Introduction

1. No. 009 Trans Rectal Ultrasound (TRUS) Guided Biopsy of Prostate: Pathological analysis of cores and its clinical significance. Thomson R, Travis DDepartment of Urology, Western Hospital Footscray, Melbourne, Australia Introduction The purpose of a prostate biopsy is to identify whether a patient has cancer, how much cancer they have, and what type of cancer it is – eg. aggressive, poor prognosis. This forms a major part of the decision making process for treatment of prostate cancer, including whether a patient is offered surgery, radiotherapy or observation. Results An average biopsy core is a circular cylinder with: length 15mm, and diameter 0.6mm. The volume of the core is 15x0.6x0.6 = 5.4mm3. The volume of specimen analysed is (15x0.6x0.004)x3x3 = 0.324mm3. The percentage of the core analysed is 0.324/ 5.4= 0.06, Therefore 6% of the core is viewed by the pathologist. In a 40cc prostate the % prostate sampled is (0.324x12 cores)/40000=0.0000972 volume sample/volume prostate. In this case 0.00972% of the prostate is sampled. Aim The objective of this study was to identify the percentage of a prostate biopsy which is analysed by the pathologist in comparison to the volume of the biopsy core and the whole prostate gland. Also to look at what the chance is of randomly sampling an insignificant cancer on prostate biopsy, and to compare this to random sampling in election polls. Biopsy Needles TRUS Prostate and biopsy specimens • Methods • Investigation was undertaken into how our Institute’s pathology laboratory analyses prostate biopsy cores. • Volume of the specimen analysed in comparison to the whole core and the whole prostate gland was calculated mathematically. • Comparison was made of these percentages to random population sampling for polls. • The criteria used for insignificant Prostate Cancer based on pathologic assessment of radical prostatectomy specimens: • (1) Gleason score ≤6 without Gleason pattern 4 or 5, • (2) organ-confined disease, and • (3) tumour volume < 0.5 cm3 • It is known that a small volume (0.5 cc) of low grade cancer may have no potential for progression (clinically insignificant). • The probability of one of 12 biopsy cores hitting a 0.5cc tumour in a 40cc gland was calculated mathematically. • Voting polls: • Avoting survey involves 1,146 interviews among Australian adult voters (pop 15 million) • The maximum margin of sampling error +/- 3% points • Therefore this sample is 1146/15000000 x100 = 0.00764% (adult population). • Assuming prostate volume 4000mm3, insignificant cancer 500mm3, • and biopsy needle volume 5.4mm3 X 12 = 64.8mm3. • Calculation of probability of finding insignificant cancer < 0.5cc: • Prostate radius R1 Cancer radius R0 • Volume of cylinder (biopsy) = πR02 2(R1-R0) • Volume of sphere with center of cancer 4/3π(R1-R0)3 • Therefore Probability= • 2πR02(R1-R0) • 4/3π(R1-R0)3 • 3/2 (R0/R1)2 x1/(1-R0/R1)2 =0.137 Conclusions The prostate biopsy is a very small sample associated with false negatives. The distinction between clinically significant and insignificant cancer cannot be made on a biopsy. Biopsy sampling is comparable to random newspaper voter polls. References Noguchi M, Stamey TA et al. Relationship between systematic biopsies and histological features of 222 radical prostatectomy specimens: lack of prediction of tumour significance for men with non palpable prostate cancer. J Urol 2001 Jul;166(1): 104-9 Ploussard, G et al. The contemporary concept of significant versus insignificant prostate cancer. European Urology, 2011 Aug Vol 60, Issue 2. Van der Kwast, T et al. Guidelines for processing and reporting of prostatic needle biopsies. J Clin. Pathol. 2003; 56; 336-340 Acknowledgements Thanks to Professor S. B. Gabriel Poster presentation sponsor