CXCR4 and hemangioblastoma: In the 16 sporadic hemangioblastomas the mean percentage of CXCR4 positive cells per specimen (16 %, range 1–38 %) was higher as compared to the 13 VHL-related hemangioblastomas (8 %, range 3–19 %, P = 0.002; Fig. 2b; Table 2).