CXCR4 and neoplasm: Interestingly, for many years, it was assumed that CXCR4 was the only SDF-1 receptor; however, recent studies have demonstrated that CXCR7 is a novel receptor of SDF-1 involved in several aspects of tumor invasion and metastasis in PDAC [81, 91, 92]; Liu et al. reported that SDF-1 and CXCR7's expression in the ductal cells were related with poor prognosis, as the median survival time of SDF-1+CXCR7+ patients was 6 months while that of SDF-1−CXCR7− patients was 10 months [81].