MENLO PARK, Calif. ( TheStreet) -- Updated results from a small study of Geron's (GERN) - Get Report experimental myelofibrosis drug imetelstat disclosed Thursday yielded a remission rate of 21%, essentially unchanged from results presented one year ago, with significant side effects. 

Geron shares fell 6% to $2.48 in mid-morning trading. The new imetelstat data in myelofibrosis are contained in a just-released research abstract ahead of next month's American Society of Hematology ASH annual meeting

According to the abstract, seven of 33 myelofibrosis patients who were treated with imetelstat have achieved a complete or partial remission. The 21% remission rate compares with a 22% remission rate (five of 22 patients) presented at last year's ASH meeting. Six of the seven patients remain in remission for a median of 9.9 months, according to the abstract.

A complete or partial remission means myelofibrosis patients had a response in their bone marrow and resolution of clinical symptoms such as reductions in the size of their spleens. Myelofibrosisis is a cancer-like disease in which abnormal bone marrow stem cells produce scar tissue. This scar tissue, or fibrosis, crowds out and replaces healthy marrow.

No myelofibrosis drug has ever before demonstrated the ability to clear bone marrow fibrosis, i.e. reverse the underlying cause of myelofibrosis. Imetelstat might be the first, which is why the drug attracted so much investor interest last year when initial study results were announced.  Incyte's (INCY) - Get Report myelofibrosis drug Jakafi was approved only on the ability to reduce spleen size The drug does nothing to clear bone marrow fibrosis. 

But since then, imetelstat has run into safety problems. In February, the FDA placed a clinical hold on further development of imetelstat due to concerns about liver toxicity. The clinical hold was removed just this month, allowing Geron to move ahead with new studies of imetelstat in myelofibrosis. 

According to Thursday's abstract, elevated liver enzyme levels -- a marker for liver toxicity -- were detected in about half of the myelofibrosis patients treated with imetelstat. The drug also causes significant reductions in red and white  blood cells.

Additional and updated study results on imetelstat will be presented at the ASH meeting next month. Geron has already announced plans to begin a larger, phase II study of imetelstat in myelofibrosis in the first half of next year.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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