CSF1 and neoplasm: In addition to PTHrP, tumor cells can directly express RANKL, leading to osteolysis, and secrete other pro-osteoclastogenic factors such as macrophage colony-stimulating factor (M-CSF), Interleukin (IL)-1α, IL-6, IL-8, and prostaglandin E2, all of which further promote bone degradation and support tumor growth within the bone microenvironment [16,17,18].