CD34 and neoplasm: OS cells (Saos–2 cell line) downregulate the expression of angiogenic factors, such as CD34, PDGFA, PDGFRA, PDGFRB, and VEGF, in human AD-MSCs when co-cultured, implying that MSCs cannot differentiate in vitro under the induction of tumor cells and do not support tumor angiogenesis in vivo [60].