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What happened

Celldex Therapeutics (NASDAQ:CLDX) stock was up as much as 12.3% today, but has given a little back, trading up 8.4% at 12:57 p.m. EDT after Brean Capital started coverage on the biotech with a "buy" rating and a $16 price target.

So what

Last week, the European Society for Medical Oncology (ESMO) abstracts for poster presentations were released, including Celldex Therapeutics' abstract for its presentation of clinical trial data for its lead drug, glembatumumab vedotin, in melanoma.

Of the 57 patients in the study who could be evaluated, one had a complete response and seven had a partial response, combining for an objective response rate of 14%. That's not too shabby considering these are advanced patients, with more than half having failed three or more prior therapies.

Celldex Therapeutics decided that it needed to see six responders in the first 52 patients -- an 11.5% objective response rate -- to deem the clinical trial successful. From the abstract, it isn't clear how patients 53-57 fared, but management already disclosed that the threshold was exceeded.

Abstracts have to be turned in months before the meeting, so the data is only up to date as of April. At that point, there were another five patients enrolled whose tumors hadn't been assessed yet, which will likely be presented at ESMO on Monday. We may also get more information, such as progression free survival or even overall survival data.

Now what

Regardless of the analyst buy rating, some investors are probably buying Celldex Therapeutics as a short-term play ahead of ESMO in the hopes that the up-to-date data is positive. Long-term investors could be in for a bumpy ride this week.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.