Purpose
Even when a screening study has demonstrated a mortality reduction, the degree of pre-testing and contamination is of importance as it can dilute the “true” effect of screening. Our object was to describe the level of pre-testing and contamination in the Göteborg-1 prostate cancer (PC) screening trial.
Materials and Methods
20,000 men, 50-64 years, were invited in 1994 and randomized to either a screening group (SG) (offered prostate-specific antigen (PSA) testing every 2 yrs) or to a control group (CG). Follow-up through December 31, 2014. Outcome measurement was overall testing in the SG and CG. A positive PSA test was defined as a PSA ≥3 ng/mL.
Results
In the study, 4.2% in the SG and 4.6% men in the CG were tested before study start. During follow-up, 72% in the CG took at least one PSA test (contamination) compared to 87% of men in the SG. Of all PSAs, 24% in the SG and 39% in the CG were above threshold. In total, 66% of the men underwent prostate biopsy within 12 months from a raised PSA in the SG and 28% in the CG.
Conclusions
Similar proportions of men were PSA-tested in both the SG and CG, yet only a minority of contamination PSAs led to biopsy. Also, men in the SG started screening at a younger age. These could both be explanations for our result that organized screening is more effective in reducing prostate cancer mortality than non-organized testing. When carried out properly and compared to an unscreened population, the effects of organized screening are likely even greater than previously shown in the Göteborg screening trial.