The interference of chemotherapeutics with the CXCL12-CXCR4 axis might explain why patients in our study with overexpression of CXCR4 in recurrent cancer biopsies have a smaller number of chemotherapy cycles because CXCR4 is one of the key molecules in the mechanism of action of cisplatin-based chemotherapy. The gene discussed is CXCL12; the disease is cancer.