A new method to provide a fresh frozen prostate slice suitable for gene expression study and MR spectroscopy.

Background: Fresh frozen tissue from radical prostatectomy specimens is highly valuable material for research on gene expression and cellular metabolites. The purpose of this study was to develop a standardized method to provide a representative high quality research sample from radical prostatectomy specimens without interfering with the routine histopathological procedure.

Methods: A complete transversal slice is collected and snap-frozen before formalin fixation and routine processing of the remaining gland. The freezing preserves the original geometric shape, thus allowing subsampling of specific cell populations without thawing. RNA was extracted from 53 cylindrical subsamples (diameter 3 mm, thickness 2 mm) from 16 consecutive frozen slices. The histological pattern was evaluated by microscopy of a cryosection from sample before further analysis.

Results: Using this novel harvesting method close to 400 slices have been collected. Whenever tumor was present in both adjacent surrounding hematoxylin-eosin sections, we found cancer in 88% of the frozen slices. The extracted RNA showed very high quality with a mean RNA integrity number of 9.16 (SD 0.53). The MR spectra showed metabolic profiles containing several resonances, which deserve further evaluation as possible biomarkers for prostate cancer. After MR analysis the RNA was still highly intact with a mean RNA integrity number of 8.40 (SD 1.53), which makes it possible to correlate transcriptomic and metabolomic profiles of the extracted samples.

Conclusion: We present a safe and standardized method for procurement of a high quality fresh frozen prostate slice, suitable for gene expression analysis and MR spectroscopy.