Heterogenic properties of clonal cell lines derived from canine mammary carcinomas and sensitivity to tamoxifen and doxorubicin.

Five clonal cell lines were established from each of 3 cell lines derived from 3 primary malignant canine mammary tumors. The clonal lines in each series were compared with one another and to the respective parent cell line with regard to cellular morphology, growth on plastic, cloning efficiency (CE) and colony sizes in soft agar, estrogen and progesterone receptor (ER, PR) status, and response to tamoxifen or doxorubicin in clonogenic assays. The most remarkable differences observed among the cell lines were in CE, colony sizes, and sensitivity to doxorubicin. The clonal line which contained measurable ER, had a shift in colony-size distribution to smaller colonies when exposed to tamoxifen or tamoxifen with estradiol that may have been estrogen-receptor mediated.