Among women with metastatic breast cancer, treatment with a drug that is biosimilar to the breast cancer drug trastuzumab resulted in an equivalent overall response rate at 24 weeks compared with trastuzumab, according to a study published online by JAMA.

Biological agents, including monoclonal antibodies, have increased the treatment options and greatly improved outcomes for a number of cancers.

However, patient access to these biologics is limited in many countries.

With impending patent expiration of some biological agents, development of biosimilars has become a high priority for drug developers and health authorities throughout the world to provide access to high-quality alternatives.

A biosimilar drug is a biological product that is highly similar to a licensed biological product, with no clinically meaningful differences in terms of safety or potency.

Treatment with the anti-ERBB2 humanised monoclonal antibody trastuzumab and chemotherapy significantly improves progression-free and overall survival in patients with ERBB2 (HER2)-positive metastatic breast cancer.

In this multicenter, phase 3 study, Hope S. Rugo, M.D., of the University of California San Francisco Helen Diller Family Comprehensive Cancer Center, and colleagues randomly assigned patients with ERBB2-positive metastatic breast cancer to receive a proposed trastuzumab biosimilar (MYL-14010) (n = 230) or trastuzumab (n = 228) with a taxane (a chemotherapy agent) to compare the overall response rate and safety after 24 weeks.

Chemotherapy was administered for at least 24 weeks followed by antibody alone until unacceptable toxic effects or disease progression occurred.

Tumour progression was assessed every 6 weeks.

The primary outcome was week 24 overall response rate defined as complete or partial response.

The overall response rate was 70 percent for the proposed biosimilar vs 64 percent for trastuzumab.

At week 48, there was no statistically significant difference with the proposed biosimilar vs trastuzumab for time to tumour progression (41 percent vs 43 percent), progression-free survival (44 percent vs 45 percent), or overall survival (89 percent vs 85 percent).

In the proposed biosimilar and trastuzumab groups, 99 percent and 95 percent of patients had at least 1 adverse event.

"Trastuzumab is not widely available around the world," the authors write. "A biosimilar treatment option may increase global access to biologic cancer therapies, provided, among other issues, that the price of the biosimilar is sufficiently inexpensive to enable women in non-high-income countries to access this therapy."

The researchers note that further study is needed to assess safety as well as long-term clinical outcome.

Source: JAMA