SIRPA and cancer: Since elevated CD47 mRNA expression correlates with poor prognosis of human cancers (Majeti et al. 2009; Willingham et al. 2012), CD47–SIRPα signaling plays an important role in cancer immune evasion and is a target for cancer immunotherapy (Chao et al. 2012; Alvey and Discher 2017; Veillette and Chen 2018).