Herceptin (chemical name: trastuzumab) is a monoclonal antibody, a targeted therapy medicine used to treat HER2-positive breast cancers. Herceptin is what’s called a “biologic” drug. This means that it is made from living organisms, in this case a protein from a mouse cell. A monoclonal antibody is a type of protein made in the lab that can bind to substances in the body, including cancer cells. Each monoclonal antibody is made so that it binds only to one substance. Herceptin binds to the HER2 receptor proteins in cancer cells.
Because they are made from living organisms, biologic drugs are much more complex to make than conventional drugs that are made from a mixture of chemicals. The chemical structure of conventional drugs can be easily identified and duplicated, which is why there are so many generic drugs on the market.
A biosimilar is a new type of biologic drug. A biosimilar is almost identical to a biologic drug that is already approved by the U.S. Food and Drug Administration (FDA) (or similar organizations in other countries). It can help to think of a biosimilar as a generic version of a biologic drug, though that comparison isn’t completely accurate.
The makers of biosimilars don’t have access to the original cell lines used to make the biologic drug. They also don’t have access to the exact purification process or other manufacturing steps used by the makers of the biologic drug.
Biologic drugs can be very sensitive to changes in the manufacturing process. If one small step is done differently, the biosimilar may have very different effects than the original biologic drug.
So, the FDA requires the makers of biosimilars to show that a biosimilar drug is “highly similar” to the original biologic drug and is equally safe and effective before the agency will approve the biosimilar.
A study suggests that a drug that is a biosimilar to Herceptin, called SB3, is as effective and as safe as Herceptin.
The research was published online on Jan. 26, 2018 by the Journal of Clinical Oncology. Read the abstract of “Phase III, Randomized, Double-Blind Study Comparing the Efficacy, Safety, and Immunogenicity of SB3 (Trastuzumab Biosimilar) and Reference Trastuzumab in Patients Treated With Neoadjuvant Therapy for Human Epidermal Growth Factor Receptor 2-Positive Early Breast Cancer.”
In this study, 800 women diagnosed with early-stage, HER2-positive breast cancer from April 2014 to August 2015 were randomly assigned to receive one of two treatments:
- SB3 at the same time as chemotherapy before surgery for eight cycles, then surgery, then 10 cycles of SB3 after surgery (402 women)
- Herceptin at the same time as chemotherapy before surgery for eight cycles, then surgery, then 10 cycles of Herceptin after surgery (398 women)
Medicines given before surgery are called "neoadjuvant" treatments. All the medicines are given intravenously.
One way doctors judge the effectiveness of neoadjuvant treatments is to look at the tissue removed during surgery to see if any actively growing cancer cells are present. If no active cancer cells are present, doctors call it a “pathologic complete response” or pCR.
Several studies have shown an association between pCR after neoadjuvant chemotherapy for breast cancer and better disease-free survival, as well as better overall survival.
Disease-free survival is how long a woman lives without the breast cancer coming back. Overall survival is how long a woman lives, with or without the breast cancer coming back.
The pCR rates were similar for each treatment group:
- 45.8% of women treated with SB3 had a pCR
- 35.8% of women treated with Herceptin had a pCR
SB3 and Herceptin also had similar safety profiles:
- about 95% of women in both groups had at least one treatment side effect
- 10.5% of women treated with SB3 had a serious side effect
- 10.7% of women treated with Herceptin had a serious side effect
The most common side effects in both groups were:
- neutropenia -- low white blood cell counts
- hair loss
Experimental SB3, made by Merck and Samsung Bioepsis, has not been approved by the FDA yet.
Some doctors think that biosimilars will allow more access to treatment for women diagnosed with HER2-positive breast cancer because biosimilars are expected to cost less than the reference drugs.
While these results are promising, it’s not clear when or if SB3 will be approved for use in the United States.
Biosimilar drugs are being developed by a number of different companies. It’s likely that there will be more studies in the future. So stay tuned to Breastcancer.org for the latest information on biosimilar drugs for breast cancer and what that might mean for you.
Editor's Note: On Jan. 18, 2019, the FDA approved Ontruzant (chemical name: trastuzumab-dttb), a biosimilar for Herceptin to treat people diagnosed with HER2-positive breast cancer. Ontruzant was previously known as SB3. On Dec. 14, 2018, the FDA approved Herzuma (chemical name: trastuzumab-pkrb), a biosimilar for Herceptin to treat people with HER2-positive breast cancer. Herzuma was previously known as CT-P6. This article was updated on Sept. 27, 2019, to clarify information about biosimilars.
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