SAN FRANCISCO – Several factors must be considered when extrapolating biosimilar results, according to a speaker at the National Comprehensive Cancer Network Hematologic Malignancies Annual Congress.
In this context, “extrapolation” means expanding the use of an approved biosimilar from one indication to another, based on efficacy and safety data from the first indication,, of Memorial Sloan Kettering Cancer Center, New York, explained at the meeting.
To determine if extrapolation is appropriate, regulatory agencies consider the biosimilar’s mechanism of action in each indication; pharmacokinetics, pharmacodynamics, and immunogenicity in the different patient populations; differences in expected toxicities for each condition and population; and any other factor that may affect safety or efficacy.
To illustrate the process, Dr. Zelenetz explained how results with a rituximab biosimilar in rheumatoid arthritis (RA) cannot be extrapolated to B‐cell non‐Hodgkin lymphoma (NHL), but results with that same biosimilar in follicular lymphoma can be extrapolated to other types of B-cell NHL.
The biosimilar is rituximab-abbs (CT‐P10, Truxima). In a phase 1 trial of patients with RA, rituximab-abbs demonstrated biosimilarity to the reference product ().
The RA results cannot be extrapolated to B-cell NHL for a few reasons, according to Dr. Zelenetz. He noted that rituximab’s mechanism of action is antibody-dependent cell‐mediated cytotoxicity in both RA and NHL. However, the target in RA is the normal B cell, and the target in NHL is the malignant B cell.
In addition, the pharmacokinetics of rituximab are “drastically different” in RA and NHL, Dr. Zelenetz said. Differences in pharmacokinetics support different dosing approaches in the two diseases.
Another big difference is immunogenicity. Anti‐CD20 antibodies develop in 15%-17% of RA patients, Dr. Zelenetz said, but the risk of antibody development is less than 1% in lymphoma.
Though extrapolation from RA to B‐cell NHL was not possible, it was possible to extrapolate results with rituximab-abbs in follicular lymphoma to other B-cell NHLs.
The study used was a phase 3 trial comparing rituximab-abbs to rituximab – both in combination with cyclophosphamide, vincristine, and prednisone – in patients with newly diagnosed, advanced stage follicular lymphoma.
This study showed no difference in pharmacokinetics or pharmacodynamics between rituximab-abbs and rituximab. The two agents also had comparable safety profiles and produced similar response rates ().
Rituximab‐abbs wasbased on these data, and results from this trial were extrapolated to other types of B-cell NHL. The results were extrapolated because the mechanism of action, pharmacokinetics, pharmacodynamics, and immunogenicity of rituximab are the same across B-cell NHLs, Dr. Zelenetz noted.
“Extrapolation is a critical part of biosimilarity development,” he said. “As long as scientific justification for extrapolation exists, I believe that extrapolation makes good sense.”
Dr. Zelenetz reported relationships with AbbVie, Adaptive Biotechnologies, Amgen, AstraZeneca, BeiGene, Celgene, Genentech, Gilead Sciences, Janssen, MEI Pharma, MorphoSys AG, Novartis, Pharmacyclics, and Roche.