Cyclin D1 overexpression due to t(11;14)(q13;q32) involving the IGH locus on chromosome 14 and CCND1 (cyclin D1) locus on chromosome 11 is a constant finding in MCL. However, about 7% of mantle cell lymphomas are negative for cyclin D1 and instead produce cyclin D2 or cyclin D3. Rare cases of variant CCND1 translocation involving immunoglobulin light chains have been reported. It must also be kept in mind that Cyclin D1 overexpression by immunohistochemistry has been reported in multiple myeloma, hairy cell leukemia, proliferation centers of CLL, and splenic marginal zone lymphomas. Image courtesy of: Genevieve Crane, MD, PhD, Johns Hopkins Hospital, Baltimore, Maryland, USA.