CD47 and cancer: CD47, which functions as a ‘don’t eat me’ signal, can be highly expressed by cancer cells to subvert phagocytosis by signal-regulatory protein α (SIRPα)-expressing anti-tumour macrophages.121 CD47 is upregulated on circulating colorectal cancer cells,122 and its inhibition with neutralising antibodies reduces metastasis in a variety of mouse models and patient-derived xenografts.123–128