Aberrant expression of CD10 and BCL6 in mantle cell lymphoma

Aims Mantle cell lymphoma ( MCL ) is characterized by distinctive histological and molecular features. Aberrant expression of BCL 6 and CD 10 has been reported occasionally, but the biological features of such cases are largely unknown. This study aimed to define the epidemiological, histological and cytogenetic characteristics of BCL 6 and CD 10‐positive MCL s, also investigating possible biological features. Methods and results A total of 165 cases of cyclin D1 and t(11;14)(q13;q34)‐positive MCL s were studied for CD 10 and BCL 6 immunohistochemical expression, which was documented in 26 of 165 (15.8%) cases ( BCL 6 17 of 165; CD 10 11 of 165; BCL 6 and CD 10 co‐expression two of 165). CD 10‐positivity was significantly more frequent in females (63.3%; P < 0.01). Either expression correlated significantly with higher mean proliferation index and higher prevalence of MUM 1 positivity ( P < 0.05). Fluorescence in‐situ hybridization ( FISH ) for BCL 6 (3q27) gene derangements was performed on the BCL 6‐ and CD 10‐positive cases and 98 matched controls: amplifications were documented more frequently in BCL 6‐positive than ‐negative cases (50.0% versus 19.4% of cases) ( P < 0.05). The mutational status of the variable immunoglobulin heavy chain genes ( IGVH ) was investigated by Sanger sequencing: five of the six successfully tested cases (83.3%) showed no somatic hypermutations. Conclusions Aberrant CD 10 and BCL 6 expression defines a subset of MCL s with higher mean Ki‐67 index and higher prevalence of MUM 1 expression. BCL 6 protein positivity correlates with cytogenetic aberrations involving the BCL 6 gene. Although examined successfully in few cases, the high prevalence of unmutated IGVH genes also points at a pregerminal cell origin for these phenotypically aberrant cases.