CSF1R and neoplasm: Confirmation that HCK is the primary SFK transducing the CSF-1R motility signal in macrophages was provided by the observation that macrophages expressing constitutively active HCK move faster, digest matrix more efficiently and encourage greater tumor cell invasion in vitro than control macrophages while a HCK selective inhibitor, RK20449, blocks motility, degradation and invasion of both control and constitutively active HCK macrophages (72).