What Are Biosimilars?

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

Biosimilars are drugs that are very similar to an already-approved biologic drug. Biologics are drugs made from living cells. These cells can come from parts of the blood, proteins, viruses, or tissue. This process turns the cells into drugs that can prevent, treat, and cure disease.1

Generic drugs have the same active ingredient and are equivalent to a brand drug. However, biosimilars are more complex to develop. They are known as “highly similar” to their original product. Biosimilars are usually less expensive than their reference medicine. They also provide another treatment option for people with certain medical conditions.1

When comparing biosimilars to their reference biologic, biosimilars:1

  • Are made with the same kinds of natural sources
  • Are given the same way
  • Have the same strength and dose
  • Have the same possible side effects
  • Give the same treatment benefits

Biosimilars are evaluated for safety, quality, and effectiveness before they receive approval. The US Food and Drug Administration (FDA) only approves biosimilars that have no major differences from the approved reference drug.1

The FDA-approved biosimilars for breast cancer are all biosimilars to Herceptin® (trastuzumab).1-3

How do trastuzumab biosimilars work?

About 1 in 5 women with breast cancer have too much of a protein called human epidermal growth factor receptor 2 (HER2). These cancers are known as HER2-positive breast cancers. They grow and spread aggressively.2

Trastuzumab biosimilars are targeted therapies. It is a monoclonal antibody. A monoclonal antibody is a type of immune system protein that is made in a lab. The drug attaches to the HER2 protein on cancer cells. This helps stop the cells from growing.2

Examples of trastuzumab biosimilars for breast cancer

There are several Herceptin biosimilars used to treat certain types of breast cancer, including:2

What are the possible side effects?

The most common side effects of trastuzumab biosimilars include:4-8

  • Fever
  • Nausea, vomiting
  • Diarrhea
  • Infusion reactions
  • Infections
  • Cough
  • Headache
  • Tiredness
  • Shortness of breath
  • Rash
  • Low levels of white blood cells (neutropenia)
  • Low levels of red blood cells (anemia)
  • Muscle pain

Trastuzumab products have a boxed warning, the strictest warning from the FDA. This is because they may cause severe side effects, including:4-8

  • Heart problems, such as congestive heart failure or reduced heart function
  • Infusion reactions, which may cause fever, chills, nausea, vomiting, pain, headache, dizziness, and/or shortness of breath
  • Serious harm to an unborn baby, which may cause birth defects or death
  • Severe lung damage
  • Worsening of chemotherapy-induced reductions in white blood cells

These are not all the possible side effects of trastuzumab biosimilars. Talk to your doctor about what to expect when taking a trastuzumab biosimilar. You also should call your doctor if you have any changes that concern you when taking a trastuzumab biosimilar.

Other things to know

Your doctor will check your heart function before and during treatment with trastuzumab.

Before taking a trastuzumab biosimilar, tell your doctor if you:4-8

  • Are allergic to trastuzumab
  • Have or have had heart disease
  • Are being treated with radiation therapy to the chest or with other chemotherapy drugs
  • Have or have had lung disease, a tumor in your lungs, or difficulty breathing

Trastuzumab biosimilars can harm an unborn baby. If you can become pregnant, you should use birth control during treatment and for some time after the last dose of the drug. You should also not breastfeed during treatment with a trastuzumab biosimilar and for some time after the last dose. Talk to your doctor about your options for birth control and breastfeeding while taking a trastuzumab biosimilar.4-8

Before beginning treatment for breast cancer, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you are taking. This includes over-the-counter drugs.

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