UPDATE 3-US FDA: Data inconclusive on Sanofi insulin risks

* Regulators continue study of possible cancer risk

* U.S. FDA started probing Lantus safety in 2009

* Drug is one of company’s top products (Adds details on drug; updates shares)

WASHINGTON, Jan 12 (Reuters) - U.S. regulators are continuing to probe whether a Sanofi-Aventis SASY.PASNY.N diabetes treatment raises cancer risk after determining that data from four studies was inconclusive.

The FDA had announced in July 2009 that it was reviewing studies suggesting an increased risk of cancer associated with Sanofi’s long-acting insulin called Lantus, one of the company’s top-selling products.

In an update released on Wednesday, the agency said it had completed a review of four published studies and found evidence of cancer risk was “inconclusive due to methodological limitations.”

The agency also looked at a five-year randomized trial comparing Lantus to another type of insulin in patients with Type 2 diabetes. That study did not support a higher rate of cancer with Lantus but also had limitations, the FDA said.

“At this time, FDA has not concluded that Lantus increases the risk of cancer. Our review is ongoing,” the agency said in a statement on its website.

Patients should not stop taking Lantus unless told to do so by a doctor, the FDA said.

Lantus is one of Sanofi’s top products. Sales of the drug are projected to hit $6.2 billion in 2014, according to Thomson Reuters consensus estimates.

Concerns about a possible link between Lantus and cancer have hit Sanofi shares in the past. The French company is particularly reliant on Lantus because it faces a wave of patent expirations on other blockbuster medicines. That big patent "cliff" is a key reason behind Sanofi's hostile bid for biotech company Genzyme Corp GENZ.O as it hunts additional sources of revenue.

The FDA said cancer cases were being studied in an ongoing Sanofi trial of Lantus called Origin. A preliminary review did not show evidence of a higher cancer risk, the FDA said. Results from the trial are expected at the end of 2011.

Sanofi plans three other studies to evaluate the cancer issue with results expected by the end of June, the FDA said.

The agency also is considering use of a Department of Veterans Affairs patient database to shed light on the concern.

Shares of Sanofi-Aventis rose 4.9 percent to close at $33.71 on the New York Stock Exchange.

The FDA posted the notice on

Reporting by Lisa Richwine; Editing by Bernard Orr and Richard Chang