Seven sentences is all it took to send Geron (GERN 1.28%) down as much as 20% today. That was the total length of Geron's disclosure in an 8-K filed with the Securities and Exchange Commission today.

Let's break it down and see what's got investors hitting the sell button.

In November 2012, Dr. Ayalew Tefferi (the "investigator"), of Mayo Clinic, initiated an investigator-sponsored clinical trial to evaluate imetelstat in patients with myelofibrosis and other myeloid malignancies (the "Myelofibrosis IST"). 

Nothing new here. Geron spent most of 2013 waiting for data from Tefferi's investigator-sponsored clinical trial before deciding what to do with imetelstat.

Mayo Clinic has informed Geron Corporation (the "Company" or "Geron") that effective January 22, 2014, the Myelofibrosis IST has been closed to new patient enrollment, and that the remaining patients in the study will continue to receive imetelstat treatment and be followed under the Myelofibrosis IST protocol.

Closing enrollment is new, but not unexpected. This was a proof-of-concept study, investors can't expect the Mayo Clinic to do all the work; Geron is going to have to run a trial of its own. In fact, you could argue that ending enrollment in the trial is helpful because it allows Geron to enroll any new patients that would have gone to Mayo's trial.

The Company believes that approximately 79 patients have been enrolled in the Myelofibrosis IST, including nine patients with blast-phase myelofibrosis and nine patients with refractory anemia with ringed sideroblasts ("RARS"), a subpopulation of myelodysplastic syndromes, and that approximately 20 patients have discontinued from the study since its inception.

It seems like the last part of that sentence is what's setting off investors. Oh no, 20 patients out of 79 have discontinued; that's 25% of the patients!

Except we know nothing about the patients. It's possible patients are dropping out because of safety concerns, which would obviously be bad.

But my guess is most dropped out because imetelstat wasn't working for them. Progression of myelofibrosis can lead to fatal leukemia, so there isn't much reason to continue on a drug that isn't working.

When Geron updated investors at the American Society of Hematology meeting in December, there were nine discontinuations out of the 33 patients that had safety data to draw from, or 27% of the patients, essentially the same as the current dropout rate. Of the nine dropouts, six discontinued because of lack of efficacy. Assuming the same rate, investors have little to worry about with this new disclosure.

Remember, the corollary to 25% dropping out is that 75% of patients stayed in the study, presumably because they had some belief that imetelstat works.

In December 2013 at the American Society of Hematology Annual Meeting, the investigator presented preliminary data from the first two cohorts of patients in the Myelofibrosis IST, including preliminary efficacy data for 22 patients and preliminary safety data for 33 patients.

Nothing new here. It's pretty clear imetelstat is able to send some patients into remission, something we haven't seen from Incyte's (INCY 0.72%) Jakafi, the only approved drug for myelofibrosis.

Based on this preliminary efficacy and safety data, the Company plans to initiate a Geron-sponsored, multi-center, Phase 2 clinical trial of imetelstat in patients with myelofibrosis in the first half of 2014.

That's the expected next step. Investors are likely getting antsy about the trial beginning, but planning trials takes time.

The Company also believes that the total accrued patients in the Myelofibrosis IST will be adequate for gathering additional and updated safety and efficacy data to support the imetelstat development program.

And that's a good point. Data from the other half of the patients will help determine who should be enrolled, and the dosing regimen for Geron's trial. Speed is clearly important, here; if waiting will improve the likelihood of success for the next trial, investors should be patient.

The Company expects that the investigator will present at a future medical conference additional and updated safety and efficacy data, including longer-term durability, for those patients previously reported and for additional remaining patients in the Myelofibrosis IST.

With data from Geron's trial a year or more away, investors will be following Tefferi around to every conference, hoping for a new nugget to give increased confidence that imetelstat is working.

Data on the rest of the patients are important, but investors should also be looking for long-term data on patients that went into remission. To be clearly better than Incyte's Jakafi, imetelstat not only has to send patients into remission, but it has to keep them there for an extended period of time.