If you're a biotech investor, you might have been pleasantly surprised by your stocks' performances on Monday, especially if your holdings include small or mid-sized companies that are targeting cancer. The Biotech HOLDRS (AMEX:BBH) rose over 2%, nearly twice as much as the broader market averages.

The reason: the American Association for Cancer Research (AACR) meeting going on in Orlando is highlighting many advances in cancer treatment, detection, and prevention. These meetings feature scientists from industry and academia, but it's usually the industry presentations that get the biotech investor's pulse rate up.

But there's a problem: You have to be in Orlando to see them. That's no problem, say the biotechs, we'll put out press releases to keep our dear investors informed! And so there is a plethora of clinical trial updates, basic research leads, and general progress reports.

Naturally, these press reports are all very encouraging, and so the job of sorting out the truly impressive news from the merely upbeat falls to the investor.

Generally, I would advise a biotech investor to ignore most of the preclinical data presented at these conferences, unless the data show something really new or spectacular. The old joke about how many times we've cured cancer in mice is true. It's quite difficult even for a "pro" to sort out preclinical data, so I look for human trial results.

Dendreon (NASDAQ:DNDN) is one such company trumpeting its human trial results in Orlando. Readers may remember that Dendreon's most-studied therapy is for prostate cancer, but the company is showing that it's not a one-trick pony by releasing results of a phase 1 trial for breast cancer.

Usually phase 1 trials do not have much data showing efficacy, but this one was an exception. Results showed that three out of 18 patients with advanced, metastatic breast cancer who had failed both Genentech's (NYSE:DNA) Herceptin regimen and chemotherapy achieved prolonged stabilization of their disease lasting up to 22 months. Impressively, this stabilization occurred without additional chemotherapy. As a result, Dendreon shares climbed more than 4%.

Besides cautioning investors on reading too much into preclinical data, I would also caution against buying in the middle of all the conference "buzz." As volatile as these small biotechs are, the investor can often wait a few days or weeks and buy in at a lower price. For example, OXiGENE (NASDAQ:OXGN) jumped 15% on news that its OXi4503 compound showed promise in mouse models of breast and ovarian cancers. While this news is better than the compound not working, is it really worth an added $20 million in market capitalization? To be fair, OXiGENE does have human trial data, but those trials were not being updated at the conference, to my knowledge.

It's likely that there will be several more such "winners" who will emerge from this conference. I hope your stocks are among them!

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Fool contributor David Nierengarten, Ph.D., works with a biotechnology venture capital fund. He is an active member of the TMF community as DavidMN, and enjoys the Biotechnology discussion board. He holds no positions in any of the companies listed.