In sharp contrast to the remarkably heterogeneous profile of genomic aberrations in CLL, MCL is characterized by the almost ubiquitous presence of the t(11;14) (q13;q32) chromosomal translocation underlying the formation of the IGH/CCND1 fusion gene and, ultimately, leading to cyclin D1 overexpression, a true pathologic hallmark of MCL (142, 143). The gene discussed is CCND1; the disease is B-cell chronic lymphocytic leukemia.