Trastuzumab Biosimilar Yields Similar Response Rates in HER2-Positive Breast Cancer

A biosimilar yielded equivalent response rates to trastuzumab at 24 weeks in a study of women with HER2-positive metastatic breast cancer also receiving taxanes. Safety and long-term outcomes remain to be studied with the biosimilar option.

“Patient access to biologics is limited in many countries,” wrote study authors led by Hope S. Rugo, MD, of the Helen Diller Family Comprehensive Cancer Center at the University of California, San Francisco. “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.”

The new study compared trastuzumab with the biosimilar known as MYL-14010 in 458 women (493 in a safety population). The study was double-blind and randomized, and included only patients with HER2-positive metastatic breast cancer; it was conducted across 95 sites in Europe, India, South Africa, Thailand, and elsewhere. The results were published in JAMA.

The overall response rate was 69.6% in the biosimilar group, and 64.0% in the trastuzumab group, for a ratio between the two of 1.09 (90% CI, 0.974–1.211). The confidence interval fell with a predefined equivalence boundary for the biosimilar. The equivalence was also seen in a per-protocol population of 438 patients (original 458-patient group was intention-to-treat).

In secondary efficacy analyses, 41.3% of patients in the biosimilar group had tumor progression at week 48, compared with 43.0% of patients in the trastuzumab group (P = .68). The time to progression was not different between the two groups. A hazard ratio for progression-free survival also showed no difference between the groups.

Most patients in both groups had at least one treatment-emergent adverse event (96.8% with biosimilar and 94.7% with trastuzumab). Most adverse events were mild or moderate, and 7 patients in each group (2.8%) reported an event that led to treatment discontinuation. A total of 94 patients (38.1%) in the biosimilar group and 89 patients (36.2%) in the trastuzumab group had at least one serious adverse event, with neutropenia, febrile neutropenia, and leukopenia being the most common. There were four deaths related to adverse events in each group, and one in each group due to respiratory failure was considered “possibly related” to the study drug.

“A biosimilar treatment option may increase global access to biological 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 authors wrote. The results of this study are consistent with earlier research showing similar pharmacokinetics to trastuzumab, but further study is still needed to assess long-term clinical outcome and safety.