* Drug keeps tumours in check longer than just chemotherapy
* More details to be announced at unnamed scientific meeting
* Development partner Onyx's shares surge 25 pct
(Adds shares, analyst comment)
FRANKFURT, July 22 (Reuters) - Bayer BAYG.DE and its development partner Onyx Pharmaceuticals ONXX.O said their cancer pill Nexavar showed promise in treating breast tumours, the second-most common form of cancer, sending Onyx shares soaring.
Nexavar, when combined with standard chemotherapy Xeloda, helped keep tumours in check for longer than in a control group of patients receiving Xeloda only, the drugmakers said in a joint statement on Wednesday, citing data from a Phase II study.
Xeloda is sold by Switzerland's Roche (ROG.VX).
Shares in Onyx, which depends entirely on Nexavar for sales, surged 25.1 percent to $35.90 at 1427 GMT. Shares in Bayer were up 2.2 percent, outperforming the European DJ Stoxx Health Care Index's .SXDP 0.7 percent rise.
Christopher Raymond, an analyst at Baird, called the results "a possible game-changer" for Onyx.
"Combining the ubiquitous use of Xeloda in advanced breast cancer with the robustness of this 200+ patient trial, we would not be surprised to see measurable off-label use once the data are presented," the analyst said in a note to investors.
The trial involved 229 women with breast tumours that had started spreading, they added.
More details would be released in an upcoming scientific meeting, they said.
Nexavar is one of Bayer's most promising drugs, along with anti-blood clotting pill Xarelto. It is sold as a liver and kidney cancer treatment in more than 70 countries and Bayer is also pursuing approvals for use against lung tumours.
The German drugmaker aims to generate worldwide sales of more than 2 billion euros ($2.84 billion) a year from the drug.
Bayer and U.S. biotech company Onyx are testing Nexavar in a further three ongoing breast cancer studies in Phase II and are working on possible trial setups for the third and last phase of testing required for regulatory approval.
(Reporting by Ludwig Burger; editing by John Stonestreet)