A Phase 3 clinical trial comparing Mylan’s proposed biosimilar trastuzumab with the original Herceptin (trastuzumab) found no difference between the drugs in effectiveness or safety, suggesting that the biosimilar may be a viable option for women with ERBB2-positive metastatic breast cancer.
Biosimilars are copies of biological drugs that show comparable effects to the original compound, and research shows that such compounds both increase access and reduce costs for treatment. Mylan plans to conduct further studies to assess how the biosimilar performs in the long run.
The study, “Effect of a Proposed Trastuzumab Biosimilar Compared With Trastuzumab on Overall Response Rate in Patients With ERBB2 (HER2)–Positive Metastatic Breast Cancer,” was published in the journal JAMA.
The clinical trial (NCT02472964) randomized 500 women to receive either Herceptin or the biosimilar, combined with chemotherapy with either Taxol (paclitaxel) or Taxotere (docetaxel). Nearly an equal number received the proposed biosimilar as were given Herceptin, with 230 and 228 women in each group.
After the initial 24 weeks, women with a stable disease continued treatment with the biological drug only for an additional 24 weeks.
Researchers from the University of California San Francisco and Mylan report that after 24 weeks of treatment, the overall response rate was 69.6 percent in the group receiving the proposed biosimilar trastuzumab. This was no different from what was achieved with Herceptin, which had an overall response rate of 64 percent. The difference was within the boundaries set by regulatory authorities in Europe.
At the trial’s end, no differences were seen between the proposed biosimilar and Herceptin on several measures. At week 48, 41.3% of patients receiving Mylan’s biosimilar experienced tumor progression, compared to 43.0% in the Herceptin group.
Likewise, progression-free survival was 44.3% for the proposed biosimilar, and 44.7% for Herceptin. And overall survival was 89.1% percent in the biosimilar group after 48 weeks, compared to 85.1 percent in the Herceptin group.
The trial also evaluated the safety of the proposed biosimilar, and found similar rates of adverse events in the two groups — 96.8% of patients in the proposed biosimilar, and 94.7% in the Herceptin group experienced at least one adverse event. Serious adverse events were reported by 38.1% and 36.2% in the biosimilar and Herceptin groups, respectively.
The study also found no difference in the rate of immune reactions to the two treatments, with 2.4% in the proposed biosimilar trastuzumab group and 2.8% in the Herceptin group developing antibodies against the treatment.