CSF2 and neoplasm: In order to determine how closely these BM-MDSCs resembled their counterparts in tumor-bearing mice, we analyzed G-MDSCs from the spleen, lungs and tumors of PyMT-MMTV mice that develop tumors spontaneously in the mammary fat pad, for the expression of various cell surface receptors, and compared this with BM-MDSCs generated with GM-CSF and IL-6 in vitro (Fig 1C).