Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Geron (NASDAQ:GERN), a clinical-stage biopharmaceutical company focused on developing therapies to treat cancer, dipped as much as 20% after filing an 8-K with the Securities and Exchange Commission before the opening bell, which briefly updated the Mayo Clinic's ongoing study of imetelstat in patients with myelofibrosis.

So what: According to the 8-K filing, the investigator-sponsored trial (IST) has been closed to new patients, with the company estimating 79 patients had been enrolled in the Mayo Clinic's IST. The filing also notes that "20 patients have discountinued from the study since its inception." Geron notes that the additional accrued safety and efficacy data should be sufficient to support its push to move imetelstat into a phase 2 trial in the first-half of 2014.

Now what: It's not painted out in black and white like things normally are in the biotech arena, but investors appear to be displeased with the high number of patients who dropped out of the study when it didn't appear safety or toxicity were a big issue when the Mayo Clinic released its findings in early December. Obviously, imetelstat offers a lot of promise based on these early studies done by the Mayo Clinic. As we saw in December, some of the study's patients demonstrated partial, and even complete, responses -- and a complete response is incredibly rare when dealing with myelofibrosis. In other words, imetelstat may still offer a bright future, but it's probably not worth getting too worked up over this experimental drug until we have a larger cohort of patients tested in phase 2 trials. Then we can more clearly see the drug's efficacy and safety profile, and make a smarter investing decision.

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Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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