The present invention relates to the identification of a novel role of CXCR-4 in cell transformation and aberrant cellular proliferation. In particular, the present invention relates to the altered gene expression of CXCR-4 in a number of primary tumors and cell lines derived from tumors, in addition to, the altered gene expression of ligands for CXCR-4. Further, the present invention relates, in part, to the Applicants' surprising discovery that the inhibition of CXC R- 4 gene expression or the inhibition of CXCR-4 activity in transformed cells reverses the transformed phenotype.