In other words, in order to show any survival advantage for Prochymal protocol 275, not only did Osiris need to employ a dubious historical control group, but it had to separate the GVHD patients by disease severity. Osiris has never adequately explained why Prochymal benefits children with GVHD but not adults, nor has it explained why Prochymal only seems to prolong survival in children with more severe grades of GVHD while not helping less sick patients. When Canada granted conditional approval for Prochymal in May, Osiris CEO Randy Mills told the New York Times that the company filed first in Canada because the U.S. Food and Drug Administration had told the company it would need additional data before seeking approval here. The newly released Canadian regulatory documents show our neighbors to the North, despite approving Prochymal, are not yet convinced that the stem cell therapy benefits GVHD patients. FDA isn't going to be as lenient, which puts Osiris in a tough spot fundamentally, even if it has momentum traders on its side for now. @zortrades asks, "What is your take on $ARNA?" There's frenzied trading in Arena Pharmaceuticals ( ARNA) ahead of the June 27 FDA approval decision for the weight-loss drug lorcaserin. Take a look at the StockTwits heat map for health care: The trader twitter chatter is dominated by Arena! StockTwits executive editor Phil Pearlman has more details on the incredible 4,321% rise in social media traffic for Arena over the past three months. Staggering numbers. It was noted by someone else (I don't know who) that FDA announced the three-month delay in the Vivus ( VVUS) Qnexa review eight days before the approval decision date. We are now past that eight-day mark for Arena, so perhaps the risk of a similar delay for lorcaserin is diminished, if not gone entirely. I'm predicting full approval of lorcaserin on June 27. Of course, I've been wrong about Arena and lorcaserin in the past, so... I can't help but think that momentum traders are largely behind Arena's run-up into the FDA decision date. Short covering and a cult-like retail investor following are helping, too. Don't believe me? Check out the InvestorVillage.com message board where Arena cult leaders rant endlessly about the evils of short selling and threaten to sue anyone for criminal conspiracy just because they don't like the stock. At some point, traders will take profits, leaving Arena's stock price vulnerable. Whether that happens immediately upon lorcaserin's approval or days later isn't clear to me. Your guess is as good as mine.