Rigel’s fostamatinib hits PhIII goal, but shares yo-yo on data

California biotech Rigel Pharmaceuticals ($RIGL) has posted positive new late-stage data for its experimental thrombocytopenia treatment and says it is eyeing a 2017 submission to the FDA.

But while fostamatinib, its oral spleen tyrosine kinase (SYK) inhibitor, hit its primary endpoint, only 18% of the 76 patients saw a stable platelet response, compared to none on the placebo arm. Analysts had previously believed low- to mid-20s was the likely target, although 18% still reaches statistical significance. 

There were also a high number of AEs, with treatment-related AEs at 77% for the med, but just 28% on the placebo arm. GI complaints were the most observed adverse event on fostamatinib.

Shares had been trading up by 50% premarket this morning before the data were released at 7am ET--but then dropped by more than 9% within minutes of the figures being posted. This then rebounded to be up by around 40% by midday. The drug could reach peak annual sales of $300 to $400 million, according to estimates. 

This is the first of two double-blind studies in the FIT Phase III programs for the treatment of adult chronic/persistent immune thrombocytopenia (ITP). Results from the second study are expected in October/November 2016.

The biotech is still trying to see this as a positive however, saying in a release that if these results are reproduced it will likely go for an NDA with the FDA in the first quarter of 2017. 

"These data demonstrate the potential benefit of fostamatinib for chronic ITP patients who are in need of new treatment options," said Raul Rodriguez, president and chief executive officer of Rigel.

"We believe that fostamatinib has significant commercial potential given that it has a unique mechanism of action that may work where other products have failed."

"We are very encouraged by these results," added Anne-Marie Duliege, executive vice president and chief medical officer of Rigel.

"Consistent with the prior clinical study of fostamatinib in ITP, this FIT Phase III study demonstrated that fostamatinib provided a robust and enduring benefit for those patients who responded to the drug candidate."