SIRPA and neoplasm: The demonstration that mCD47 enables PC-3 tumor cells to initiate spontaneous local and distant metastasis in CB17.Scid mouse that otherwise is resistant to the metastasis of the tumor cell reinforces the notion that CD47-SIRPα mediated action of macrophage probably plays a more important role than other innate immune components in determining the metastatic potential of xenograft tumors.