A new genetic test can reveal the source of some mysterious cancers and lead to quicker treatment, Israeli researchers reported Sunday.

Israel-based Rosetta Genomics said its test, still not perfected, uses microRNAs, a type of genetic material that regulates genes and known to be involved in cancer. Corporate researchers used the microRNAs to identify tumors that had spread in the body from unknown sources — a type of cancer known as "cancer of unknown primary" or CUP.

Most cancers are named according to where they first develop — such as breast cancer or lung cancer or colon cancer. Even if these cancers spread, or metastasize, to the liver or brain or bones they are still identified by their primary origin.

"But there is a group of patients who have tumors that appear in a metastatic site which, with the best imaging, you can't find a primary tumor," said Dr. Martin Raber of the University of Texas M.D. Anderson Cancer Center in Houston. "It either acquired the ability to metastasize so early in development that primary didn't develop. Or the primary never existed."

CUP accounts for 2 percent to 5 percent of cancers diagnosed in the United States each year, according to the American Society of Clinical Oncology.

Being able to identify the primary origin of a cancer is key to treating it, said Raber, who did not take part in the research.

"Today we have specific chemotherapies. We have therapies for colon cancer that don't seem to work in other settings," Raber said in a telephone interview. "You can no longer design one regimen that captures all tumors."

Writing in the journal Nature Biotechnology, Nitzan Rosenfeld of Rosetta and colleagues said they used microRNAs as biomarkers to identify where in the body a tumor started. After examining 400 samples of 22 different tumor tissues and metastases, they identified the source in two-thirds of cases, they reported.

(Agencies via Xinhua News Agency March 26, 2008)