Updated from 6:14 am EDT with new information.

Geron (GERN) - Get Report received a call from the FDA yesterday which no drug developer ever wants: A full clinical hold has been placed on its lead drug imetelstat due to concerns about liver toxicity.

The FDA-mandated full clinical hold requires Geron to suspend enrollment in all of its imetelstat clinical trials. 


The clinical hold affects the remaining eight patients in the company`s Phase 2 study in essential thrombocythemia (ET) or polycythemia vera (PV) and the remaining two patients in the company`s Phase 2 study in multiple myeloma. In addition, the company's planned Phase 2 clinical trial in myelofibrosis will likely be delayed due to the clinical hold. It is possible that other studies using imetelstat, such as ongoing investigator-sponsored trials, may also be placed on clinical hold by the FDA.

It's the Mayo Clinic-sponsored study of Imetelstat in patients with myelofibrosis which had put Geron back on the investor map because of early data suggesting the drug might be capable of reversing the underlying cause of the disease. No word yet on whether FDA has also asked Mayo Clinic to suspect its imetelstat clinical trials, although such a request will not be a surprise now. 

The FDA placed imetelstat on full clinical hold due to "the occurrence of persistent low-grade liver function test (LFT) abnormalities observed in the Phase 2 study of imetelstat in ET/PV patients and the potential risk of chronic liver injury following long-term exposure to imetelstat," Geron said.

Geron is holding a conference call later this morning. No word yet from the company about how long this clinical hold will last or what will be required to demonstrate to FDA that the drug is safe enough to continue clinical studies. 

Geron shares are down 67% to $1.42 in Wednesday trading. Watch trading in other myelofibrosis-related stocks this morning as well, including Incyte (INCY) - Get Report, Cell Therapeutics (CTIC) - Get Report and Gilead Sciences (GILD) - Get Report

I'll leave you with this thought:

Update: On a conference call this morning, Geron said the FDA concerns relate primarily to reports of "persistent" low-grade elevations in liver enzymes reported by almost all imetelstat-treated patients. Regulators want Geron to submit clinical data on the reversibility of these liver toxicity signals.

Dirk Haussecker, a consultant, RNAi expert and blogger, posted this morning on a possible explanation for why imetelstat could be causing liver toxicity. It's worth a read. 

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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