Shares of Ventana Medical Systems, Inc. (NASDAQ: VMSI) soared more than 48 percent on Tuesday after Switzerland's Roche Holding AG initiated a $3 billion hostile bid for the company.

Roche unveiled an unsolicited offer worth $75 a share in cash, a price representing a 45 percent premium to Ventana's closing price on Monday.

Roche said it began a tender offer after being rebuffed by Ventana's chairman following several efforts to discuss a possible deal.

Shares of the company jumped $25.12, or 48.55 percent to $76.95 during the normal trading session on Tuesday.

Tucson, Ariz.-based Ventana makes systems to analyze human tissue to diagnose and treat disease. The company has 1,000 employees. Last year it had sales of $238.2 million and a net income of $31.6 million.

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