CCL2 and neoplasm: Fibrocytes are identified by expression of myeloid progenitor cell markers coupled with markers for myofibroblasts, including SMA and collagen I. To examine changes in the myeloid progenitor cell population during tumor development, we humanized NOD/SCID mice with either SVF/EV or SVF/CCL2 cells, then transplanted human breast epithelial cells transduced with SV40ER and KRasG12V into the humanized mammary glands.