Comparison of DNA and karyotype ploidy in malignant mesothelioma

The correlation between flow cytometric analysis and classical karyotyping was examined in malignant mesothelioma. Flow cytometry was used to determine the DNA ploidy mainly from paraffin blocks of 31 mesotheliomas, of which the S-phase fraction (SPF) could be defined in 17 tumors. Chromosomal results were available from 27 of these tumors. For the comparisons, both the modal (the most common) and the mean (the average) chromosome numbers were determined. A significant correlation was observed between ploidy pattern, i.e., DNA indexes and modal as well as mean chromosome numbers (p = 0.004 and p = 0.006, respectively). Otherwise the comparison between the mean chromosome numbers and DNA index proved more relevant. Although the majority of the tumors (16 of 27) had a normal modal chromosome number of 46, only 5 tumors had a normal mean chromosome number, and the remaining 22 had an abnormal number, reflecting the divergent chromosomal abnormalities. Furthermore, comparison of SPF with mean chromosome numbers disclosed a parabolic relationship; i.e., when mean chromosome number corresponded to diploid, near-diploid, or near-tetraploid cell, SPF was low, but SPF was at the maximum when mean chromosome number ranged between 60 and 63. Because SPF is an indicator of cell proliferation, this might suggest that the number of chromosomes as such also corresponds with the growth characteristics of malignant mesothelioma.