Marker May Improve Diagnosis of Prostate Cancer

A protein marker has been identified that is present in prostate tumor cells but is not found in normal tissue. The gene that codes for this protein, the enzyme a-methylacyl-CoA racemase (AMACR), was identified through the use of advanced DNA microarray technology by researchers at the University of Michigan Medical School (Ann Arbor, USA).

As AMACR is present only in malignant cells and is easily visible when stained, it could improve the accuracy and sensitivity of screening tests for prostate cancer, the second leading cause of cancer-related deaths in men. The new findings appear in the April 3, 2002, issue of the Journal of the American Medical Association.

"We detected high levels of AMACR protein in over 95% of more than 300 prostate tissue samples that contained localized cancer,” says Dr. Arul M. Chinnaiyan. "Equally important, we found no AMACR protein in benign prostate tissue or in tissue with non-malignant cell changes. We then evaluated the clinical utility of AMACR immunostaining on 94 prostate needle biopsies; the sensitivity and selectivity ratings were 97% and 100%.”

The accuracy and specificity of AMACR screening suggest that it may represent a major improvement over the prostate-specific antigen (PSA) test, the only diagnostic screening test currently available to physicians. "The beauty of AMACR is that it is cancer-specific and found only in malignant cells,” says Dr. Mark Rubin. "PSA cannot differentiate between cell changes caused by cancer and those caused by benign changes in the prostate. As a result, PSA tests have a high rate of false positives, which can mean repeat needle biopsies and unnecessary surgery.”

AMACR may act as a diagnostic marker for other types of cancer, too. AMACR over-expression was found also in colorectal, prostate, ovarian, breast, bladder, lung, renal cell, lymphoma and melanoma -- with the highest amounts present in colorectal and prostate cancer.




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