CXCR2 and metastatic squamous cell carcinoma: Currently the following MDSC inhibitors are in clinical trials [221]: Reparixin (CXCR2) is in Phase 2 clinical trials for TNBC (NCT02370238); AZD5069 (CXCR2) is in Phase 1b/2 for advanced solid tumours and metastatic squamous cell carcinoma (NCT02499328); Plexidartinib (CSF-1R) is in Phase 2 for recurrent glioblastoma (NCT01349036); and Maraviroc (CCR5) is in Phase 1 for metastatic colorectal cancer (NCT01736813).