As a likely consequence of its high physiological expression on normal hematopoietic cells, CXCR4 surface levels are also particularly high in several hematologic malignancies, including non-Hodgkin lymphoma (NHL), multiple myeloma (MM), chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML), with substantial heterogeneity between diseases and within single entities. This evidence concerns the gene CXCR4 and B-cell chronic lymphocytic leukemia.