SIRPA and brain neoplasm: However, considering the heterogeneity of GB, researchers have tried to find target binding antigens in the tumor microenvironment, including the overexpressed insulin-like growth factor binding protein 7 (IGFBP7) in the blood vessels of brain tumors (54), as well as signal regulatory protein alpha (SIRPα) significantly expressed by microglia- and monocyte-derived tumor-associated macrophages (TAMs) (113).