Sanofi-Aventis ( SNY) might be close to making a bid for Bristol-Myers Squibb ( BMY), its marketing partner for the blood thinner Plavix, according to a report that originated in France.

A French financial newsletter said the two companies are believed to have signed a preliminary agreement last week. The report didn't have sources.

Shares of Bristol-Myers jumped 6.3% to $27.86 in premarket trading Monday, putting it above its 52-week high. Sanofi was losing 1.4% to $44.69.

Bristol-Myers, with a market cap of $51.6 billion, is less than half the size of Sanofi.

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