On December 1, the FDA approved a second cancer biosimilar, trastuzumab-dkst. The drug was approved to treat patients with HER2-positive breast and metastatic stomach cancers.

The FDA has approved a second cancer biosimilar, trastuzumab-dkst (Ogivri; Mylan), to treat HER2-positive breast and metastatic stomach cancers. The biologic is a mimic of trastuzumab (Herceptin; Genentech/Roche), a monoclonal antibody that targets the HER2 protein, which is overexpressed in approximately 25%–30% of breast cancers and 20% of stomach cancers.

Trastuzumab-dkst is the first biosimilar approved to treat these particular malignancies; the first cancer biosimilar approved, bevacizumab-awwb (Mvasi; Amgen), was given the go-ahead in September to treat certain patients with lung, colorectal, brain, cervical, and kidney cancers.

Worldwide sales of Herceptin in 2016 netted Roche, Genentech's parent company, approximately $6.8 billion. Genentech maintains its patent on trastuzumab in the United States until 2019; after that, the availability of the biosimilar is expected to reduce the cost of treatment.

The agency's December 1 approval was based in part on results published online in late 2016 from the Heritage trial, which compared the two antibodies in combination with taxane chemotherapy in 458 patients with metastatic breast cancer (JAMA 2017;317:37–47). The trial, which was led by Hope Rugo, MD, of the University of California, San Francisco, found no differences in objective response rates or adverse effects between the two.

The biosimilar was approved for any indication for which trastuzumab is approved, namely, HER2-positive breast cancer of any stage and HER2-positive metastatic gastric cancer.

Gaining FDA approval for a biosimilar is a complex process, says Francisco J. Esteva, MD, PhD, director of the breast oncology program at the Perlmutter Cancer Center, NYU Langone Health in New York, NY. Esteva is the lead investigator of a recently published clinical trial of a different trastuzumab biosimilar, CT-P6 (Celltrion), in patients with early-stage HER2-positive breast cancer (Lancet Oncol 2017;18:917–28).

Because a biologic can't, by nature, be an identical copy of the original drug, biosimilars have to go through extensive testing to gain approval, Esteva says, including randomized clinical trials. “This is very different from a classic generic drug where [showing] safety and efficacy in large randomized trials is not required,” he adds.

Patients are unlikely to notice any difference. The manufacturer, Mylan, hasn't said how much trastuzumab-dkst will cost when it hits the market. Biosimilars are expected to lower treatment costs—especially when more biosimilars for the same drug become available, Esteva says.

Although the biosimilar hasn't been tested in patients with stomach cancer, Manish Shah, MD, a gastric cancer specialist at Weill Cornell Medicine in New York, NY, says that he wouldn't have any hesitation prescribing it, although he does hope further data collection (in patients with breast or stomach cancer) is done to ensure the biosimilar isn't associated with rarer adverse effects than trastuzumab itself—side effects so uncommon that the Heritage study might not have captured them.

“Even though its anticancer efficacy is likely to be the same based on this study, the more rare side effects may or may not be different,” he cautions. –Rachel Tompa

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