Persistent gestational trophoblastic disease: DNA image cytometry and interphase cytogenetics have limited predictive value.

DNA flow cytometry has shown a wider spectrum of DNA content in the complete hydatidiform mole (CM) than the originally reported diploidy. Conflicting results have been published about the relationship of DNA content and the occurrence of persistent gestational trophoblastic disease (PGTD). In the present study, 71 cases of CM and 4 cases of partial mole accompanied by PGTD and 100 cases of CM without PGTD were evaluated with DNA image cytometry for differences in DNA-ploidy pattern, expressed as the 2.5c and 5c exceeding rates. A pilot study of 20 cases of each group was performed using interphase cytogenetics to detect differences in the frequency of numerical chromosomal aberrations and in sex chromosome composition. For this purpose, DNA probes specific for the pericentromeric regions of chromosomes 1 and X and for the long arm of chromosome Y were incubated on 6-micron paraffin tissue sections. The results showed no differences between CMs with or without PGTD; DNA polyploidy occurred in 99% and 98% of cases, respectively; the 2.5c exceeding rate and 5c exceeding rate were 62.6 and 62.4, and 6.5 and 6.0, respectively. The frequency of numerical chromosomal aberrations as detected by interphase cytogenetics was 23.4 and 22.8%. An XY pattern was found in 3 of 20 cases of CM with PGTD and in 4 of 20 cases of CM without PGTD. The four cases of partial mole showed a DNA-ploidy pattern identical to that of a CM. For this reason, they would be better reclassified as CMs, despite the presence of nucleated red blood cells or amnion. Although nuclear atypia and corresponding increased DNA content is pronounced but variable in CMs, the occurrence of PGTD is not related to variations in quantitative DNA content nor to gross heterology or homology in sex chromosomes.