Objectives: The detection of aneuploidy in colonic mucosa by flow cytometric DNA analysis has been advocated as an indicator of high risk for ulcerative colitis (UC) patients developing colon carcinoma. To date, studies have primarily utilized fresh tissue and have had two limitations: a significant number of possible false-positive findings (aneuploidy in the absence of detectable dysplasia) that may be due to DNA degradation, and the inherent inability to perform retrospective studies. The latter has compromised the adequate assessment of flow cytometric DNA analysis for its clinical utility in UC patients. Our objective was to attempt to overcome the limitations that have been present in DNA analysis by flow cytometry.
Methods: After having established, in our laboratory, an optimal method that allowed reliable DNA analysis on paraffin-embedded mucosal biopsy specimens, we conducted three separate studies to address the above problems associated with DNA analysis with fresh colonic samples: 1) comparison of DNA analysis between fresh and paraffin-embedded colonic mucosal samples from UC patients without dysplasia, 2) correlation between morphology and DNA ploidy on paraffin-embedded tissues showing no dysplasia and various degrees of dysplasia, and 3) sequential analysis of fresh, normal colonic mucosal samples to further evaluate possible causes of false aneuploidy.
Results: We observed 1) that there is discordance in DNA ploidy between paraffin-embedded and fresh samples showing no dysplasia in that aneuploidy was found in 33/46 (72%) of fresh samples, whereas 3/40 (7.5%) were aneuploid by biopsies from the corresponding anatomic sites. 2) There is excellent correlation between dysplasia and DNA ploidy results with paraffin-embedded tissue, i.e., none of 16 samples negative for dysplasia, none of seven samples indefinite for dysplasia, and seven of eight samples positive for dysplasia were aneuploid. 3) DNA degradation produced a spurious, near-diploid aneuploid peak in a normal colonic mucosal sample when it was left in saline more than 1 hr before analysis.
Conclusions: The above-described results demonstrate that performing flow cytometric DNA analysis with formalin-fixed paraffin-embedded biopsy samples is feasible and that this technique may provide more reliable ploidy results than does the use of fresh samples, when rapid refrigeration and/or freezing of the fresh samples cannot be accomplished consistently, and will permit retrospective DNA ploidy studies assessing risk of cancer in UC patients.