Prostate size linked to reliability of tumor grading

May 23, 2005

Men with larger prostates seem less likely than those with smaller glands to be diagnosed with high-grade cancer at biopsy. However, that size-related difference may reflect sampling artifact, as prostate volume appears not to be a significant predictor of true histologic grade, according to a retrospective study by urologists at the University of Toronto.

Men with larger prostates seem less likely than those with smaller glands to be diagnosed with high-grade cancer at biopsy. However, that size-related difference may reflect sampling artifact, as prostate volume appears not to be a significant predictor of true histologic grade, according to a retrospective study by urologists at the University of Toronto.

"Our data have implications for patient counseling and management decisions as they speak to the reliability of biopsy-derived tumor grading. They also provide an alternative explanation for the higher proportion and number of high-grade tumors found among men who took finasteride relative to placebo in the Prostate Cancer Prevention Trial. Extrapolating our data to that study suggests that the finasteride-induced reduction in prostate volume may account for its association with higher-grade tumors," said Girish Kulkarni, MD, of the University of Toronto's department of urology.

The investigation analyzed risk factors for diagnosis of a high-grade tumor (Gleason pattern ≥4) in 369 men who had undergone TRUS-guided biopsies and who went on to radical prostatectomy. TRUS volume ranged from 14.5 cc to 137.1 cc.

To investigate volume as a risk factor, data from the 369 men were divided into quartiles.

On biopsy, 192 men (52%) had high-grade tumors, with fewer such tumors among men with smaller prostates. In univariate and multivariate analyses, prostate volume was a significant predictor of biopsy-derived high-grade prostate cancer.

According to the RP results, 237 tumors (64.2%) were high-grade. Comparisons with the findings from the biopsy analyses showed a higher rate of tumor upgrading among men with larger versus smaller prostates. The 237 high-grade tumors diagnosed in the RP specimens were evenly distributed across all volume quartiles and in univariate and multivariate analyses, prostate volume was not predictive of true histologic grade.