Merck KGaA's Stimuvax, an experimental cancer vaccine for use against breast cancer, is in its third and last phase of testing required for obtaining regulatory approval.

Stimuvax co-developed by Darmstadt, Germany- based Merck and U. S. bio-tech firm Oncothyreon, and in its trial dubbed STRIDE(a), to be tested on patients with advanced, inoperable breast cancer, is a so-called therapeutic vaccine, designed to trigger an immune response that helps the body kill cancer cells by itself.

Rearchers will be focusing on patients treated with hormonal therapy, with the involving over 900-patients as it also looks at overall survival, quality of life, tumour response and the safety of the drug.

Oncothyreon shares went up 17.8% to C$3.04 on the Toronto Stock Exchange Monday afternoon, after touching a high of C$3.20 earlier in the day, on hearing the news, while, shares were up 16.7% at $2.66 on the Nasdaq.

Late last year, the small biotechnology company after changing its name from Biomira, moved to the United States from Canada.

Breast cancer, the second most common form of cancer after lung cancer, is the leading cause of cancer deaths in women, and the drug, also being tested against non-small cell lung cancer in Phase III, has been seen to prime the body's immune system for detecting and attacking cancer cells.

Merck in competition with other biotech firms like Transgene, Dendreon Corp. and Antigenics, is racing to bring cancer vaccines to market.

While, Transgene's TG4010 compound also targets lung tumours, the most common form of cancer, the Dendreon and Antigenics drugs are aimed at prostate cancer and brain cancer, respectively.

Merck also plans to request regulatory approval for Stimuvax in lung cancer in 2012, as with the drug inducing the immune system to fight cancer cells that contain a gene called MUC-1, the first real tumour vaccine.