The final data for Celldex Therapeutics' (NASDAQ:CLDX) cancer drug CDX-011 looks as good as the interim data did in May.

But it's still not enough to get the promising drug candidate approved.

The greatest benefit continues to be in breast cancer patients considered to be triple-negative because they don't require estrogen, progesterone, or a protein called Her2 to grow. These patients typically stop responding after a few rounds of chemotherapy, which is the stage that patients in the trial were at.

The patients also must have high expression of a protein called GPNMB because that's what CDX-011 targets. The drug is made up of an antibody against GPNMB linked to a toxic payload using technology licensed from Seattle Genetics (NASDAQ:SGEN).

The control arm allowed investigators to choose whatever chemotherapy they thought was appropriate, which produced a median survival of just 5.5 months in patients with triple-negative breast cancer and high GPNMB expression. The patients that received CDX-011 lived for 10 months.

Nearly doubling the survival was good enough to produce a statistically significant difference despite only having four patients in the chemotherapy arm and 12 patients taking CDX-011. Despite the unmet need, I think it's doubtful the Food and Drug Administration will approve the drug with such few patients, and it sounds like Celldex is planning on running a pivotal study to gain approval.

Then again, Sarepta Therapeutics (NASDAQ:SRPT) is hoping to gain accelerated approval with just four patients having taken the highest dose of its Duchenne muscular dystrophy drug, so maybe the FDA will give Celldex a Christmas present when they meet to go over the data.

Triple-negative GPNMB high expressers isn't the largest market, but Celldex has some evidence that CDX-011 works in patients that just have high expression of GPNMB. There was a solid trend in favor of survival for high GPNMB expression patients who received CDX-011 compared to those who received chemotherapy, but the difference wasn't statistically significant.

Celldex also tested CDX-011 in patients who had low levels of GPNMB. When you look at the data for all patients, the survival benefit goes away, which should give investors confidence that the effect in the high expressers is real. Just like antibody drugs without toxic payloads such as Bristol-Myers Squibb (NYSE:BMY) and Eli Lilly's (NYSE:LLY) Erbitux or GlaxoSmithKline's (NYSE:GSK) Tykerb, if the protein that the antibody targets isn't present, the drug shouldn't do much.

Celldex has a ways to go before approval, but the data today should give investors confidence that a pivotal trial will come back positive.

Fool contributor Brian Orelli has no positions in the stocks mentioned above. The Motley Fool has no positions in the stocks mentioned above. Motley Fool newsletter services recommend GlaxoSmithKline. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.