Sanofi may suffer, whatever final Lantus verdict

In fact, the theoretical possibility of Lantus being a mitogenic, cancer-causing compound has been around for nearly a decade, said Bernstein's Anderson, noting that U.S. Food and Drug Administration review documents dating back to 2000 mentioned findings of malignancies in rodents.

For Denmark's Novo Nordisk, whose shares fell nearly 4 percent on Friday, the issue is something of a two-edged sword, according to Sam Fazeli of Piper Jaffray.

Novo could potentially gain from problems at its rival, and it might also benefit from any shift in demand toward its short-acting insulins. But there is a risk that users will be wary of all modern insulins and there may be a more general switch to older, cheaper insulin products.

($1=.7177 Euro)

(Editing by Jon Loades-Carter)