French drug maker Sanofi-Aventis's (SAN.FR) future growth could be adversely affected by lingering questions about the safety of its key diabetes product Lantus, analysts said Monday as many issued downgrades of the company's stock.

A series of rating cuts and slashed target prices followed the publication late Friday of studies by the European Association for the Study of Diabetes journal Diabetologia. The association, known as the EASD, called for further research into the possible link between Lantus and an increased risk of cancer.

Although the data was inconclusive, analysts say the negative publicity generated could weigh on sales of a product that Sanofi is relying on to offset declining sales of products, such as anti-clotting drugs Plavix and Lovenox, that could soon face generic competition.

"Even though the results of the publication on a link between Lantus and cancer are not clear-cut ... investors will likely remain cautious until more data are published," said Exane BNP Paribas in a research note, after downgrading the shares to neutral from outperform.

Societe Generale lowered forecasts for Lantus sales to reflect no growth in the second half of 2009, and mid-single digit growth percentage-wise from 2010. Annual sales of the drug in 2012 could be EUR3.4 billion, Societe Generale estimated, compared to the company's guidance in February of EUR5 billion that year. Societe Generale rates Sanofi shares buy.

After seeing its shares slide two days in a row amid worries about Lantus, Sanofi late Friday issued a press release saying results of the studies "clearly show that no definitive conclusions can be drawn regarding a possible causal relationship between Lantus use and the occurrence of malignancies."

Sanofi shares seemed to steady Monday and at 1035 GMT stood slightly above their Friday close a higher Paris market, trading up 0.2% or EUR0.06 at EUR40.91. The company's shares fell around 8% on Friday, after the Lantus safety issue was brought up by UBS equity research teams on Thursday. In the note, UBS analyst Gbola Amusa concluded that safety risks linked to Lantus are only theoretical but that his discussions with doctors had revealed a "number of long-established safety concerns, in particular that Lantus use may promote cancer." UBS rates Sanofi sell.

UBS estimates that Lantus will account for almost 20% of the company's annual sales by 2013.

Shares in rival drugs maker Novo Nordisk A/S (NOVO-B.KO) rose almost 6% Monday after the Copenhagen-based company moved to distance itself from the Lantus scare.

The Danish drugmaker said it has not seen any cancer risks for three of its diabetes drugs.

Novo's shares had fallen as much as 4% on Friday.

Company Web site: www.sanofi-aventis.com

By Mimosa Spencer, Dow Jones Newswires; +33 1 40 17 17 73; mimosa.spencer@dowjones.com

(Gustav Sandstrom in Stockholm contributed to this item)