CXCL9 and cancer: This review also describes the structural complexity of the CXCR3 receptor, which allows its gene to be translated into three distinct isoforms (CXCR3-A, CXCR3-B, and CXCR3-alt) expressed heterogeneously in cancer [23], and its four main ELR-negative chemokines (CXCL9, CXCL10, CXCL11, and CXCL4), which bind differentially to CXCR3 receptors, eliciting different downstream signalling mechanisms [8].