Physicians screening African-American men for prostate cancer should use different cut-off points for a popular blood test because they will accurately detect 95% of cases in this high-risk group, according to a study published in the August 1 issue of The New England Journal of Medicine. The revised normal values for the prostate-specific antigen (PSA) test are based on a new diagnostic strategy and age-specific ranges for African-Americans, who have the world's highest prostate cancer rate.
Physicians screening African-American men for prostate cancershould use different cut-off points for a popular blood test becausethey will accurately detect 95% of cases in this high-risk group,according to a study published in the August 1 issue of The NewEngland Journal of Medicine. The revised normal values for theprostate-specific antigen (PSA) test are based on a new diagnosticstrategy and age-specific ranges for African-Americans, who havethe world's highest prostate cancer rate.
"The new values will improve our ability to find prostatecancers without searching for disease that isn't there, a riskif the cut-off points are set too low," says Dr. Judd W.Moul, LTC, MC, USA. "This is especially important for a groupwith such a high risk." Dr. Moul headed the study group,which included doctors from Walter Reed Army Medical Center, Washington,DC; the Mayo Clinic, Rochester, Minnesota; and the Uniformed ServicesUniversity of the Health Sciences, Bethesda, Maryland.
Previous studies had established that African-American prostatecancer patients have higher PSA values than Caucasians at allages, and that they tend to be diagnosed with the disease at alater stage, when there is less chance for a cure. The situationhas been difficult to remedy, however, because doctors have lackeda reliable set of normal PSA values for African-Americans.
To establish accurate normal PSA values, the researchers determinedserum PSA levels for 3,475 men without clinical evidence of prostatecancer (1,802 Caucasians, 1,673 African-Americans) and 1,783 menwith the disease (1,372 Caucasians, 411 African-Americans) andanalyzed the results with respect to age and race. The analysisfound that normal PSA values were significantly higher for African-Americansthan for Caucasians. It also confirmed serum PSA as a valid screeningtool for prostate cancer.
The doctors found that the traditional age-adjusted referenceranges continued to work well when applied to white men olderthan 40 years. But the first set of age-adjusted reference rangesthey derived for African-Americans would miss 41% of prostatecancers in these men; this was clearly unacceptable.
Sensitivity-Based Test Developed for African-Americans
The problem was that the traditional strategy was designed toensure that 95% of men who had normal PSA results did not haveprostate cancer--that is, that the test was 95% specific. Thehigher the specificity of a screening test, the lower is its abilityto detect all cases of a disease--its sensitivity. For African-Americans,a PSA test based on 95% specificity had a sensitivity that wastoo low. So, using their new PSA data, the researchers developeda sensitivity-based strategy for African-Americans that wouldcatch 95% of prostate cancers without sending too many healthymen for biopsies.
According to this strategy, the normal PSA ranges for African-Americansare: 0 to 2.0 ng/mL for men in their 40s; 0 to 4.0 ng/mL for thosein their 50s; 0 to 4.5 ng/mL for those in their 60s; and 0 to5.5 ng/mL for those 70 years or older. The corresponding specificityrates for these age groups are 93%, 88%, 81%, and 78%. On a standardtest measuring how well a screening tool balances specificityand sensitivity, the new ranges scored higher than both the widelyaccepted Pap smear for cervical cancer and mammography for breastcancer.
The clinicians caution, however, that the new reference rangesshould be used only as a guide. They note that physicians shouldconsider any other risk factors a patient may have for prostatecancer, as well as his age and life expectancy, any conditionsthat affect his general health, and, more importantly, his desireto undergo further evaluation to confirm the presence of prostatecancer. The decision to proceed with diagnostic testing shouldbe made jointly by the patient and physician.
Prostate Cancer Survival
Prostate cancer is the most common cancer in men in this countryand the second leading cause of cancer death, according to theAmerican Cancer Society (ACS). Some 317,100 new cases will bediagnosed in 1996, and 41,400 men will die of the disease thisyear.
Among men treated for prostate cancer diagnosed at an early stage,ACS statistics show a 5-year survival rate of 98%. However, researchhas shown that this rate does not apply equally to African-Americansand Caucasians. Some men, for example, are thought highly likelyto have curable cancers because presurgical examination indicatesthat their tumor is confined to the prostate. At surgery, however,more than 70% of African-Americans in this category, as comparedwith 30% to 40% of Caucasians, are found to have cancer cellsescaping the margins of the gland, indicating that their diseaseis, in fact, more advanced.
"We hope our study will help raise doctors' awareness ofthe special need to diagnose prostate cancer as early as possiblein African-Americans and will give them the tools to approachthis goal," says Dr. Moul. He and his research team workas part of the Department of Defense Center for Prostate DiseaseResearch, a congressionally mandated program to study prostatecancer in the tri-service military health-care system. The programis administered by the Henry M. Jackson Foundation for the Advancementof Military Medicine in Rockville, Maryland.