BOSTON -- I'm not one to shy away from controversy, so I'll get right to the point: I've spent a few days digging into Medarex's ( MEDX) skin cancer drug MDX-010. What I found wasn't very impressive. I don't believe the current phase III studies are going to yield positive data strong enough to warrant the drug's approval. The drug, which also goes by the name ipilimumab, just isn't very potent when used by itself (as monotherapy) in patients with advanced melanoma, or skin cancer. That's the conclusion I draw from a look at previously conducted clinical trials. If a drug fails to impress in phase II trials, it's hard to have much confidence in a successful outcome from phase III trials. That's conventional wisdom in the biotech sector -- and it usually serves investors well. Medarex shares had been moving strongly in the past three months as investors await the results from a trio of phase III monotherapy studies of MDX-010 in patients with advanced melanoma. The stock closed Friday at $15.55, off more than 6%. The data are expected before the end of the year, hopefully in September or October. These are registration studies, which means that if they're successful, Medarex and partner Bristol-Myers Squibb ( BMY) say they will file for the drug's approval with the Food and Drug Administration.