A major component of tumor associated immune suppression is mediated by myeloid cells, especially the monocytic subset of myeloid derived suppressor cells (MDSC). In recent studies that were conducted through a CCSRI Innovation grant, the investigators discovered that oral treatment of mice with the commonly used histamine receptor 2 (H2) antagonists ranitidine or famotidine inhibits both primary breast tumor development and metastasis, in three distinct mouse tumor models and reduces the numbers of monocytic MDSC. These findings have enormous potential to aid in effective cancer immunotherapy and may have immediate implications for cancer patients.