Reduction of lung metastasis by NF-κB in macrophages is an early event. IKFM or DNFM mice and controls were treated with doxycycline (dox; 2 g/L) for one week prior to cell injection. Dox treatment ended two days post cell injection and mice were sacrificed at two weeks post cells (PyVT R221A) or five weeks post cells (PYG 129). (a) Lung tumor counts in IKFM injected with PyVT R221A cells (P < 0.0001; n = 10 control, n = 7 IKFM) and representative lung images. (b) Lung tumor counts in IKFM injected with PYG 129 cells (P = 0.0270; n = 9 control, n = 8 IKFM). (c) Lung tumor counts in DNFM injected with PyVT R221A cells (P = 0.0039; n = 6 control, n = 9 DNFM).