DNA ploidy and cell kinetic characteristics in canine non-Hodgkin's lymphoma

Malignant lymphoma in the dog is frequently postulated and used as a therapeutic model for non-Hodgkin's lymphoma (NHL) in humans. In this study DNA ploidy and the cell kinetic characteristics of canine malignant lymphoma were studied by flow cytometric (FCM) nuclear DNA measurements on fresh frozen tumor tissue from 94 dogs with NHL and on material from non-neoplastic lymph nodes from 20 dogs. The results were correlated with histomorphology, immunophenotype and survival. All non-neoplastic tissues were diploid, whereas of the 94 lymphomas 74 were diploid or near-diploid and 20 aneuploid. Of the aneuploid lymphomas, 1 contained a hypoploid cell population. DNA-indices of the aneuploid peaks ranged from 0.87 to 1.21 (mean 1.11). The mean S-phase fraction (8.2%, SD 4.8) was significantly lower in the non-neoplastic tissues than in the lymphomas (11.4%, SD 5.1). A linear correlation was observed between FCM S-phase fractions and bromodeoxyuridine (BrdU) labeling indices (r = 0.78; p < 0.001) determined in paraffin-embedded tissue sections from 18 dogs with NHL after in vivo BrdU labeling. DNA ploidy status did not correlate to the S-phase fraction. There were no differences in S-phase fraction and DNA ploidy between B cell and T cell lymphomas or between different histological classes using the Working Formulation. No correlation was found between S-phase fraction or DNA ploidy and survival in a series of 59 dogs treated with a combination chemotherapy protocol. It is concluded that the frequency of DNA aneuploidy in canine malignant lymphoma is similar to that in human NHL. In contrast to findings in human NHL, however, no relationship was found between DNA ploidy or cell kinetic features and histomorphology or prognosis.