With the Nasdaq Biotechnology Index up 65% since the start of the year, it's clear that the biotech sector performed extraordinarily well in 2013-but which stocks were the biggest winners? Several small-cap and mid-cap biotech companies posted returns of 200% or more through the middle of December this year, and, in this series, I'll review the 15 biggest movers of 2013. Let's continue this review with number 11 on the list, Geron Corporation (NASDAQ:GERN).

As fellow Fool George Budwell pointed out, this isn't Geron's first rodeo. The company has been around more than 20 years and so far its success has been anything but spectacular.

Yet investor enthusiasm returned in force this year, driving shares up 238% through the middle of December on hopes Geron's drug imetelstat can kick-start a winning streak.

A nausea inspiring roller-coaster ride

Geron has taken shareholders on a wild ride this past decade, rallying to as much as $12 in 2005 and falling to as low as less than $2 last year. There have been plenty of booms and busts along the way and that means those hanging onto shares from as recently as 2008 remain underwater despite the impressive jump this year.

GERN Chart

GERN data by YCharts

Clearly, investors hope better times and bigger profits may be ahead. The company had to scuttle its brain cancer drug last year and all of Geron's efforts have since shifted to ushering imetelstat through trials as a treatment for myelofibrosis, a type of chronic leukemia.

So far, that appears to be a good bet. In November, results from a small study showing four myelofibrosis patients went into complete remission following treatment were released in an abstract for presentation at the American Society of Hematology conference.

In addition to the four complete responders, another person went into partial remission and three others saw their condition improve. However, before we get too excited, this data comes from a tiny 18 person patient pool.  

Regardless, it gave Geron -- and those patients -- some hope that imetelstat could prove the first treatment with the potential for complete remission.

If imetelstat ever does see the commercialization light-of-day, it would go up against Incyte Corporation's (NASDAQ:INCY) Jakafi, a drug designed to reduce the size of the spleen rather than cure the disease.   Sales of Jakafi, which was approved for MF in November 2011, grew 11% in Q3 from Q2, prompting the Incyte to reaffirm the high end of its full year $220 million to $230 million sales guidance.

Fool-worthy final thoughts

It's been a hard couple of years for Geron's pipeline. The company shuttered its lead candidate, a brain cancer treatment, last year after a phase 2 study failed. And while imetelstat got good news this year, it previously stumbled as a treatment for breast cancer when its control arm outperformed it in trials. That suggests investors should approach this early stage imetelstat data with caution.

The ability to offer hope to the 176,000 patients diagnosed with myelofibrosis in the United States, however, shouldn't be discounted. But all but the most risk tolerant investors will need to see more advanced data before they commit to Geron -- data which may still be years away.

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Todd Campbell has no position in any stocks mentioned.  Todd owns E.B. Capital Markets, LLC.  E.B. Capital's clients may or may not have positions in the companies mentioned.  Todd also owns Gundalow Advisors, LLC.  Gundalow's clients do not have positions in the companies mentioned. The Motley Fool has no position in any of the stocks mentioned. 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.