On Friday, I suggested that it might be best for investors to wait for solid results before trading on rumors about whether sanofi-aventis' (NYSE:SNY) insulin product, Lantus, caused cancer.

Hours later, we got hard evidence. Sort of. The results of four trials debuted in Diabetologia, the journal of The European Association for the Study of Diabetes (EASD). But questions over whether Lantus is linked to cancer remain about as clear as concrete.

Two trials showed an elevation of cancer risk for patients taking Lantus compared to human insulin, while the other two didn't show a statistical significance. The EASD's conclusion? Only more research can sort out this conundrum.

Sanofi's problem might not be the actual level of cancer risk, but how that risk is perceived by doctors and patients. The level of heart side effects for GlaxoSmithKline's (NYSE:GSK) Avandia wasn't all that clear -- and still isn't -- but the damage is done, and the drug won't make a comeback. It will take a while before we know how damaged Lantus' reputation really is.

If doctors do start abandoning Lantus, beneficiaries might include Eli Lilly (NYSE:LLY) and Novo Nordisk (NYSE:NVO), which both sell insulin products. Lilly's and Amylin Pharmaceuticals' (NASDAQ:AMLN) Byetta could also benefit. The latter drug isn't an insulin product, but it's sometimes prescribed when oral medication is insufficient to control blood sugar levels in type 2 diabetics, but before insulin is prescribed. Given the news, doctors may keep patients on Byetta a little longer, or have patients use it as an intermediate step, instead of going straight from oral medications to insulin.

It looks like investors are relieved that the data is out -- Sanofi is up about 4.5% at the moment -- but it seems prudent to be cautious here. Whether the company is a value at these prices depends upon Lantus' reputation. Rather than reading the scientific articles, investors would be better off keeping an eye on how the media plays the reports, since that will affect patients' perceptions -- and ultimately, sales.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool has a disclosure policy.