Prostate cancer detection: Relationship to prostate size

Objectives. It has been suggested that the lower detection rate for cancer in large prostates is due to the smaller proportion of tissue sampled. To e xamine this hypothesis, we evaluated whole-mount radical prostatectomy spec imens in which the volume of cancer had been determined. We correlated canc er volume to overall gland volume. In addition, we performed stochastic com puter simulations of parasagittal sextant biopsies on the same group of rad ical prostatectomy specimens. We correlated the likelihood of a positive ca ncer biopsy simulation with tumor volume and gland size. Methods. Six hundred seven tumor foci from 180 serially sectioned whole-mou nt prostatectomy specimens were mapped and digitized. Tumor volume was calc ulated by a step-section planimetry algorithm. Before sectioning, each glan d was weighed. Systematic parasagittal sextant biopsies were computer simul ated for each case. For each prostate, 40 simulations were performed, with random variations in biopsy location programmed for each run. Overall cance r detection by biopsy was considered positive if 90% of the 40 simulation r uns were positive for cancer. Chi-square tests were used to evaluate statis tical significance. Results. Small-volume cancers (0.5 cc or less) were twice as frequent in la rge glands greater than 50 g (P = 0.03). These small-volume tumors comprise d 33% (13 of 40) of cancers in prostates greater than 50 g, 16% (5 of 31) i n glands less than 30 g, and 14% (15 of 109) in glands 30 to 50 g. The rate of positive sextant biopsy simulation was lower in glands greater than 50 g than in glands 50 g or less (48% versus 67%, P <0.03). Smaller cancers we re much less likely to be detected in the simulations. The simulation detec tion rate for cancers 0.5 cc or less was 18% (6 of 33), compared with a det ection rate of 73% (107 of 147) for cancers greater than 0.5 cc (P <0.00001 ). Conclusions. The observed lower cancer detection rate in large glands is a result of the higher proportion of low-volume cancers in these glands. This suggests that large prostates are more likely to be biopsied because of an elevated prostate-specific antigen value resulting from benign elements of the gland and not from a significant cancer. Increasing the number of core s solely to compensate for increased prostate size risks a disproportionate increased detection of small-volume tumors with a low clinical likelihood of progression. (C) 1999, Elsevier Science Inc. All rights reserved.