Background: Epidemiological studies of prostate cancer (PCA) which are based on case control comparisons may be effected by verification bias. Verification bias exists when the experimental group has verified PCA, while the control group is presumed to be cancer free, but this is not histologically verified.
Materials and methods: Review of the literature and our recent experience with case-control studies of PCA in an autopsy model.
Results: When autopsied prostates were evaluated for cancer based on prostatic specific antigen <4 ng/ml, negative biopsy or both criteria, the contamination rate was 22%, 15% or 12%, respectively. The effect of contamination by occult PCA alters the odds ratio and p-value of the results.
Conclusion: It is important to recognize that contamination of the control population by occult carcinomas reduces the reliability of the results. Rigorous characterization of the experimental and control groups is needed in order to preserve the integrity of the conclusions.