July 12 (Bloomberg) -- Roche Holding AG, the world's biggest maker of cancer medicines, signaled it may raise its $3 billion hostile takeover bid for U.S. diagnostics maker Ventana Medical Systems Inc. after the offer was rejected yesterday.

Chief Executive Officer Franz Humer, while describing Roche's current offer as ``full and fair'' in a letter to Ventana Chairman Jack Schuler dated July 11, left open the door to a compromise.

``To the extent that you believe that Ventana has additional information that would support a valuation in excess of our offer, we would be willing to consider it in a negotiation with you,'' Humer wrote in the letter, released on Roche's Web site.

Ventana dismissed Roche's $75-a-share offer yesterday, saying it doesn't factor in new diagnostic tests the Tucson, Arizona-based company plans to introduce next year. The takeover would give Roche a test to identify patients who may respond to Herceptin, the breast-cancer treatment that is the Swiss company's No. 2 drug. Ventana shares reached $82.53 yesterday, a record until further gains today.

``I think it is possible Roche will raise once and then walk away if there is no agreement,'' said Andrew Fellows, an analyst at Helvea Ltd. in London, noting that Roche's current offer is already at a 45 percent premium to Ventana's share price before the bid was disclosed.

Shares of Basel, Switzerland-based Roche fell 30 centimes, or less than 1 percent, to 216.2 Swiss francs at the close of trading in Zurich. Ventana's stock rose $3.44, or 4.2 percent, to $85.97 at 4:30 p.m. New York time in Nasdaq Stock Market composite trading.

Poison Pill

Ventana disclosed separately in a regulatory filing today that it promoted Hany Massarany, 46, to chief operating officer on July 9 and will pay him a base salary of $330,000. Massarany, who joined the company in 1999, was in charge of global operations. No previous chief operating officer is listed for the company.

The company yesterday said Roche hadn't considered that it expanded its sales force by 20 percent each of the past three years and misgauged how much tests in development could accelerate the development and sales of cancer drugs. The company said it wouldn't negotiate with Roche, citing ``high- handed tactics.''

Roche last Friday sued Ventana and the Arizona attorney general over a state law that could derail its bid for the U.S. company. The Swiss drugmaker also sued in Wilmington, Delaware, to invalidate a ``poison pill'' defense Ventana adopted that would give its existing shareholders rights to buy new stock at half price, increasing the cost of the buyout.

Fourth Bid

If Roche wins the cases, ``we believe it will ultimately be able to take over the company albeit at a sweetened offer price,'' Vontobel equity analysts wrote in a research note today.

The bid represents the fourth this year announced by Roche, of Basel, Switzerland, of companies with screening tools that help doctors adjust treatment to a patient's genetic profile.

Roche in March agreed to buy CuraGen Corp.'s 454 Life Sciences for $140 million in cash to gain the company's DNA- mapping technology, which can help identify the genetic cause of a disease or point to ways to treat it. The following month, Roche said it would spend $600 million to acquire BioVeris Corp. and add screening technology that stimulates cells to emit light. In June, the company agreed to buy NimbleGen Systems Inc. for $272.5 million to add more genetic tools for drug research.

Governments and health insurers, trying to cut costs, are demanding that drugmakers find ways to determine which patients won't be helped by their products. Herceptin had $1.2 billion in sales last year.

To contact the reporter on this story: Dermot Doherty in Geneva at Ddoherty9@bloomberg.net

Last Updated: July 12, 2007 16:56 EDT