Doctors are convinced that Truxima, the first rituximab biosimilar approved by the FDA, is as effective as rituximab; European experience with the biosimilar over the last 2 years has also revealed no problems with unexpected side effects. However, cost will be a factor in determining whether doctors in the United States prescribe Truxima instead of rituximab.

In late November, the FDA approved a biosimilar, rituximab-abbs (Truxima; Celltrion), for the widely used CD20-specific antibody rituximab (Rituxan; Genentech). Physicians say they would be inclined to switch to prescribing this biosimilar for non-Hodgkin lymphoma (NHL), but whether they will get the chance to do so will depend on the drug's cost.

Truxima is the 15th biosimilar to earn the FDA's nod, but the first for rituximab. Two phase III clinical trials, both evaluating the biosimilar in follicular lymphoma, a common form of low-grade NHL, provided evidence for the decision. One trial recorded a 95.7% objective response rate (ORR) among 140 patients given the biosimilar, compared with 90% for rituximab. In the second trial, involving 258 patients, the ORRs were 83.1% and 81.3%, respectively. Both studies showed similar side-effect profiles for Truxima and rituximab.

Stephen Ansell, MD, PhD, of the Mayo Clinic in Rochester, MN, says the data have convinced him that rituximab and the biosimilar are equivalent. “The efficacy and toxicity are the same,” he says. However, rituximab does retain one advantage over the biosimilar, Ansell notes. It can be given with a subcutaneous injection, whereas the biosimilar requires an intravenous infusion and thus a longer clinic visit.

Mitchell Smith, MD, PhD, of George Washington University Cancer Center in Washington, DC, says that given the current evidence, he would prescribe the biosimilar instead of rituximab. But one possible difference between the two drugs does bear watching, he says. Although their amino acid sequences are identical, the two antibodies may carry different combinations of the sugars that affect target binding. If that's the case, Truxima might trigger a response from the patient's immune system that could reduce its effectiveness and, in rare cases, result in autoimmune reactions. No signs of such reactions have been reported so far, but “we need to keep an eye out,” says Smith. If they don't occur, “we will be truly comfortable” with the biosimilar, he says.

Europe's experience with the biosimilar has been reassuring, adds Anas Younes, MD, of the Memorial Sloan Kettering Cancer Center in New York, NY. Truxima has been on the market there since 2017, along with another rituximab biosimilar, Rixathon (Sandoz), which the FDA rejected. “We have not heard of any issues since Truxima was approved in Europe,” says Younes, and physicians there are prescribing the drug. “Truxima now has about a 30% market share,” he notes.

Truxima's price in the United States, which Celltrion hasn't announced, will dictate how many prescriptions doctors here write, says Ansell. Given how entrenched rituximab is in cancer treatment, the biosimilar will have to cost substantially less to get onto hospital formularies, he says. “It needs to be something where people would say, ‘Oooh, there's a deal.’” –Mitch Leslie

©2018 American Association for Cancer Research.
2018
American Association for Cancer Research.