CHICAGO - Freezing tumors may help relieve the extreme pain of cancer that has spread to the bone, which is often untouched by narcotics or radiation, U.S. researchers said on Tuesday.

This freezing process, called cryoablation, is often used to destroy kidney, prostate and other tumors, but researchers at the Mayo Clinic in Rochester, Minn., found it eased cancer pain in 80 percent of patients in a small study, and the effect lasted for up to six months.

About 100,000 people in the United States each year have cancer that metastasizes, or spreads, to the bones. Radiation therapy is the most common treatment for localized pain in metastatic cancer.