DNA Ploidy May Predict Course of Prostate Cancer

CHICAGO--DNA ploidy in needle biopsy specimens is proving to bea highly accurate method of predicting local and distant spreadof prostate cancer, as well as the probability of recurrence,Matthew Rifkin, MD, reported at the annual meeting of the RadiologicalSociety of North America.

As a result, he said, clinicians should be able to use DNA ploidyanalysis of needle biopsy specimens to tailor treatment to theaggressiveness of the cancer and avoid unnecessary surgery.

"One of the challenges when deciding how to treat canceris knowing whether or not you're dealing with a cancer that islikely to spread or recur. If prostate cancer is not likely torecur, it doesn't make much sense to subject men to surgery andits potential side effects, such as impotence or urinary incontinence,"said Dr. Rifkin, professor and chairman, Department of Radiology,Albany Medical College, New York.

A full assessment of the prostate cancer typically has had towait until a specimen of tissue was obtained at surgery becausean accurate histologic grade of the tumor could not be determinedfrom biopsy samples. The accuracy of the histologic assessmentof a biopsy specimen has been suspect because the small-gaugebiopsy needles were thought to cause fragmentation of tumor cells.

DNA information, however, is preserved in biopsy specimens, anda study by Dr. Jeffrey Ross, chairman of pathology, Albany MedicalCollege, along with Dr. Rifkin, shows that DNA analysis of needlebiopsy specimens is just as accurate as the histologic evaluationof radical prostatectomy specimens in predicting the course ofprostate cancer.

Needle biopsy specimens were obtained from nearly 100 men withprostate cancer who were followed for 4 to 5 years. The biopsyspecimens were compared with radical prostatectomy specimens forDNA ploidy analysis. Such analysis determines the extent of multiplesets of chromosomes in a sample of cells. It characterizes DNApatterns as diploid, which has the usual two sets of chromosomes,or aneuploid, which has a different number of sets of chromosomes.

Aneuploidy in either the biopsy samples or the surgical specimenswas the best indicator of the probability of cancer migrationor recurrence, Dr. Rifkin said. The rate of cancer spread beyondthe prostatic capsule or recurrent tumor was three to four timeshigher in aneuploid tumors than in diploid tumors.

Because of its high degree of accuracy, the DNA ploidy analysisof needle biopsy specimens should help physicians plan appropriatetherapy without subjecting all men to radical prostatectomy, Dr.Rifkin stressed. Physicians thus should be able to identify menwho have non-locally contained cancer that may respond betterto more conservative therapy.

The DNA analysis costs anywhere from $30 to $100 to perform ina reference laboratory. "The test will be very cost effectiveif it prevents unnecessary surgeries," Dr. Rifkin noted.