SIRPA and neoplasm: We next examined whether the Elk-1/Sirpα axis in macrophages regulates phagocytosis and CRC progression because Sirpα functions as an inhibitory checkpoint molecule in tumor phagocytosis.16 In vitro phagocytosis assays showed that Elk-1 transgene expression in macrophages notably inhibited the phagocytosis of MC-38 cells and CT-26 cells by macrophages, whereas the blockade of Sirpα with antibodies prevented this activity (Fig. 3a–c).