CXCR4 and neuroblastoma: Surprisingly, overexpression of CXCR4 did not lead to induction of metastases in the non-metastatic NB cell line IGR-NB8 and did not increase the frequency of metastases formed by the metastatic IGR-N91 cell line, which constitutively expresses moderate levels of CXCR4 [19] (Figure 2d, Fisher's exact test: p = 0.38).