Chaturvedi et al. further implicated hypoxia-induced factors (HIFs) as a trigger for MSC homing to primary tumors, facilitated in part by CCL5/CCR5 and an additional reciprocal MSC-tumor cell feedback loop promoting placental growth factor (PGF) expression by breast tumor cells to reinforce MSC recruitment, angiogenesis, and increased lung and lymph node metastasis (Chaturvedi et al., 2012). Here, PGF is linked to neoplasm.