Flow cytometric analysis of DNA ploidy in canine mammary tumors.

DNA ploidy has been determined using flow cytometry in 23 nonmalignant and 34 malignant (primary and metastatic) mammary tumors from 46 dogs. This parameter was compared with clinical stage, histology, and estrogen and progesterone receptor analysis. Twenty-one of 34 cancers (61.8%) from 32 dogs were DNA aneuploid. Aneuploidy was also found in 4 of 23 nonmalignant tumors (17.4%) from 20 dogs. Regional lymph nodes were involved in 6 of 10 diploid and 3 of 9 aneuploid cancers of dogs with operable disease. The aneuploidy incidence was higher in dogs that had distant metastasis at initial diagnosis (8 of 11) than in those presented with local or locoregional disease (9 of 19), although this difference was not statistically significant. DNA aneuploidy incidence was not found to be related to histological tumor type, histological malignancy grade, nuclear grade, or steroid receptor presence. Heterogeneity in DNA content was found in 4 of 32 cancers (30 dogs) in samples from primary or locally recurrent lesions. In 3 of 16 cancers that were analyzed both at the primary and at secondary sites of growth, a significant variation in DNA content was observed. The degree of aneuploidy in the dog cancers was much lower than seen for human breast carcinomas with a relatively high frequency of hypoploid stemlines (7 of 34 cancers, 20.6%). The frequency distribution of DNA indices in dog mammary cancers indicates that aneuploidy evolution probably differs from that of human breast cancer.