Pfizer (NYSE:PFE) and Celldex Therapeutics are in a sticky situation, but they're making the best of it.

They've had to change their clinical trial for their brain cancer drug, CDX-110, in midstream -- never a good sign -- but at least they've got a good excuse. The phase 2b part of their phase 2b/3 combination was an open-label, two-arm controlled trial. That's clinical speak for: The patients knew that they were getting either standard of care, Schering-Plough's (NYSE:SGP) Temodar, or that plus CDX-110. Since there was no placebo and the patients knew which arm they were in -- that's the open-label part -- most patients in the Temodar-alone arm dropped out of the trial.

To try and salvage the experiment, Pfizer and Celldex changed the trial to a single-arm phase 2 trial: Everyone's getting Temodar plus CDX-110. However, now the companies will have to run a separate phase 3 trial, assuming the results are positive.

There are two ways for investors to look at this change:

  1. Open-label trials are difficult to evaluate. They make it much harder for investors to predict whether the drug will pass pivotal phase 3 trials using data from a non-blinded phase 2.
  2. The fact that so many patients ditched the trial when they were assigned to the standard-of-care arm means that there's potentially a great market. Apparently patients are looking for more than just the current standard of care.

Considering that Temodar is on its way to becoming a blockbuster, with $760 million in sales through the first nine months of the year, I'm inclined to look at this as a positive. If CDX-110 can improve the survival results of Temodar by just a little bit, there's clearly a large market for the drug.

Of course the potential delay could be costly. According to clinicaltrials.gov, Novartis' (NYSE:NVS) Gleevac recently completed a phase 3 trial testing the already-approved drug in the same type of brain cancer. Eli Lilly (NYSE:LLY) also has a phase 3 trial testing its drug candidate enzastaurin against Bristol-Myers Squibb's (NYSE:BMY) CeeNU for a similar tumor type. Those trials are for recurring brain cancer, but they'll likely try for a front-line indication should they prove successful in these trials.

Only time will tell what the competitive landscape will look like when CDX-110 is finally up for approval a few years from now, but Pfizer and Celldex are certainly doing their best to get to that point as quickly as possible.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.