CSF1R and neoplasm: During tumor development both F4/80 and CSF1R positive cells within the tumors significantly increased after Regorafenib administration (Fig. 4c–f; see F4/80 and CSF1R staining of the total pancreas in Supplementary Fig. S9A), indicating that infiltration of macrophages with a tumor-promoting phenotype as potential compensatory mechanism conferring therapy resistance.