Schematic diagram illustrating evolution of the entity MCL. MCL was recognized in Kiel classification and modified Rappaport classification as centrocytic lymphoma and lymphocytic lymphoma of intermediate differentiation (IDL), respectively.⁶  Precise criteria for the distinction from other morphologically similar lymphomas were lacking. The recognition of a characteristic immunophenotype (CD5⁺, CD23⁻, CD10⁻, monoclonal B cell) helped better define the entity. The identification of the t(11;14) resulting in CCNDI/IGH translocation in virtually all cases of MCL led to the use of cyclin D1 detection by immunohistochemistry for diagnosis. In addition, secondary genetic events such as p53 and p16 deletion/mutation were identified in high-grade variants of MCL, which had been recognized histologically as the “blastoid” subtype. The data derived from immunophenotypic and genetic studies are integrated, culminating in our current definition of the disease. PDL indicates poorly differentiated lymphocytic; WDL, well-differentiated lymphocytic; DHL, diffuse histiocytic lymphoma; and MZL, marginal zone lymphoma.