CD5 is aberrantly expressed in B cell chronic lymphocytic leukemia (B-CLL) and mantle cell lymphoma (MCL), while other B cell malignancies, including hairy cell leukemia (HCL) and B cell prolymphocytic leukemia (B-PLL), Diffuse Large B-cell Lymphoma (DLBCL), Follicular Lymphoma (FL), Splenic marginal zone lymphoma (SMZL), and even B-Acute Lymphoblastic Leukemia (B-ALL), are usually CD5 negative or weakly positive [73]. The gene discussed is CD5; the disease is hairy cell leukemia.