Cell Genesys ( CEGE) landed a partner for its experimental prostate cancer vaccine. The South San Francisco-based biotech outfit announced Monday night that Japanese drug maker Takeda Pharmaceutical has signed on as a global partner for GVAX Prostate, currently in phase III clinical trials. As a highly visible and vocal Cell Genesys bear, this is where many people out there may expect me to express how wrong I've been about GVAX Prostate. Clearly, this Takeda partnership is a vindication of Cell Genesys' approach to developing an immunotherapy against prostate cancer; and the new deal assures investors that the ongoing phase III GVAX Prostate cancer trials will be positive once we start seeing data next year. The problem, however, is that I don't really believe any of that. Sure, I'll congratulate Cell Genesys and its CEO Stephen Sherwin on landing a partner willing to fork over cash to gain rights to GVAX Prostate. And certainly, I expect Cell Genesys shares to trade higher for a time. In advance of the Takeda partnership, Cell Genesys shares closed Monday down a penny to $2.35 a share. The stock was up 86 cents, or 37%, to $3.21 a share in after-hours trading. But the Takeda deal doesn't change the fact that the clinical data backing GVAX Prostate to date come from non-randomized, i.e. uncontrolled, studies. In other words, it's not very reliable. I'm not a believer in GVAX Prostate. I don't think the data collected to date are very impressive, and I won't be surprised to see the phase III studies fail. That's especially true of the first of these studies, which pits GVAX Prostate head to head against the chemotherapy drug Taxotere. There are two companies that Cell Genesys admirers should keep in mind: Novacea ( NOVC) and Schering-Plough ( SGP). Last May, Novacea landed the Big Pharma giant as a partner for its prostate cancer drug Asentar. Novacea shares ripped higher. Well, that party didn't last long, and it ended badly. Novacea shares began sliding soon after the deal was announced. Then in November, the partnership blew up when the Asentar study was stopped because of too many deaths in the Asentar arm of the phase III study. Does anyone think Schering-Plough believed Asentar was a bust when it agreed to hand over a big chunk of change to Novacea? I doubt it. Time will tell if Takeda is making a similar mistake with Cell Genesys.