Enzymatic treatments on paraffin blocks for DNA flow cytometry

The Hedley method for DNA ploidy analysis on paraffin-embedded tissue allows retrospective studies of large numbers of common and rare tumors for which treatment, progression, and outcome are known. However, the technique is cumbersome and has many variables, only some of which can be controlled at the time of laboratory analysis. We performed DNA ploidy analyses on two blocks from two islet cell tumors and on five blocks from two colon carcinomas. Sections of 50-microns thickness were deparaffinized in xylene, rehydrated in graded alcohols and in distilled water, and disaggregated with various enzymatic treatments: 0.05% pepsin (30 and 90 min), 0.5% pepsin (30 and 90 min), 0.05% protease (60 min), and 0.1% protease (60 min). The cell suspensions obtained were filtered, washed in PBS, and visually evaluated in a hemocytometer. Nuclei were treated with RNAse (0.1%) and stained with 50 micrograms/ml propidium iodide. Results were evaluated with the following criteria: (a) recovery of DNA aneuploid and/or G2M cells (cell-cycle analysis and visual evaluation); (b) coefficient of variation of the major peak (DNA diploid or DNA aneuploid depending on the case); (c) amount of debris (background events and visual evaluation); (d) mean channel for the G0G1 peak; (e) event rate; and (f) G2M/G0G1 ratio. The best results were observed with 0.05% protease when there was tissue necrosis and hence cell fragility, with 0.1% protease when there was significant tissue fibrosis, and with 0.05% pepsin (90 min) when there were intact cellular specimens without fibrous entrapment. The original procedure using 0.5% pepsin for 30 min produced less cell recovery, and histogram quality similar to or worse than these modifications in all cases studied.(ABSTRACT TRUNCATED AT 250 WORDS)