We have described previously the isolation and characterization of five distinct subpopulations of tumor cells from a single spontaneous strain BALB/cfC3H mouse mammary tumor (Cancer Res., 38: 3174–3181, 3758–3763, 1978). Subpopulations 68H and 4.10 are polygonal and grow in epithelioid patterns in vitro, whereas subpopulations 66, 67, and 168 are fusiform and grow in lattice or fibroblast-like patterns. Line 4.10 produces tumors with distinctly glandular architecture, whereas the other four subpopulations produce poorly differentiated tumors with mixed epithelial-sarcomatous histological patterns. All five lines were evaluated for epithelial characteristics. Dome formation, characteristic of transporting epithelial cells, could be induced by dexamethasone or dimethyl sulfoxide only in line 4.10 cells. Antibodies to cell type-specific mammary epithelial antigens reacted with each of the subpopulations. All five subpopulations had ultrastructural features of epithelial cells, including desmosomes (all five lines), junctional complexes (68H, 4.10, early-passage 66 and 67 only; poorly defined in 168), and growth in cords demonstrating polarity (68H cells). Less definitive myoepithelial characteristics were also seen in four of the lines, including an incomplete reaction for Na+-K+-ATPase (4.10 cells), hemidesmosome-like junctions (168 and early-passage 66 cells), and pinocytotic vesicles at lower than normal frequency (66, 67, and 168 cells). Thus, none of the lines were distinctly myoepithelial. We conclude that the five subpopulations are epithelial cells that express a spectrum of epithelial characteristics.

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This work was supported by USPHS Grants CA-27419, CA-13943, CA-23539, and CA-19455 from the NIH, American Cancer Society Grant PDT-99, an institutional grant to the Michigan Cancer Foundation from the United Foundation of Greater Detroit, and the E. Walter Albachten bequest.

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