June 2 (Bloomberg) -- Roche Holding AG, the world's biggest maker of cancer medicines, rose the most since February in Zurich trading after new studies eased concerns that its Avastin tumor drug might lose market share to Merck KGaA's Erbitux treatment.

Roche, based in Basel, Switzerland, climbed as much as 8.1 Swiss francs, or 4.5 percent, to 187.8 francs, its biggest gain since Feb. 25. The shares traded at 187.1 francs at 1:40 p.m.

Over the weekend Roche said a trial found that Avastin helped patients with colorectal cancer that has spread live about two years longer in clinical studies. Merck released data that indicated Erbitux may not threaten Avastin's dominance of the bowel and lung cancer markets.

``We reckon Avastin in first-line metastatic colorectal cancer is not likely to suffer'' much competitive pressure from Erbitux, Vontobel equity analysts including Andrew Weiss wrote in a research note.

Merck, based in Darmstadt, Germany, dropped 3.27 euros, or 3.6 percent, to 87.09 euros in Frankfurt trading, after dropping as much as 3.8 percent, the most since January. Merck U.S. partner ImClone Systems Inc.'s shares fell 81 euro cents, or 2.9 percent, to 27.35 euros in Germany.

``Data in lung cancer suggests very limited competition to Avastin,'' said Graham Parry, an analyst at Merrill Lynch in London, in a note to clients today.

Roche said a separate test showed that increasing the dose of Avastin may boost the drug's effectiveness in slowing breast tumors.

The findings were presented at a meeting of the American Society of Clinical Oncology in Chicago. Avastin was developed by Genentech Inc., the world's second-biggest biotechnology company, in which Roche holds a majority stake. Genentech, based in South San Francisco, California, jumped 1.23 euros to 46.77 euros ($72.65) in Frankfurt after closing at $70.87 in New York Stock Exchange composite trading on May 30.

To contact the reporter on this story: Dermot Doherty in Geneva at Ddoherty9@bloomberg.net; Eva von Schaper in Munich at evonschaper@bloomberg.net.

Last Updated: June 2, 2008 07:47 EDT