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 various types of cancer, jumped as much as 18% after an encouraging study by the Mayo Clinic demonstrated the effectiveness of Geron's experimental myelofibrosis drug, imetelstat.

So what: According to Bloomberg, the Mayo Clinic study involved 22 myelofibrosis patients who were studied for at least six months. The study notes that five patients achieved a partial or complete remission, while 41% of patients overall responded to the therapy. What's really exciting about this study, despite it being arguably small, is that complete responses in treating myelofibrosis are extremely rare, signaling the potential benefit that imetelstat could bring to patients.

Now what: I certainly won't take anything away from the Mayo Clinic's published results, but I continue to feel that Geron shareholders could be playing with fire here. At the moment for Geron, it's imetelstat or bust. This isn't to say that imetelstat hasn't delivered in clinical trials thus far (because it has), but I would point out that one drug over two clinical indications isn't a very diverse pipeline. I would contend that much of imetelstat's positive news of late has been baked into Geron's share price, and it wouldn't take much to knock Geron off its high horse if something didn't go its way with its lead drug. My suggestion would be to wait for a significant pullback or late-stage data to stream in before we get too excited about Geron's prospects.

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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