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 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 ABP 980, is as safe as and as effective as Herceptin.
The research was published in the June 2018 issue of The Lancet Oncology. Read the abstract of “Efficacy and safety of ABP 980 compared with reference trastuzumab in women with HER2-positive early breast cancer (LILAC study): a randomised, double-blind, phase 3 trial.”
The study analysis included 696 women diagnosed with early-stage, HER2-positive breast cancer. All the women were scheduled to have chemotherapy before surgery to remove the breast cancer.
After four cycles of anthracycline-based chemotherapy before surgery, the women were randomly assigned to receive one of two treatments:
- ABP 980: a loading dose followed by three cycles (358 women)
- Herceptin: a loading dose followed by three cycles (338 women)
Medicines given before surgery are called neoadjuvant treatments. All the medicines were given intravenously.
The women had surgery 3 to 7 weeks after the last dose of ABP 980 or Herceptin.
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.
The pCR rates were similar between the two treatment groups:
- 172 women treated with ABP (48%) had a pCR
- 137 women treated with Herceptin (41%) had a pCR
In the neoadjuvant part of the study, severe side effect rates were similar between the two groups:
- 54 women (15%) treated with ABP 980 had a severe side effect
- 51 women (14%) treated with Herceptin had a severe side effect
The most common severe side effect was neutropenia, which is low levels of certain white blood cells. About 6% of the women in each group had severe neutropenia.
After surgery, the women were treated with either ABP 980 or Herceptin every 3 weeks for up to 1 year after the first dose. The women were randomly assigned to either:
- continue treatment with ABP 980
- continue treatment with Herceptin
- switch from Herceptin to APB 980
Treatment given after surgery is called adjuvant treatment.
In the adjuvant part of the study, the severe side effect rates continued to be similar for all the treatment groups:
- 9% of women continuing on ABP 980 had a severe side effect
- 6% of women continuing on Herceptin had a severe side effect
- 8% of women who switched from Herceptin to ABP 980 had a severe side effect
The most common severe side effects in the adjuvant setting were infection, neutropenia, and infusion reactions.
Experimental ABP 980, made by Amgen, is not approved by the FDA. On June 1, 2018, The FDA issued a Complete Response Letter for ABP 980, which means that the agency has completed its review and decided that it will not approve ABP 980 for marketing in its present form.
However, on May 30, 2018, ABP 980, under the brand name Kanjinti, was listed on the European Medicines Agency (EMA) website as authorized for marketing by the European Commission. The EMA said Kanjinti is approved to treat early-stage and metastatic HER2-positive breast cancer.
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.
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.
To connect with others who are managing a HER2-positive diagnosis, join the Breastcancer.org Discussion Board forum HER2+ (Positive) Breast Cancer.
Editor’s Note: On Dec. 14, 2018, the FDA approved the biosimilar Herzuma (chemical name: trastuzumab-pkrb), previously known as CT-P6, to treat people with HER2-positive breast cancer.