Abstract: Classical theories of origin for cancer assume that cancer can originate from the local body.Increased evidence shows that cancer can originate from the whole body but not local.We postulate that tumors originate from the origin cells of which tumor stagnate and replicate in suitable microenvironment.Moreover,tumor cells promote the form of tumor microenvironment,and tumor metastasis is only the growth of cancer initiating cells in suitable microenvironment.