TMPro expression results in a large metastatic burden even after injection of a relatively low tumor cell burden. Gross appearance of lung lobes harvested from WT (A) and TMPro mice (B) 13 days after intravenous injection of 3 × 104 LLCGFP cells. (C) This modest tumor cell inoculum resulted in essentially no pulmonary metastases in WT mice, whereas TMPro mice developed hundreds of metastatic foci. Horizontal bars represent medians.