CXCR4 and neoplasm: A very recent study by Rizzo et al., demonstrated that the presence of circulating tumor cells (CTCs) was significantly associated with BMs in a large cohort of 254 patients with GEP-NENs and that the proportion of CXCR4-positive CTCs was slightly higher in patients with BMs compared with those without (56% vs. 35%, p = 0.18) [42].