Flow cytometric DNA and cytogenetic studies in human tumors: a comparison and discussion of the differences in modal values obtained by the two methods.

The numerical chromosome values in 53 human tumors were determined and compared with the modal DNA values as measured by flow cytometry. In tumors with chromosome counts in the diploid and tetraploid range, the modal DNA values were found to correspond to the modal values based on the chromosome counts. In tumors with chromosome counts in the triploid range, however, the modal DNA values were about 15% higher than expected. In order to explain this difference, the ratio between large and small chromosomes in the karyotyped metaphases was assessed. In addition, the DNA content of individual chromosomes, including markers and minutes, was calculated as a reflection of the DNA content of the whole cell. The ratio of large to small chromosomes did not deviate from the normal ratio found in cells with diploid, triploid, and tetraploid chromosome counts. Neither difficulties in karyotyping nor short-comings in the flow cytometric methodology could be used to explain the discrepancy between the expected and empirical modal DNA values. Some of the chromosomes in triploid tumors may, therefore, contain an increased amount of DNA.