CCL21 and neoplasm: Likewise, CCR7 chemokine ligands CCL19 and CCL21 enhance monocytes recruitment by forming heterodimers with CCL7 and CCL222, while heterodimers formed by CXCL9 and CXCL12 chemokines co-expressed in the perivascular area of the tumor enhance CXCR4-mediated recruitment of tumor-infiltrating lymphocytes and malignant B cells6.