Small prostate size and high grade disease--biology or artifact?

Prior radical prostatectomy series have shown an inverse association between prostate size and high grade cancer. It has been suggested that smaller size prostates arise in a low androgen environment, enabling development of more aggressive cancer. We propose that this observation is the result of ascertainment bias driven by prostate specific antigen performance.

We identified 1,404 patients from the Stanford Radical Prostatectomy Database with clinical stage T1c (723) and T2 (681) disease who underwent surgery between 1988 and 2002, and underwent detailed morphometric mapping by a single pathologist. Multivariate linear regression was performed to assess for the effects of age, prostate weight and prostate specific antigen on total and high grade (Gleason grade 4/5) cancer volume and percentage of high grade disease.

In patients who underwent biopsy due to abnormal prostate specific antigen (stage T1c), prostate weight was negatively associated (p = 0.0002) with total cancer volume, volume of high grade disease and percentage of high grade disease. For patients who underwent biopsy based on abnormal digital rectal examination (stage T2) these associations were not observed.

Improved prostate specific antigen performance for high grade disease results in ascertainment bias in patients with T1c disease. Thus, the association between prostate size and high grade disease may be a consequence of grade dependent performance of prostate specific antigen rather than true tumor biology.