Sanofi drug may increase cancer risk, studies find

* European studies see possible cancer link

* More research needed as findings not conclusive

* Patients told to stay on treatment, consider options * Sanofi stands behind safety profile of Lantus

By Ben Hirschler

LONDON, June 27 (Reuters) - Sanofi-Aventis's (SASY.PA: Quote, Profile, Research) diabetes drug Lantus may increase the risk of cancer, according to European studies involving some 300,000 insulin-treated patients, prompting a call from experts for more research.

The European Association for the Study of Diabetes (EASD), which released details online of four studies from its journal Diabetologia, said they were "far from conclusive but they do indicate the need for further investigation of this issue".

The new research was released after mounting speculation that damaging data was about to be published over a cancer link with Sanofi's modern long-acting insulin analogue, sinking the the French drugmaker's share price by 12.3 percent in two days.

Lantus, which sold 2.45 billion euros ($3.41 billion) in 2008, is a key driver for Sanofi as top drugs like Plavix and Lovenox face the threat of generic competition. Analysts have been expecting sales to grow strongly for the next five years.