Rituxan (rituximab) is a chimeric (mouse/human) antibody that targets CD20. It was originally developed by researchers at IDEC Pharmaceuticals and was approved by the U.S. Food and Drug Administration (FDA) in 1997 for the treatment of B cell non-Hodgkin lymphomas resistant to other chemotherapy regimens. It is currently co-marketed by Biogen and Genentech in the United States, Hoffmann–La Roche in Canada and the European Union (as MabThera) and Chugai Pharmaceuticals and Zenyaku Kogyo in Japan.

The patents have expired, however, and several companies have developed or are developing biosimiliars of the drug, with products approved in India, the European Union, Switzerland, Japan and Australia. 

Pfizer is developing a rituximab biosimilar (of PF-05280586) and recently reported the results of a comparative safety and efficacy study of PF-05280586 versus Rituxan/MabThera. The proposed biosimilar met its primary endpoint of overall response rate (ORR, the percentage of patients achieving complete response [CR] or partial response [PR]) at week 26 of the 52-week study. No clinically meaningful differences in efficacy were observed between PF-05280586 and MabThera when administered to patients as a first-line treatment for CD20+, low–tumor burden follicular lymphoma (LTB-FL). Estimated rates of one-year progression-free survival were also similar across groups.