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 that any biosimilar drug go through the same rigorous clinical trials that original biologic drugs do before the agency will approve the biosimilar.
A study suggests that a drug that is a biosimilar to Herceptin, called CT-P6, is as effective and as safe as Herceptin.
The research was published online by The Lancet Oncology. Read the abstract of “CT-P6 compared with reference trastuzumab for HER2-positive breast cancer: a randomised, double-blind, active-controlled, phase 3 equivalence trial.”
The results also were presented at the 2017 American Society of Clinical Oncology (ASCO) Annual Meeting on June 4, 2017.
This is the second Herceptin biosimilar to have results published and presented at an ASCO annual meeting. In 2016, researchers reported that the Herceptin biosimilar MYL-1401O given with taxane chemotherapy to treat women with HER2-positive, metastatic breast cancer was just as safe and as effective as Herceptin.
In this study, 549 women diagnosed with stage I to stage IIIA HER2-positive breast cancer were randomly assigned to receive one of two treatments before surgery:
- CT-P6 plus the chemotherapy medicine Taxotere (chemical name: docetaxel) for the first four cycles, then CT-P6 plus fluorouracil, Ellence (chemical name: epirubicin), and Cytoxan (chemical name: cyclophosphamide) -- the combination of fluorouracil, Ellence, and Cytoxan is a common chemotherapy combination and is often abbreviated FEC -- for the last four cycles
- Herceptin plus Taxotere for the first four cycles, then Herceptin plus FEC for the last four cycles
Chemotherapy given before surgery is called "neoadjuvant" chemotherapy. All the medicines are given intravenously.
None of the women had received breast cancer treatment before.
All the women had surgery to remove the breast cancer 3 to 6 weeks after the final CT-P6 or Herceptin treatment.
One way doctors judge the effectiveness of neoadjuvant chemotherapy 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:
- 46.8% of women treated with CT-P6 had a pCR
- 50.4% of women treated with Herceptin had a pCR
The CT-P6 and Herceptin also had similar safety profiles:
- 7% of women treated with CT-P6 had a serious side effect
- 8% of women treated with Herceptin had a serious side effect
Neutropenia -- low white blood cell counts -- was the most common serious side effect.
The experimental biosimilar CT-P6, made by Celltrion, 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 CT-P6 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 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 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.