Shares in Genentech and Biogen Idec have taken a major hit after the firms announced disappointing data on the oncology blockbuster Rituxan, this time as a treatment for lupus.

The firms said that a 257-patient Phase II/III study of Rituxan (rituximab) for systemic lupus erythematosus did not meet its primary endpoint defined as the proportion of patients treated with the drug who achieved a major clinical or partial clinical response compared to placebo at 52 weeks. Furthermore, the study also did not meet any of its six secondary endpoints.

Hal Barron, Genentech’s chief medical officer, said the firms were disappointed with the results, “but we understood from the outset the significant challenges” in developing treatments for lupus. However all is not lost in terms of finding a treatment for the autoimmune disease which is characterised by inflammation of the joints, skin, major organs and central nervous system. He added that an ongoing Phase III trial in lupus nephritis “remains an important study as it evaluates the potential of Rituxan in a different patient population". The results from that study are expected in the first quarter of next year.

Evan Beckman, senior vice president of immunology R&D at Biogen, noted that no new therapy for lupus has been approved in more than 30 years but “we will analyse the full set of data from this trial in the coming months, share the findings with regulatory authorities, and apply the key insights to our continued research in lupus".

The news comes just after Genenetech and Biogen revealed data from a Phase II/III study of Rituxan which showed that the drug failed to prove effective as a treatment for primary-progressive multiple sclerosis. Analysts were not sure how big a market there was for an MS indication for Rituxan, which is approved as a treatment for non-Hodgkin's lymphoma and rheumatoid arthritis, and the same seems to apply to lupus.

Nevertheless, investors were non-plussed and Genentech’s stock slumped 7.5% to %67.93, while Biogen shares fell 5.16% to $61.33.