UPDATE 1-Sanofi dismissive of "poor quality" Lantus studies

* CEO warns against risk from "junk science"

* Sanofi to work with others to probe Lantus risks further

* Prospective randomised study not practical, takes too long

(Adds details, background)

LONDON, June 29 (Reuters) - Sanofi-Aventis (SASY.PA) Chief Executive Chris Viehbacher said on Monday that European studies highlighting a possible link between cancer and its long-acting insulin drug Lantus for diabetes were "of poor quality".

Shares in the French drugmaker have tumbled on concerns about Lantus's safety profile -- but Viehbacher told analysts in a conference call the issue had been mainly a stock market event, with the medical community far less impressed by the findings.

Scientists have discussed for more than a decade the theoretical links between the actions of insulin in the body and development of cancer, he noted.

"There are big scientific questions here that have been assessed for a number of years and to try to resolve them with a couple of quick and dirty patient registries does not do justice to the importance of these scientific questions," he said.

Sanofi plans to conduct further research to get to the bottom of the findings thrown up by the retrospective analyses of patient groups in Germany, Sweden and Britain, which the authors of the studies acknowledged were inconclusive.

A large randomised prospective study, however, would not be practical since it would take too long to produce a result, Viehbacher said. Instead, the company may collaborate with other research groups to provide a robust answer.

"If there are studies that we can do that would further reassure patients, I think we would want to do them with the scientific community in a way that isn't junk science. I think there is too much of a risk of seeing more junk science here," he said.

Investors fear patients and doctors will turn away from Lantus and switch instead to treatments that are perceived to be safer, such as Novo Nordisk's (NOVOb.CO) rival long-acting insulin Levemir.

Viehbacher, though, played down the danger. "The competitive position versus Levemir hasn't changed because of these studies," he said.

Also on Monday, the European Medicines Agency said it was asking its scientific experts to perform a detailed assessment of the European studies' results and any other relevant information, since a link between Lantus and cancer "cannot be confirmed nor excluded".

The watchdog added there was at this time no recommendation that patients should change their current treatment.

For an overview of stories on Lantus, please click on [ID:nLT76501] (Reporting by Ben Hirschler)