The difference in DNA ploidy pattern between some canine and human neoplasms appears to be genuine and a reflection of dissimilarities in DNA aneuploidy evolution.

In a reaction to the article by Deitch et al, (Anticancer Res 13: 2117-2118, 1993) evidence is presented that flow cytometrically detected DNA-hypodiploidy in canine neoplasms is genuine and not an artefact caused by autolysis or chemotherapy. Intervals between removal of tumors and freezing in our studies were much shorter (average 15 min, maximum 30 min) than e.g. for human breast tumors in which the percentage of hypodiploidy is about 2%. Also average CVs for the G0, 1 peaks in our FCM analysis of canine tumors (mammary 2.27 + 0.06, n = 179); thyroid 2.57 + 0.13, n = 88) were equal to or less than those usually found in the comparable human tumors. Biological arguments in favor of the existence of genuine hypodiploid stemlines are the finding of tetraploidized subclones of the original hypodiploid clone, the reappearance of the same hypodiploid stemline in distant metastases during clinical follow up, and the isolation of a cytogenetically and flow cytometrically hypodiploid cell line from a primary canine mammary carcinoma. It is concluded that Deitch et al, incorrectly have invoked autolysis as a source of hypodiploidy in our original studies on canine neoplasms. Our evidence for interspecies differences in the evolution of aneuploidy in tumors of the same organ therefore remains unchallenged.