CSF1R and breast cancer: Although these data suggest potential for CSF-1R inhibition, several important variables remain unresolved, including: (1) intracranial injection of tumor cells versus hematogenous metastasis assays; (2) differential responsiveness of breast cancer subtypes to CSF-1R inhibition; (3) the potency and specificity of CSF-1R inhibitors; (4) timing and frequency of drug administration; (5) endpoints of experiments (prevention, treatment of established lesions).