Confirmation that CSF-1-dependent macrophages promote tumor progression, particularly to invasion and metastasis, was provided by an experimental model in which the CSF-1-deficient osteopetrotic mouse was crossed with the polyoma middle T (PyMT) mouse, an autochthonous model of breast cancer to produce CSF-1-deficient PyMT mice. The gene discussed is CSF1; the disease is breast cancer.