DNA ploidy in cell nuclei from paraffin-embedded material--comparison of results from two laboratories

In 49 pairs of contiguous sections from paraffin-embedded prostatic cancer tissue, the DNA indices (DIs) were determined by flow cytometry (FCM) at 2 different laboratories. In 3 of 45 pairs of evaluable nuclear suspensions, DIs of 1.1 (DNA aneuploid) were found at Laboratory 1, whereas all 3 tumours were classified as DNA diploid at Laboratory 2. In the remaining 42 specimens, the correlation between the DIs was excellent, though the application of strictly defined DNA ploidy ranges led to different DNA ploidy allocation in 3 cases. It is concluded that in 85-90% of the cases, reliable DIs can be obtained by FCM done in paraffin-embedded material at different laboratories. Slight technical variations and interpretation differences may lead to different ploidy allocation in 10-15% of the cases.