While previous studies indicated that CSF-1R and CSF-1 are expressed in breast cancer cell lines and tumors and demonstrated the relevance of CSF-1/CSF-1R signaling in the invasiveness of breast cancer cells [26]–[31], few studies have focused on the biological role of CSF-1/CSF-1R signaling in the proliferation of breast cancer cells. The gene discussed is CSF1; the disease is breast cancer.