Experimental liver metastases in Timp-1^low mice. (A) 1 × 10⁵ ESbL-lacZ cells were injected intravenously (tail vein), and the livers were removed 8 days later. Whole-organ X-Gal–stained livers of wild-type control and Timp-1^low mice are shown (bar, 5 mm). (B) Micrometastatic cell clusters in livers of Timp-1^low mice. Numerous additional cell clusters (< 500) composed of a few cells were dispersed 8 days after inoculation among the macroscopically visible metastatic foci (arrows) in Timp-1^low mice, but were absent in wild-type animals (bar, 0.5 mm).