Autolysis is a potential source of false aneuploid peaks in flow cytometric DNA histograms

Serial flow cytometric nuclear DNA content analyses were performed from normal human spleen, thyroid, liver, and pancreas removed from ten patients at autopsy and stored for up to 8 d without any preservative to study the effect of autolysis on DNA histograms. Fine needle aspiration biopsy (FNAB) samples were taken in diluted ethanol and tissue biopsies from the same area in formalin for embedding into paraffin at the time of autopsy and serially thereafter. Histograms obtained from samples taken within 10 h after death had a symmetrical G1 peak with a small coefficient of variance (CV) except histograms produced from paraffin-embedded pancreatic tissue, but bimodal distributions similar to those seen in aneuploid tumors were obtained from many samples stored longer than for 20 h. The DNA indices of the bimodal histograms were usually less than 1.3. The false peaks were more prominent in FNAB samples than in paraffin-embedded samples. The time of appearance of the false aneuploid peaks varied individually, and they were usually first seen in samples taken from the pancreas, followed by the liver, the thyroid and the spleen. Because neoplasms may become necrotic in vivo and fixation of fresh surgical samples may be slow and incomplete, increased DNA staining caused by autolysis may be a source of false aneuploid peaks in DNA content analysis.