U.S. drug reviewers questioned the value of preventing blood clots with Sanofi SA's semuloparin injection for cancer patients receiving chemotherapy.
The Food and Drug Administration staff said only a small number of people in the clinical trials for semuloparin actually had issues with clotting, and most people died from other problems.
"These findings call into question the clinical value of semuloparin in the proposed clinical setting," the FDA reviewers said in documents posted online on Monday.
The FDA staff review comes ahead of an advisory panel, which will vote on whether to recommend semuloparin on Wednesday. The FDA usually follows panel recommendations, although it is not required to, and will make a final decision later.
Sanofi has said cancer patients getting chemotherapy have a 6.5 times higher risk of getting blood clots than patients without cancer.
But the FDA staff said data showed the rate was still very low, as only 3.4 percent of people who took a placebo during the clinical trial had a blood clot.
At the same time, about 5 percent of patients died from other causes, raising doubts about the importance of preventing blood clots in cancer patients.
Semuloparin was also tied to a higher risk of bleeding compared with placebo, with about a fifth of patients having some bleeding issues while taking the drug, including bleeding into a critical area or organ.
Shares of French drugmaker Sanofi were up about 0.1 percent at 56.26 euros on the Paris stock exchange, compared with a 0.6 percent fall in the CAC 40 Index.