The results backed the findings of a large study released on Monday, which showed Lantus did not put people at risk of cancer, heart attacks and strokes when taken over long periods.

The data were presented on Monday at the American Diabetes Association congress in Philadelphia.

Worldwide, Lantus has 80 percent of the market for long-acting, or basal, insulins used to treat diabetes and the product had sales of around 3.9 billion euros ($4.9 billion) last year, representing 12 percent of Sanofi's total sales.

Only one of the studies found a "suggestion" of a link between Lantus and a modest increase in breast cancer, but only among new insulin users, researchers said. When another methodology was adopted, no such suggestion existed.

Lantus, Sanofi's best-selling drug, has been dogged by safety concerns since 2009 when a number of studies suggested a heightened risk of cancer linked to its use, with conflicting results.

Jean-Pierre Lehner, Sanofi's chief medical officer, said the findings from the three studies would reassure doctors and patients about the safety of the drug.

Sanofi is particularly reliant on Lantus because it faces a wave of patent expirations on other blockbuster medicines.

(Reporting by Elena Berton; Editing by Dan Lalor)

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