ARG1 and cancer: It is well established that tumor secreting cytokines such as CCL2 and CCL5 attract macrophages polarized to support cancer cell dissemination (35, –37, 43, , , , , , –50), and consistently we find increased levels of Arginase 1 (as a marker of these myeloid cells in neoplastic pancreas) in TIGAR null primary tumors and metastases.