Intratumoral regional differences of DNA ploidy of gastrointestinal stromal tumors: a flow cytometric study

Mesenchymal neoplasms of the gastrointestinal tract remain controversial in regard to both diagnostic criteria and prognostic factors. In order to investigate whether DNA ploidy in a single area of a tumor can be representative of the entire tumor, multiple samples from the same tumor were analyzed in 79 cases of gastrointestinal stromal tumors.

Forty-three male and 36 female patients, aged 11 to 80 years with stromal tumors of the GI tract were selected. Flow cytometric DNA ploidy analysis was done on tissue cut from paraffin blocks by using the modified technique of Hedley et al.

All 34 benign stromal tumors displayed a concordant diploid DNA content. Eighteen (40%) of the 45 malignant stromal tumors (13 low-grade, 5 high-grade) were diploid. Aneuploid and polyploid DNA stemlines were found in 10 cases (43.4%) of low-grade stromal tumors, and in 17 cases (77.2%) of high-grade stromal tumors. DNA polyploidy was identified in 21 (46.7%) of 45 malignant stromal tumors. Also, aneuploid populations were accompanied by diploid populations.

DNA content correlated well with histologic category. Tumor aneuploidy was more frequently seen in tumors of advanced stage, but no relationship was seen between tumor stage and the presence of tumor heterogeneity. Differences in ploidy levels were thus not necessarily associated with apparent differences in histologic patterns. The mechanism responsible for regional differences in DNA ploidy in the same tumor remain unexplained. Several hypotheses are reviewed.