TM^Pro mice exhibit a profoundly prometastatic phenotype relative to WT mice. Gross appearance of representative single lung lobes harvested from a WT (A) and TM^Pro mouse (B) 13 days after IV injection of 3 × 10⁵ LLC^GFP cells viewed under a fluorescence stereoscope. Note the overwhelming amount of GFP⁺ tumor tissue in the TM^Pro lung lobe in panel B relative to the WT animal in panel A. H&E stained sections of lung tissue revealed small, discreet metastatic foci (arrowhead) in lungs from WT mice (C), whereas lungs harvested from TM^Pro mice were largely effaced by tumor tissue (D). (E) Consistent with the apparent increase in tumor burden, the weight of lung tissue harvested from LLC^GFP-challenged TM^Pro mice was significantly greater than that of lungs harvested from LLC^GFP-challenged WT mice, or lungs from tumor-free animals. Similar findings were observed in cohorts of WT and TM^Pro mice intravenously injected in parallel with B16 melanoma cells. Shown are representative whole lungs from WT (F) and TM^Pro mice (G) as well as H&E-stained sections of lung tissue from WT (H) and TM^Pro mice (I). (J) Also paralleling results with LLC cells, the weight of lungs harvested from B16-challenged TM^Pro mice was significantly greater than that of lungs harvested from B16-challeged WT mice or tumor-free animals. Size bars represent 200 μm (C-D,H-I) or 250 mm (F-G). Data represents mean and SEM, *P < .005.