Breast and colon cancer involve nearly 200 mutated genes, most previously unknown, that could be a target for new cancer drugs.

It's hoped that understanding the genetic blueprint of cancer will lead to better ways to diagnose, prevent and treat it.

Dr. Victor Velculescu, a professor of oncology at Johns Hopkins University's Kimmel Cancer Center and his colleagues identified 189 mutated genes, with an average of 11 per tumour, from breast and colon cancers.

"The vast majority of these genes were not known to be genetically altered in tumours and are predicted to affect a wide range of cellular functions," the researchers wrote in Friday's issue of the journal Science.

The researchers looked at 11 samples each from breast and colon tumours that were surgically removed.

They focused on breast and colon cancer given that together, the two diseases account for about 14 per cent of the 940,000 cancer deaths worldwide each year, the study's authors said.

"This groundbreaking work provides a dramatic proof of the concept that this research approach holds great promise for providing an understanding of the genomic contributions to cancer," said Dr. Elias Zerhouni, director of the U.S. National Institutes of Health.

The study's findings are among the first to come out of the institutes' Cancer Genome Atlas project, which aims to reveal the genetics of cancer.

The discovery of genetic changes in cancer has already led to the development of treatments such as the drug Herceptin for breast cancer and Gleevec for chronic myelogenous leukemia that stop cancer while minimizing harm to the patient.