Tissue shrinkage after fixation with formalin injection of prostatectomy specimens.

Prostate cancer volume correlates with stage, grade, and progression after prostatectomy. When tumor volume is measured planimetrically, results are multiplied by a correction factor to compensate for tissue shrinkage caused by processing. Injection of formalin into prostatectomy specimens was suggested for improved fixation. Our aim was to investigate how this affects the prostate volume. We studied 142 radical prostatectomy specimens. All prostates were immersed in 10% formalin. In 84 prostates (59%) we also injected 20 ml of formalin before routine fixation. The prostates were weighed unfixed after injection and after final fixation. The specimens were sliced and totally embedded. The transverse diameters of the prostates were measured on unfixed specimens and microscopic sections. The average weight loss after final fixation was 5.8 and 8.6% for formalin-injected specimens and standard-fixed specimens, respectively (p<0.001). However, when total shrinkage was estimated from the transverse diameters, there was no difference related to fixation technique (p=0.59). The average linear shrinkage was 4.5%, corresponding to a volume correction factor of 1.15. We conclude that formalin injection for fixation of prostate tissue does not influence tumor volume calculation compared to conventional fixation.