The four markers CD11c, CD25, CD103 and CD123 define the HCL score [8], which distinguishes HCL from other B cell haematological disorders associated with hairy cells, including the variant form of HCL (HCL-v), splenic marginal zone lymphoma (SMZL) and splenic red pulp lymphoma (SRPL). This evidence concerns the gene ITGAX and hairy cell leukemia.