Mantle cell lymphoma pathology update in the 2016 WHO classification

Mantle cell lymphoma (MCL) is an aggressive mature B-cell neoplasm genetically characterized by the presence of the t(11;14)(q13;q32) that leads to the constitutive overexpression of cyclin D1. The pathological and biological spectrum of this neoplasm has been expanded in recent years. This improvement in the knowledge of the disease has provided a better understanding of the diverse clinical evolution of the patients. The characterization of cyclin D1-negative MCL has led to the identification of cyclin D2 and D3 translocations as alternative mechanisms in this variant. Two major biological and clinical subtypes of the disease have been recognized, conventional and leukemic non-nodal MCL (nnMCL). MCL derives from CD5+ mature B-cells that have bypassed or experienced the germinal center microenvironment, retain a naive or memory-like epigenetic signature and carry a variable load of somatic mutations in the IGHV region; from truly unmutated to highly mutated, respectively. These two subtypes of tumors also differ in their genomic alterations, and clinical behavior, the conventional MCL (cMCL) being more aggressive than the leukemic nnMCL. This review will focus on the new aspects of the pathology of MCL in the updated 2016 WHO classification and its relevance for the clinical practice.