Biosimilars are a new type of medicine 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. Biologic medicines used in breast cancer treatment are trastuzumab (Herceptin) and pertuzumab (Perjeta), both used in HER2-positive disease.

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.

Since 2015, 11 biosimilars have come into use in the U.S., 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. They will become available when the patent on trastuzumab expires in 2019.


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. So 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.


Who gets biosimilars for breast cancer

Biosimilars for cancer treatment

Right now, the only breast cancer treatment with FDA-approved biosimilars is trastuzumab. Other manufacturers can’t sell biosimilars until the patent on Herceptin, the brand name of trastuzumab, ends. The patent, held by the company Genentech, expires in 2019, at which point people may be able to get a biosimilar recommended by their doctor instead of the original trastuzumab. As of July 2019, the FDA has approved five biosimilars for trastuzumab:

  • Trazimera (trastuzumab-qyyp)
  • Ontruzant (trastuzumab-dttb)
  • Ogivri (trastuzumab-dkst)
  • Herzuma (trastuzumab-pkrb)
  • Kanjinti (trastuzumab-anns)

Biosimilars for side effect management

Other biosimilars are FDA approved to treat the side effects of chemotherapy. They are

  • filgrastim-sndz (Zarxio), biosimilar of filgrastim (Neupogen)
  • pegfilgrastim-jmdb (Fulphila), biosimilar of pegfilgrastim (Neulasta)

Both filgrastim-sndz and pegfilgrastim-jmdb 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.


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 like low white blood cell counts, 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.


Reviewed and updated: July 17, 2019

Reviewed by: William J. Gradishar, MD, FACP


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