This patent application relates to the treatment of cancer and other diseases that have a CD47+ phenotype. Treatment involves the use of radiation and a CD47 -binding agent, preferably a CD47-binding form of human signal regulatory protein alpha (SIRPa) that inhibits activation of the CD47/ SIRPa axis and mediates phagocytosis of CD47+ disease cells. An anti-cancer effect of a CD47 blocking agent is enhanced when combined with radiation therapy. The anti-cancer effect of a CD47 blocking agent such as SIRPaFc is enhanced when combined with radiation therapy.
