Lung metastases from the tumor-initiating assays. (a) Representative images of lungs from tumor-bearing non-obese diabetic/severe combined immunodeficiency disease (NOD/SCID) mice are shown (n = 6). A higher magnification of lung metastases derived from orthotopic injection of 5 × 105 MDA-MB 231 or MDA-MB 231 F3 cells is shown in the lower right corner. (b) Quantitative analysis of the metastatic tumor burden in the lung. Images of lungs were taken using a digital microscope camera. Images were imported into the National Institutes of Health ImageJ software for quantitative analysis. The sum of metastatic tumor volume was first calculated from four lobes of lungs per animal (see Materials and methods), and the lung metastasis per group is presented as tumor volume (cubic millimeters). The number of animals used per group is listed in Table 1.