The Food and Drug Administration has ordered biotech firm Telik ( TELK) to stop all clinical trials of its experimental cancer drug Telcyta after data released this weekend showed the drug hastened the deaths of women with advanced ovarian cancer.

In a press release issued late Monday night, Telik said the FDA ordered the company to halt enrollment in all ongoing Telcyta trials. Furthermore, no patients currently being treated in the trials will be allowed to receive additional Telcyta.

Telik did not give a reason for the FDA action, except to say that the directive came after the company presented Telcyta data from phase III clinical trials at the annual meeting of the American Society of Clinical Oncology (ASCO).

In December, Telik announced that one of those trials -- dubbed Assist-1 -- had failed to show that Telcyta could improve the overall survival of women with advanced ovarian cancer compared to currently approved drugs.

But it wasn't until Sunday at an ASCO poster session -- more than five months later -- that Telik disclosed publicly just how badly Telcyta performed in the Assist-1 study. The woman treated with Telcyta died more than five months faster than similar woman in the control arm of the study.

The median survival time for women in the Telcyta arm of Assist-1 was 8.5 months. The women in the control arm of the study treated with the approved drugs doxorubicine or topetecan reported a median survival time of 13.6 months.

This negative survival effect against Telcyta was statistically significant by a wide margin, which means that, statistically speaking, it was Telcyta and not random chance that caused these women to die faster.

In a separate announcement Sunday night, Telik said that a phase III study of Telcyta in non-small-cell lung cancer patients also resulted in a negative survival effect of one and a half months. In this study, dubbed Assist-3, Telcyta patients reported a median survival of 4.6 months compared to a median survival of 6.1 months for patients in the control arm.

Telik shares fell $1.22, or 21%, to $4.59 in Monday trading as investors reacted to the negative data released over the weekend.

Telik shares have sunk 72% since late December.

But while many investors have fled the stock, activist investor Carl Icahn has been buying. In the first quarter, Icahn doubled his stake in Telik to 4.2 million shares, according to a filing with the Securities and Exchange Commission.

The Telcyta data presented at the ASCO meeting Sunday shocked many observers because it's rare to see an experimental drug hasten the death of patients to such an extent. Typically, independent safety monitors watch over a study to make sure that the drug being studied does no harm to patients.

If the drug is found to be harmful, studies can be stopped prematurely in the interest of patient safety. Why that didn't occur in the Telcyta ovarian cancer study is not known.

Telik executives could not be reached for comment.

Telik had been enrolling patients in a different study of Telcyta in ovarian cancer. In addition, several other fully enrolled studies were ongoing in which patients were receiving Telcyta.

Monday's action by the FDA forces Telik to halt new patient enrollment and to stop existing study patients from getting any more Telcyta. The company said it plans to meet with the FDA as soon as possible and to submit new Telcyta safety information.

Adam Feuerstein writes regularly for RealMoney.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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