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False-positive findings rife in some types of cancer screening.

CHICAGO -- Screening for colorectal, lung, ovarian, and prostate cancer resulted in false-positive findings in almost half of 68,415 adults who underwent cancer screening in a major clinical trial.

If unnecessary diagnostic procedures are performed based on false-positive findings, "substantial risk can be associated with a multiple-modality periodic cancer screening regimen," Dr. Jennifer H. Miller said at the annual meeting of the American Society of Clinical Oncology.

Dr. Miller and her colleagues in the Cancer Screening Trial Group of the National Institutes of Health, Bethesda, Md., analyzed data collected during a 3-year period from the intervention arm of the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. The study included about 157,000 adults aged 55-74 years who had no previous history of colorectal, lung, ovarian, or prostate cancer.

Men who had taken finasteride were excluded. Other exclusion criteria included death before completing all the tests and refusal to undergo all necessary tests. Those lost to complete 3-year follow-up were also excluded. After randomization, 68,415 participants were assigned to undergo screening; the others were assigned to a control arm that received usual medical care.

Men randomized to the screening arm were offered annual serum PSA tests, annual digital rectal exams, annual chest xrays, and flexible sigmoidoscopy at baseline and at 3- to 5-year intervals. Women in the screening arm were offered annual CA-125 serum tests, annual transvaginal ultrasounds, annual chest x-rays, and flexible sigmoidoscopy at baseline and at 3- to 5-year intervals. Men and women in the study were eligible for up to 14 screening tests during the study period. Results for participants in the control arm were not reported.

The authors defined a false-positive diagnosis as a positive screening test that did not lead to a cancer diagnosis within the 3-year follow-up period. Advanced adenomatous colonic polyps were considered to be true-positive results.

Almost half of the participants (29,152) had at least one false-positive test (42.6%). The cumulative risk of a false-positive test increased with the number of tests performed, and was higher in men than in women. After one test, the risk was 5.7% for men and 2.2% for women.

The authors used Kaplan-Meier curves to determine that after receiving up to 14 tests, the risk of having at least one false-positive result was 60% for men and 49% for women. The cumulative risk of a diagnostic procedure resulting from a false-positive screening test was 29% for men and 14% for women.

One test resulted in more false-positive readings than any of the others. "Both men and women were more likely to have a false-positive flexible sigmoidoscopy than anything else." PSA levels also increased the overall false-positive risk in men.

Dr. Miller urged physicians to discuss false-positive risks with patients undergoing cancer screening.

Dr. Claudine Isaacs of Georgetown University, Washington, commented on the results. "Dr. Miller's study really makes us think about the impact of what we do with screening, given the high likelihood of false positives with multiple and repeated exams," she said.


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Author:Lovinger, Sarah Pressman
Publication:Internal Medicine News
Geographic Code:1USA
Date:Aug 15, 2007
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