PSA Shown to Predict Progression of Prostate Cancer

CHICAGO--Proponents of the prostate-specific antigen (PSA) testhave new ammunition to support the view that the controversialscreening method accurately predicts the progression of prostatecancer and the long-term survival of patients, thus allowing moreappropriate treatment choices.

Among 317 men with localized prostate cancer who have been treatedsince 1986, there was a 75% probability of survival for 5 to 10years when the pretreatment PSA level was less than 10 ng/mL,reported Carlos A. Perez, MD, at the annual scientific meetingof the Radiological Society of North America.

"These findings correspond with other reports that suggestthat PSA tests may be the key to determining who should undergotherapy, such as surgery or radiation therapy," said Dr.Perez, director, Radiation Oncology Center, and professor of radiology,Mallinckrodt Institute/Washington University, St. Louis.

Contradicts Toronto Study Results

The findings also contradict a recent, widely reported study conductedby researchers at the University of Toronto. These investigatorsconcluded that screening for prostate cancer using the PSA testcould not be justified (JAMA 272:773-780, 1994).

The authors of the study from the University of Tor-onto foundthat screening with the PSA test would require a community tospend between $113,000 and $729,000 to gain only one additionalyear of life expectancy from early treatment of prostate cancer.PSA screening also would reduce the quality of life for many menbecause of treatment side effects.

Even in the best scenario, the Canadian scientists stated that,with PSA screening, life expectancy would increase by only 0.6days on average for a 50-year-old man and 1.7 days for a 70-year-oldman. When quality-of-life factors were considered, there was anet loss of 3 to 13 days in life expectancy.

The Canadian study was criticized at the time of its release becausemuch of the data were gathered from medical reports that had beenwritten before PSA was used as a screening tool. It also was challengedbecause the patient population lacked an adequate control group.

The results of the investigation conducted by Dr. Perez furtherrefute the conclusions of the University of Toronto researchersby demonstrating the clinical utility and cost effectiveness ofthe PSA screening test.

Dr. Perez explained that a pelvis/abdomen computed tomography(CT) scan commonly has been done before treatment for prostatecancer to detect any diffuse disease. This scan may be eliminatedfor men who have a pretreatment PSA level of 10 ng/mL or lessbecause the yield from a CT scan on such men has been less than1%, he said.

By restricting routine CT only to those men with PSA levels higherthan 10 ng/mL, at least $40 million per year may be saved in theUnited States, he said.

When the PSA test is used to identify men who may benefit fromconservative radiation therapy, oncologists may be able to successfullycontrol the spread of localized prostate cancer without subjectingpatients to the adverse side effects associated with radical prostatectomy,Dr. Perez added.

Among 963 men with prostate cancer who were treated with radiationtherapy at the Mallinckrodt Institute of Radiology between 1969and 1991, the estimated 10-year survival rate was 78% when cancerwas confined to the prostate and was not palpable on physicalexamination.

For men with prostate cancer that was localized within the prostategland but could be felt on physical examination, the 10-year survivalfollowing radiation therapy was 65%.

Fewer Side Effects After Radiation

Men with prostate cancer that had spread beyond the prostaticcapsule but had not reached the lymph nodes or pelvic structureshad a 10-year survival rate of 40% after radiation therapy.

Compared with published reports of the sequelae of prostatectomy,the men also had fewer side effects after radiation therapy. Therate of urinary incontinence was less than 2%, compared with 10%following surgery. The incidence of impotence was about 30%, comparedwith 40% for men after surgery.

"These results shed new light on the ongoing controversyabout how to predict which cancers will be the most aggressiveand about the best way to treat prostate cancer once it is detected,"Dr. Perez concluded.