Reduced spontaneous tumor metastasis in Src-deficient host mice. Following subcutaneous injection of D121 lung carcinoma cells and resection of primary tumors, mice were incubated for an additional 16 to 18 days. Upon harvest, lungs were weighed (A) and examined for metastatic lung tumor nodes (B) (n = 8). Error bars indicate standard error. (C) There was a significant reduction in lung tumor burden in src^–/– mice versus controls, as measured by wet lung weight (*P < .04) and tumor foci (*P < .05) (n = 8). (P values determined by 2-tailed unpaired Mann-Whitney test.) Representative stereomicrographs of lung tumor burden are shown from src^–/– or control src^+/– hosts.