If you’re being treated with trastuzumab (Herceptin) you may soon be offered a new version of this drug called a biosimilar.

If you have been diagnosed with HER2+ breast cancer, you’ll be offered treatment with the drug trastuzumab. Until recently, there was only one brand of this drug available, called Herceptin. But three new brands are now being offered in England, called Ontruzant, Herzuma and Kanjinti. They are also referred to as trastuzumab biosimilars.

Why are new versions of trastuzumab being introduced?

Trastuzumab (Herceptin) was previously protected by a patent, meaning only the company that developed it was allowed to make and sell it. This patent has recently expired, and other companies are now allowed to make their own versions. These are likely to be cheaper than Herceptin, meaning the NHS can continue to provide important treatment for HER2+ breast cancer while making valuable savings.

Identical copies of most drugs can be made using their chemical formula. But trastuzumab is a biological, not a chemical drug – it’s a complex molecule made by living cells, meaning it’s not possible to copy it exactly. Ontruzant, Herzuma and Kanjinti have been developed to work in the same way as Herceptin and have exactly the same effect, but they are not completely identical to Herceptin. This is why they are also known as biosimilars.

The NHS already uses other biosimilars to treat conditions such as blood cancer and arthritis.

Will I be offered a trastuzumab biosimilar?

Whether you are offered treatment with a trastuzumab biosimilar (Ontruzant, Herzuma or Kanjinti) will depend on the type of breast cancer you have and your specific treatment plan. This is because trastuzumab biosimilars can only be given through a drip into a vein (intravenously), and this method is normally only used to treat certain types of HER2+ breast cancer. Herceptin can be given as injections under the skin (subcutaneously) as well as through a drip.

You can discuss this in more detail with your oncologist or breast care team. It’s important that you are involved in treatment decisions and have the opportunity to ask questions.

If you’re going through treatment:

You may be asked to switch to a biosimilar if you’re currently having Herceptin treatment through a drip. This will usually be the case if:

You’re likely to continue on Herceptin if you’re currently receiving injections of Herceptin under the skin. This will usually be the case if:

  • You have HER2+ primary breast cancer and your treatment is being given after surgery (called adjuvant treatment)

If you’re about to start treatment:

You’re likely to start treatment with a biosimilar rather than Herceptin if your treatment will be given through a drip. This will usually be the case if:

  • You’ve just been diagnosed with HER2+ primary breast cancer and you have been offered trastuzumab before surgery (called neoadjuvant treatment) alongside another drug called pertuzumab (Perjeta)
  • You’ve just been diagnosed with HER2+ secondary breast cancer

Both Herceptin and trastuzumab biosimilars follow the same treatment schedule. If you’re being treated for primary breast cancer this will normally be every three weeks for a year. If you’re being treated for secondary breast cancer this will normally be every three weeks, or sometimes every week, for as long as your cancer is under control.

Do trastuzumab biosimilars work as well as Herceptin?

Thorough lab tests on trastuzumab biosimilars have shown that they have highly similar properties to Herceptin and work in the same way. Clinical trials in women with early breast cancer have also shown that trastuzumab biosimilars are as effective at treating HER2+ breast cancer as Herceptin, and just as safe.

Under this strict system of testing, a number of other biosimilars have been used safely and effectively by the NHS for many years.

Herceptin can be used in several different treatment plans, and biosimilars have not been directly tested in all of them. But experts are satisfied from the existing evidence that trastuzumab biosimilars are so similar to Herceptin that they can be used in all the same ways.

Are there any side effects of trastuzumab biosimilars?

Thorough testing (see above) has shown that the potential side effects of trastuzumab biosimilars are the same as Herceptin. Common side effects include flu-like symptoms, diarrhoea and nausea. Some women experience an allergic reaction to the treatment, although this is rare. 

Treatment with trastuzumab biosimilars or Herceptin can also cause heart problems. Your breast care team will monitor your heart function before and throughout your treatment, and your treatment may be temporarily suspended if there is any sign of a heart problem developing.

Talk to your breast care team if you experience any problems as they can help you manage any side effects.

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