CXCR4 and neoplasm: Most interestingly, expression of CXCR4, CXCR2, and L-selectin/CD62L (figure 1D, online supplemental figure S2) did not significantly differ between chronologically aged (BrdUneg) and non-aged (BrdUpos) circulating as well as tumor-associated neutrophils in tumor-bearing mice, suggesting that in early stages of cancer chronological and biological aging of neutrophils in the systemic circulation is uncoupled.