With its efforts to negotiate a friendly merger deal with Ventana Medical Systems rebuffed, Swiss pharmaceuticals giant Roche has announced a hostile tender offer to acquire its target for about $3 billion at $75 per share in cash.

Ventana has advised shareholders to defer taking any action on Roche's offer and said in its website, "…the company's Board will review and consider Roche's offer and, following the commencement of the tender offer, will make a recommendation to shareholders within 10 business days." Without giving any further information.

With a majority stake in Genentech, Roche already has a strong position in biotechnology. Acquiring Ventana would help it build on its diagnostics presence, where it currently has in-vitro, molecular and clinical chemistry diagnostic products.

The acquisition would also give it access to technology that helps researchers and doctors better select the right drugs for individual patients - an emerging concept known as personalised medicine

Proponents of personalised medicine say it could reduce the costs and risks of developing drugs.

"By combining both companies' expertises in in-vitro diagnostics, cancer and virology, Roche and Ventana are able to enhance their positions in the area of personalised healthcare," Roche said in its website.

Roche's offer of $75 per share in cash represents a 45 per cent premium to Ventana's closing stock price of $51.74 on Monday on Nasdaq. Its shares were suspended from trading after the announcement and when trading resumed, they jumped 52 per cent to $78.75, above Roche's proposed offer, indicating that investors expected the Swiss giant to improve its price.

Acquiring Ventana, which last year had sales of $238.2 million will dilute Roche's share capital by about 1 per cent and will first add to earnings in two to three years.

Roche said it had made several attempts to talk to Ventana about a deal, and it remains open to negotiating a friendly takeover. It also said that the tender offer remains subject to Ventana pulling its "poison pill" defence or shareholder rights plan, which would make an unsolicited acquisition costly and difficult.

The current cost of new drug development and the risks of failures in trials could be reduced if diagnostic technology identifies patients with the best chance of benefiting from a particular medicine. Similarly testing could also screen out patients who might have negative reactions to the medicine in trials.

That Roche is anxious to strengthen its diagnostics capabilities was reflected in its CEO Franz Humer's response to a conference call query, "It's vital that we build on our leading global diagnostics position either organically or through purchases."

The company also said that the proposed Ventana acquisition was just one in a string of deals aimed at boosting its diagnostics wing. Earlier this month it announced a $272.5-million purchase of US genetics analysis specialist NimbleGen Systems Inc.

Ventana has six subsidiaries that all operate under the Ventana Medical Systems umbrella. These include Ventana Medical Systems, GmbH, Ventana Medical Systems, Japan K.K., Ventana Medical Systems, Pty. Ltd., Ventana Medical Systems, S.A. BioTek Solutions, Inc. and BioTechnology Tools, Inc.