Shares of drug developer Genta ( GNTA) plummeted Friday after the company announced that regulators have deemed its proposed blood cancer treatment not approvable.

Genta sank 18.7% to 56 cents in morning trading. The company was seeking clearance from the Food and Drug Administration to market Genasense for treatment of chronic lymphocytic leukemia, in combination with chemotherapy.

We are keenly disappointed by this decision," said Genta's CEO, Dr. Raymond P. Warrell Jr. "We believe that Genasense has amply demonstrated its efficacy and safety in patients with relapsed and refractory CLL in a carefully designed and executed randomized clinical trial."

The company said that while it decides on its next steps with U.S. regulators, it will continue seeking approval of Genasense in other countries for patients who have advanced cancer.

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