In vitro and in vivo experiments on Lewis lung cancer, melanoma, pancreatic cancer, and neuroblastoma showed the downstream of a4B1 integrin and MCSF receptors and that RAC2 was activated to inhibit tumor development, metastasis, and macrophage differentiation into the M2 phenotype, thereby promoting tumor growth, angiogenesis, and invasion. Here, RAC2 is linked to neoplasm.