Detection of disseminated and/or metastatic tumor cells in the new hosts. Single-cell suspensions from the lungs of mice double transgenic for PyMT and MUC1 antigen (MMT) or MUC1 transgenic (MUC1.Tg) mice at indicated ages were injected into the fat pads of mammary glands of wild type (WT) mice. Mice injected with sorted CD44+ mammary tumor cells were used as controls. Eight weeks after the inoculation, the lungs were harvested from the mice, perfused to remove the circulation cells, and then processed for clonogenic assay. (a) Colonies from lung cell cultures of each mouse were counted and are presented in the bar graph. Statistical significance among groups was compared using one-way analysis of variance. (b) Expression of estrogen receptor (ER) in some cells from colonies as shown in (a) using immunocytochemical (ICC) staining. (c) Detection of MUC1/Sca1 positive tumor cells in lung tissue cells isolated from WT mice using ICC staining. (d) Metastatic lesions in the lungs of WT mice injected with sorted CD44/Sca1+ from mammary tumors (left two panels) or lungs of MMT mice (right two panels). The lungs of recipient mice were processed for immunohistochemical (IHC) staining with anti-CD44 or anti-ER monoclonal antibodies. The red square indicates the enlarged area.