CXCR4 and cancer: A subgroup of three resistant tumors (BoC20, 60, and 69) showed markedly higher expressed genes involved in cancer stem cell signaling, such as OLFM4, CXCR4, ALDH1A1, or ALDH1A3. This was accompanied by a striking upregulation of defensins (DEFA5 and DEFA6) together with an activation of the Notch pathway via the ligand DLL1 in two of the three tumors (Additional file 2: Fig. S10, Additional file 7: Table S6).