Banking of fresh-frozen prostate tissue using the alternate mirror image protocol: methods, validation, and impact on the pathological prognostic parameters in radical prostatectomy

We evaluated the value of the 'alternative slices mirror image method' used in prostate tissue banking in terms of predicting the sampling of cancerous tissue while preserving the pathological prognostic information. The concordance of diagnosis between banked sections and their mirror image paraffin- sections was studied using 50 cases corresponding to 400 H&E sections taken from 400 banked frozen blocks (two presumed benign and two presumed cancer for each case). The mean number of paraffin blocks in each case was 21. On average 29% of the prostate gland was banked and banked tissue contained cancer in 47 cases (94%). There was no difference between the concordant and discordant groups in terms of the final Gleason score, pathological stage, prostate size, number of banked blocks and the percentage of the prostate submitted for banking. However, concordant cases had larger foci of cancer in the mirror image paraffin block (P = 0.0088). In addition, the surgical margins sections which are not banked using this method provided important information about the pathological stage, surgical margins status and the final Gleason score in 2.6, 2.6, and 1.3% of cases, respectively. The 'alternative slices mirror image method' is a straightforward method that is highly efficient in banking prostatic cancerous tissue. Overall, tumor volume and especially size of tumor foci in the image paraffin block are the most important factors in dictating the success rate of banking frozen cancerous tissue. Including 'surgical margins' sections for histology provides additional important prognostic information in a minority of cases.