Twice as many patients who stopped taking a Pfizer Inc. anti-blood-clotting drug in a trial of cancer patients died, compared with those taking another anti-clotting drug, U.S. regulators said on Tuesday ahead of Pfizer’s request for wider approval of the drug.

New York-based Pfizer, the world’s largest drugmaker, plans on Wednesday to request that an FDA advisory panel on back the use of the drug, Fragmin, for treating and preventing blood clots in cancer patients. Fragmin is already approved for treating clots in abdominal surgery patients, among other uses.

“The most notable safety findings were that, compared with the (generic anti-clotting drug) group, more Fragmin patients discontinued the assigned study drug due to death and the patients on Fragmin experienced numerically higher rates of major bleeding,” and other major side effects, FDA staff said in their report.

Pfizer officials were not available for comment.

FDA staff highlighted the drug discontinuation issue for the advisory panel’s discussion. The agency takes the advice of its expert panels into consideration when weighing an approval, but is not bound by their recommendation.

Total mortality rates among all patients in the Fragmin study were similar for the two groups. The higher death rate was among all patients who stopped taking part in the trial, whether for blood clots, other adverse events, or death.

The FDA staff also noted the submission of only one clinical trial is a “limitation” to Pfizer’s bid to expanded use.

Japan’s Eisai Co Ltd. owns the rights to promote Fragmin in the United States.