CXCR4 and cancer: Accordingly, several studies have exhibited that combination therapy with ICIs plus other therapeutic approaches, such as chemotherapy [24–26], radiotherapy [27, 28], cancer vaccines [29–31], anti-angiogenic agents [32–34], HER-2 targeted therapies [35] and also CXCR4 blockade therapy [36, 37] can efficiently circumvent tumor resistance to ICI therapy.