CD34 and cancer: Finally, cancer-associated fibroblasts (CAFs), identified by their high expression of CAF markers, interacted with EPCs and CD34+ Pro-B cells via CXCL12/CXCR4, promoting tumor progression and angiogenesis (Figures 1D, Supplementary Figures S10I, S5D, N), as found in many tumor studies where CAFs promote tumor invasion via CXCL12/CXCR (23–29).