomerase I inhibitor to cancer cells in a targeted way by attaching the topoisomerase I inhibitor to the fam-trastuzumab. The fam-trastuzumab then carries the topoisomerase I inhibitor to the HER2-positive cancer cells. This way, the topoisomerase I inhibitor is less toxic to healthy cells and more effective in treating cancer cells.

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Is Enhertu right for you?

Enhertu can be used to treat people diagnosed with metastatic HER2-positive breast cancer that has been previously treated with at least two anti-HER2 medicines.

Enhertu also can be used to treat HER2-positive breast cancer that can’t be removed with surgery.

There are several tests used to find out if breast cancer is HER2-positive. To have been previously treated with an anti-HER2 therapy, one or more of these tests was used to figure out if the cancer was likely to respond. Two of the most common tests are:

IHC (ImmunoHistoChemistry)

The IHC test uses a chemical dye to stain the HER2 proteins. The IHC gives a score of 0 to 3+ that measures the amount of HER2 proteins on the surface of cells in a breast cancer tissue sample. If the score is 0 to 1+, it’s considered HER2-negative. If the score is 2+, it's considered borderline. A score of 3+ is considered HER2-positive.

If the IHC test results are borderline, it’s likely that a FISH test will be done on a sample of the cancer tissue to determine if the cancer is HER2-positive.

FISH (Fluorescence In Situ Hybridization)

The FISH test uses special labels that are attached to the HER2 proteins. The special labels have chemicals added to them so they change color and glow in the dark when they attach to the HER2 proteins. This test is the most accurate, but it is more expensive and takes longer to return results. This is why an IHC test is usually the first test done to see if a cancer is HER2-positive. With the FISH test, you get a score of either positive or negative (some hospitals call a negative test result “zero”).

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What to expect when taking Enhertu

Enhertu is given intravenously, which means the medicine is delivered directly into your bloodstream through an IV or port. Enhertu usually is given every 3 weeks unless the cancer grows or unacceptable side effects develop.

Women who are pregnant or planning to get pregnant should not be given Enhertu. Enhertu can cause embryo death and birth defects. It’s important that you don’t get pregnant while you’re being treated with Enhertu; you must use effective birth control.

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Paying for Enhertu

If your doctor prescribes Enhertu and you have problems getting it covered by insurance or don’t have insurance, you can visit the ENHERTU4U.com patient assistance website or call 1-833-ENHERTU. The Enhertu Patient Savings Program may be able to help you with out-of-pocket costs.

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Enhertu side effects

The most common side effects of Enhertu are:

Enhertu also can cause other serious side effects. While these serious side effects are less common, it’s important to know about them:

  • Interstitial lung disease: Interstitial lung disease is a general term for disorders that cause inflammation and scarring in the lungs. The scarring makes lung tissue stiff, which makes it difficult to breathe. You should be closely monitored for signs of interstitial lung disease while being treated with Enhertu and tell your doctor right away if you experience shortness of breath or have a dry cough.
  • Heart problems: Enhertu may cause serious heart problems, including some that don’t have symptoms, such as reduced heart function, and some that do have symptoms, such as congestive heart failure. Symptoms to watch for include swelling of the ankles or legs, shortness of breath, cough, or weight gain of more than 5 pounds in less than 24 hours.

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References

  1. Enhertu prescribing information. 2019. Available at: https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/761139s000lbl.pdf (PDF).

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