Biosimilars are medicines made by copying brand-name biologics. Biologics are medicines made from living cells, rather than chemicals. These cells might come from an animal, plant, bacteria, or other microbe. The biologic medicines approved to treat HER2-positive breast cancer are trastuzumab (Herceptin), pertuzumab (Perjeta), and margetuximab (Margenza).

It can be helpful to think of biosimilars as similar to generic versions of these biologic medicines. Generic medicines are copies of brand-name medicines made from chemicals. A good example is acetaminophen, which is the generic version of Tylenol.

Like generics, biosimilars are designed to work just as well as the brand-name biologic. But unlike generics, biosimilars can never be exact copies of the original biologic medicines, since they’re made using living material. In the case of biosimilars, the Food and Drug Administration determines that they are close enough to the original medicine, based on rigorous testing, to have similar effectiveness, safety, and side effects.

In the U.S., biosimilars have been approved for a variety of health issues. Some treat different types of arthritis as well as gastrointestinal diseases such as Crohn’s disease and ulcerative colitis. Others boost white blood cell counts during chemotherapy for cancer.

Trastuzumab is the first—and only—breast cancer treatment for which there are FDA-approved biosimilars.


How biosimilars work

Any biosimilar is designed to work in the same way as the brand-name biologic it copies. The manufacturer doesn’t have access to the cell lines (living material) that the original maker used, or to their processes and technology. Researchers have to study how each different biologic medicine works and figure out how to produce their own version.

The FDA requires a biosimilar to go through testing in the lab and in animals to show that it delivers the same amount of active ingredient in the same way as the original medicine. Then it has to be compared with the original medicine in people. The studies must show that the biosimilar works equally well in treating the condition as the original. It also has to be equally as safe as the brand-name version, and have similar or fewer side effects.


Biosimilars used in breast cancer treatment

Biosimilars for HER2-positive breast cancer

The FDA has approved six biosimilars for trastuzumab, which treats HER2-positive breast cancer:

  • Trastuzumab-anns (Kanjinti)
  • Trastuzumab-dkst (Ogivri)
  • Trastuzumab-dttb (Ontruzant)
  • Trastuzumab-qyyp (Trazimera)
  • Trastuzumab-pkrb (Herzuma)
  • Trastuzumab-strf (Hercessi)


Biosimilars for side effect management

Other biosimilars are FDA approved to treat the side effects of chemotherapy and endocrine therapy. They are:

  • Biosimilars of filgrastim (Neupogen):
    • Filgrastim-sndz (Zarxio)
    • Filgrastim-aafi (Nivestym)
    • Filgrastim-ayow (Reuleuko)
  • Biosimilars of pegfilgrastim (Neulasta):
    • Pegfilgrastim-apgf (Nyvepria)
    • Pegfilgrastim-bmez (Ziextenzo)
    • Pegfilgrastim-cbqv (Udenyca)
    • Pegfilgrastim-fpgk (Stimufend)
    • Pegfilgrastim-jmdb (Fulphila)
    • Pegfilgrastim-pbbk (Fylnetra)

Biosimilars for filgrastim and pegfilgrastim can boost white blood cell counts during chemotherapy, just like the biologic medicines they copy. Boosting white blood cell counts helps prevent people on chemotherapy from getting infections.

Denosumab-bbdz (Jubbonti) is a biosimilar for the bone-strengthening medicine denosumab (Prolia). Both drugs are approved for use in people taking adjuvant aromatase inhibitors for hormone receptor-positive breast cancer. They work to increase bone mass and reduce the risk of bone loss and fracture in people taking aromatase inhibitors.



How biosimilars are given

Biosimilars are given in the same way as the original brand-name biologics. All of the biosimilars available to treat breast cancer so far are given by IV infusion. It requires going to your doctor’s office, hospital, or treatment center.

If you’re offered a biosimilar for a side effect such as low white blood cell counts or risk of fracture, you may be given an injection—a shot—that can be done in the doctor’s office or, in some cases, at home.



Biosimilar side effects

The side effects of any biosimilar are the same as those caused by the medicine it copies.

For example, trastuzumab-dkst has the same potential side effects as trastuzumab. These include headache, diarrhea, nausea, chills, fever, infection, difficulty sleeping, cough, and rash. Both medicines pose a rare but serious risk of heart problems that can usually be resolved by stopping the medicine or taking heart medicine.

Similarly, filgrastim-sndz has the potential to cause the same side effects as filgrastim, such as bone and joint pain, muscle pain, headache, nosebleeds, fever, trouble breathing, rash, and itching. Both also can cause pain in the upper left part of the stomach or tip of the left shoulder, and they have some risk of spleen rupture.

Common side effects of denosumab-bbdz include pain in the joints, muscles, back, arms, and legs. More serious side effects include low calcium levels in the blood, allergic reactions, infections, skin rash, jaw problems, and broken bones after stopping denosumab-bbdz.


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Reviewed and updated: May 28, 2024

Reviewed by: William J. Gradishar, MD, FACP


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