For a company that didn't conduct any of its own clinical trials in 2013, Geron (NASDAQ:GERN) sure had a banner year, hitting a strong share-price triple and then some.

GERN Chart

GERN data by YCharts .

The late-year run came from an investigator-sponsored clinical trial using Geron's cancer drug imetelstat. The drug as of last year failed to show an effect in breast cancer patients, but regained new life when a trial in patients with a blood disorder called essential thrombocythemia produced positive results.

Batting .500 -- and really less than that, since Geron also ended a trial in lung cancer early -- the company held off on conducting a trial, deciding to wait for results from a trial being run by investigators at the Mayo Clinic in patients with myelofibrosis.. Both diseases start in the bone marrow where cells divide uncontrollably, so there was a reasonable chance that imetelstat would work in myelofibrosis despite the failures in solid tumors.

Data presented in an abstract ahead of the American Society of Hematology meeting in December confirmed the hypothesis, and the actual presentation cleared up some loose ends. Imetelstat appears to be sending myelofibrosis patients into complete remission, something Incyte 's (NASDAQ:INCY) Jakafi -- the only drug approved to treat myelofibrosis -- isn't capable of doing. Cell Therapeutics (NASDAQ:CTIC) is developing pacritinib and Gilead Sciences (NASDAQ:GILD) has momelotinib for myelofibrosis patients, but both drugs are in the same class as Jakafi and are more likely to treat the symptoms of myelofibrosis patients than the underlying issue. Gilead has a second drug, simtuzumab, that acts through a different target, but I don't think there's enough data to know if it could produce the disease-modifying results that imetelstat has shown.

A more productive 2014 
Geron won't be able to rely on investigator-sponsored clinical trials to drive its share price further. It'll need to run a pivotal trial of its own to confirm the tantalizing data from the early trial to get imetelstat approved by the regulatory authorities.

Spontaneous complete remissions are extremely rare in myelofibrosis patients, so there's a low risk that the drug doesn't pass its next clinical trial. The level of remissions -- five out of 22 patients in the Mayo Clinic trial -- might drop a little in a larger trial, but even if it's half that level, it'll be considered best in class.

Safety issues are the biggest risk for Geron's investors as it proceeds ahead. Thrombocytopenia -- a decrease of platelets in blood -- was seen in many of the patients in the Mayo Clinic trial. While it's a manageable condition, the thrombocytopenia could limit which patients get the drug. Doctors aren't particularly fond of drugs with small therapeutic windows (a small range of dosage where the drug is efficacious but not toxic).

I like the risk-reward profile at this level, but investors are going to have to be patient and wait for the next clinical trial that's scheduled to begin in the first half of 2014. Depending on when it wraps up, I think another triple in 2014 is probably unlikely.

Fool contributor Brian Orelli has no position in any stocks mentioned. The Motley Fool recommends Gilead Sciences. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.