CXCL12 and neoplasm: All these data demonstrate that Brca1 deficiency (Fig. 8) creates a tumor-permissive environment in mammary tissues through activation of the S100A9-CXCL12 axis, which renders cancer cells insensitive to ICB, and the inhibition of S100A9-CXCL12 signaling could sensitize the cancers to ICB.