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New imaging method shows whether treatment for advanced prostate cancer is working

April 16, 2007

Measuring diffusion of water in tissue indicates early on if tumors shrink

ANN ARBOR, Mich. — Researchers at the University of Michigan Comprehensive Cancer Center have identified a new imaging technique that can measure the effectiveness of treatment for prostate cancer that has spread to the bones. The technique involves measuring diffusion of water within tumors.

"Currently, we have no way of detecting bone tumor response to therapy, even with all of the imaging options we have available. The magnitude of this problem is huge - as many as 500,000 people in the United States have metastatic breast or prostate cancer to the bone," says study author Brian D. Ross, Ph.D., professor of radiology and biological chemistry at the U-M Medical School and co-director of the Molecular Imaging Program at the U-M Comprehensive Cancer Center.

Results of the study, which was done in mice, appear in the April 15 issue of Cancer Research.

The imaging technique, called a functional diffusion map, uses a magnetic resonance imaging scan and special software to track the diffusion, or movement, of water through the cells. Researchers mapped the changes in diffusion over the course of treatment. The tumor cells slow the movement of water, so as those cells die, water diffusion increases.

Researchers studied metastatic prostate cancer in mice; half the mice were given chemotherapy to treat the cancer, which was in the bones, while the remaining mice served as an untreated control group. Researchers performed an MRI of bone tumors to collect diffusion data. A functional diffusion map analysis found the mice that did not receive treatment had little or no change in water diffusion, while the treated mice had progressively increasing changes in the functional diffusion map over the three weeks of treatment. Researchers could identify a statistically significant change in diffusion as early as seven days after treatment began.

At the end of the study, the researchers removed the tumors and found the functional diffusion map predicted the tumors' response to treatment. Tumors or portions of a tumor that had appeared not to change on the functional diffusion map had not responded to treatment. At the same time, the map accurately predicted which cells were responsive to the chemotherapy.

"The functional diffusion map could serve as an early biomarker indicating that a tumor is responding to treatment. This could allow patients to switch to an alternative therapy without wasting time on a treatment that is not working," says study author Kenneth Pienta, M.D., professor of internal medicine and urology and director of the Urologic Oncology Program at the U-M Comprehensive Cancer Center.

The American Cancer Society estimates 218,890 men will be diagnosed with prostate cancer this year and 27,050 will die from the disease.

Ross and his colleagues have previously studied the functional diffusion map in people with brain tumors and have found the test can identify after only three weeks of treatment - more than two months earlier than traditional tests — which patients are responding to chemotherapy or radiation.

University of Michigan Health System