CXCR4 and neoplasm: Functionalization of ReANCs with the small molecule AMD3100, an antagonist of tumor-expressed C-X-C chemokine receptor type 4 (CXCR4), showed higher retention in CXCR4-positive tumors, allowing for detection of sub-tissue microlesions as small as 18.9 mm3 and about 1 cm deep (Zevon et al., 2015).