Indeed, SCLC cell lines and primary tumour cells express high levels of CXCR4 (Kijima et al, 2002; Burger et al, 2003), and CXCR4 ligand CXCL12 is constitutively expressed by bone marrow stromal cells (Muller et al, 2001). This evidence concerns the gene CXCL12 and small cell lung carcinoma.