Herceptin (chemical name: trastuzumab) is 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 monoclonal antibody. 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 (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 Myl-1401O, is as effective and as safe as Herceptin.
The research was reported at the 2016 American Society of Clinical Oncology Annual Meeting on June 3, 2016. Read the abstract of “Heritage: A phase III safety and efficacy trial of the proposed trastuzumab biosimilar Myl-1401O versus Herceptin.”
The results are the first to show that a biosimilar to an approved biologic drug has the same effects on cancer as the original drug, according to Hope Rugo, M.D., professor of medicine at the University of California, San Francisco, Helen Diller Family Comprehensive Cancer Center and lead author of the study. Dr. Rugo also is a member of the Breastcancer.org Professional Advisory Board.
In the study, 458 women diagnosed with metastatic, HER2-positive breast cancer were randomly assigned to receive one of two treatments:
- Herceptin with either Taxol (chemical name: paclitaxel) or Taxotere (chemical name: docetaxel)
- Myl-1401O with either Taxol or Taxotere
The women received a minimum of eight cycles of treatment.
None of the women had been treated with chemotherapy or Herceptin for metastatic disease, and 44% of the women had breast cancer that also was hormone-receptor-positive.
Metastatic breast cancer is cancer that has spread away from the breast area to another part of the body, such as the liver or bones.
Neither the doctors nor the women knew which medicine the women were getting.
After 24 weeks, the researchers looked to see how the cancers were responding to the treatment. Overall response rates were:
- 69.6% for Myl-1401O
- 64% for Herceptin
The risk of serious side effects also was similar for the two drugs:
- 38% of women getting Myl-1401O had a serious side effect
- 36% of women getting Herceptin had a serious side effect
Most of the serious side effects were related to low white blood cell counts, which doctors call neutropenia. When you have a low white blood cell count, your immune system doesn’t work as well as it should and you’re more likely to get an infection.
The experimental biosimilar Myl-1401O has not been approved by the FDA yet, though Mylan, the company that makes Myl-1401O, has said it might be sent to the FDA later this year.
Dr. Rugo said in an interview that if the new biosimilar is approved by the FDA, it could allow more access to treatment for women diagnosed with HER2-positive breast cancer.
“Lack of access is not a major issue in the United States,” she said, “because most patients have insurance that covers trastuzumab. I’ve not seen a situation where it wasn’t covered for a standard indication.”
Still, in other countries, cost can mean that some women don’t receive the treatment.
“It is expected that having biosimilars will reduce costs -- by some amount -- for these agents around the world,” Dr. Rugo said. Still, it is unclear how much less expensive biosimilars will be.
These results seem promising, but it’s not clear when or if Myl-1401O will be approved for use in the United States.
While Myl-1401O is the first biosimilar cancer drug to be reported on, 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.