Will Biosimilar Trastuzumab Change Clinical Practice?

Trastuzumab has been used to manage both early and metastatic HER2-postive breast cancer with encouraging results. It has significantly improved the survival of these patients and become the standard of care, according to an editorial by Arlene Chan, MBBS, FRACP, MMed, writing in Chinese Clinical Oncology. However, the cost of 12 months of adjuvant trastuzumab therapy, the standard duration of treatment, as well as the cost associated with indefinite use in a metastatic setting, limits patient access to this life-saving drug.

According to Chan, a study published in the Lancet Oncology that evaluated trastuzumab’s limited availability in China, India, and Russia (which make up 40% of the world’s population) showed that only one-third of HER2-positive breast cancer patients in China had access to trastuzumab. The study also demonstrated equivalence of the biosimilar, CT-P6, with reference trastuzumab in the primary outcome measure of pathological complete response (pCR). In line with the FDA’s guidance on using pCR as an endpoint in high-risk early-stage breast cancer following neoadjuvant therapy to support accelerated drug approval, the use of pCR is an appropriate clinical endpoint to demonstrate equivalence of the 2 molecules, said Chan.

With respect to safety, incidence of treatment emergent adverse events appeared to be balanced between the 2 agents. The administration of concurrent anti-HER2 agent with the anthracycline component of neoadjuvant treatment did not show differences in rates of symptomatic cardiac dysfunction, though cardiac function follow-up was only reported until the end of the neoadjuvant phase of treatment. Investigators will also perform a follow-up for disease events for a minimum of 3 years from the enrollment of the last patient to ensure that the equivalent efficacy is maintained.

According to Chan, the real benefit of the study will be determining whether the presumed lower drug costs of the biosimilar translate into greater utilization of this targeted therapy, especially for those who do not currently receive this treatment. The healthcare community is waiting to see whether increasing availability of trastuzumab biosimilar agents will change clinical practice as the financial barriers are lowered.

It will also be important, says Chan, to measure certain outcomes as more biosimilars enter the clinical setting for breast cancer and HER2-positive solid tumors. These outcomes will include institutional and national data collection to show that more patients are receiving this therapy, as well as cost savings that are presumed for health care providers.