RT Journal Article SR Electronic T1 Cyclin D1 overexpression in proliferation centres of small lymphocytic lymphoma/chronic lymphocytic leukaemia JF Journal of Clinical Pathology JO J Clin Pathol FD BMJ Publishing Group Ltd and Association of Clinical Pathologists SP 899 OP 902 DO 10.1136/jclinpath-2017-204364 VO 70 IS 10 A1 Larissa Sena Teixeira Mendes A1 Natalie Peters A1 Ayoma D Attygalle A1 Andrew Wotherspoon YR 2017 UL http://jcp.bmj.com/content/70/10/899.abstract AB The recent publication reviewing the updated WHO classification commented on the presence of cyclin D1-positive cells in the proliferation centres (PC) of small lymphocytic lymphoma/chronic lymphocytic leukaemia (SLL/CLL). The figure quoted was 30%, which appeared higher than our experience. To assess cyclin D1 expression in PC of SLL/CLL cases, we performed a review of SLL/CLL cases diagnosed at the Royal Marsden Hospital between 1996 and 2009. Of 105 SLL/CLL cases, 16.2% showed expression of cyclin D1 in PC with none carrying the translocation t(11;14)(q13;q32). Our study and a review of the published literature suggest that this phenomenon occurs with a significantly lower prevalence than that described in the recent review of the updated WHO classification. We confirm that cyclin D1 expression is confined to PC with the typical small lymphocytes being negative. This finding is apparently unrelated to the translocation involving CCND1 and IGH genes.