Mantle cell lymphoma (MCL) is an incurable B‐cell lymphoma characterized by a translocation that juxtaposes the CCND1 gene (which encodes cyclin D1, CD1) on chromosome 11q13 and an immunoglobulin heavy chain gene promoter on chromosome 14q32. The gene discussed is CCND1; the disease is B-cell non-Hodgkin lymphoma.