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 hematologic myeloid malignancies, were pummeled, falling as much as 68% after it announced a full clinical hold of its investigational new drug, imtelelstat, which has ongoing studies in essential thrombocythemia and multiple myeloma.

So what: According to Geron's press release before the opening bell this morning, the Food and Drug Administration gave verbal notice to the company yesterday afternoon that the full clinical hold would be "due to the occurrence of persistent low-grade liver function test (LFT) abnormalities observed in the phase 2 study of imetelstat in [essential thrombocythemia] patients and the potential risk of chronic liver injury following long-term exposure to imetelstat. The FDA was also concerned whether or not these abnormalities will be reversible." This clinical hold will likely delay the start of a phase 2 myelofibrosis study, and puts a halt to the ongoing study of essential thrombocythemia and multiple myeloma, which had eight and two patients still being tested, respectively.

Now what: This is a monumental letdown for Geron shareholders as imetelstat is Geron's entire pipeline at the moment -- but it shouldn't be a complete shock. If you recall, in late January we discovered through an 8-K filing that the investigator-sponsored myelofibrosis trial being conducted by the Mayo Clinic and utilizing imetelstat had an inordinately high number of dropouts (20 of 79 patients). If there were a clue that problems may have been on the horizon, I believe that was it. If there's some sort of LFT abnormality that persists following additional study from the FDA, it could present a death knell for the drug. Of course, we have to keep in mind that plenty of drugs have also been removed from clinical hold after a review and allowed to continue their development without a hitch. In the meantime, Geron will need to fall back on its remaining $56 million in cash and ride out the storm, hoping in the back of its mind that the FDA lifts the clinical hold. As for me, I'd suggest keeping a very safe distance from Geron.

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.