Study Casts Further Doubt on PSA for Cancer Screening


In terms of likelihood ratios, PSA didn't attain numbers needed for a screening test

27 sept 2009-- Based on likelihood ratios, prostate specific antigen (PSA) concentrations at any cutoff value didn't meet the criteria needed for a screening test, according to research published online Sept. 24 in BMJ.

Benny Holmstrom, M.D., of Umea University in Sweden, and colleagues analyzed data from 540 cases of prostate cancer and 1,034 matched controls drawn from a longitudinal cohort study. Blood samples were taken from cases an average of 7.1 years before diagnosis. The researchers assessed the likelihood ratios of PSA concentrations in predicting later cancer diagnosis. A positive likelihood ratio above 10 is considered strong evidence for ruling in disease, and a negative likelihood ratio below 0.1 is thought to be sufficient for ruling out disease.

The researchers found that, at PSA cutoff values of 3, 4 and 5 ng/mL, the positive likelihood ratios were 4.5, 5.5 and 6.4, respectively. Negative likelihood ratios were 0.47, 0.61 and 0.70, respectively. However, the authors note that concentrations below 1.0 almost completely ruled out a later diagnosis of cancer, suggesting that this cutoff might help identify men with very low risk.

"Converting sensitivity and specificity into likelihood ratios would help clinicians to evaluate how effective the test might be in ruling in or ruling out the disease. Clinicians should consider using likelihood ratios together with a patient's individual risk factors for the disease to explain the potential benefits and harms of the PSA test, allowing patients to contribute to decisions," write the authors of an accompanying editorial.

The editorial authors are members of the Cochrane Prostatic Diseases and Urologic Cancers Group.

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