Identification of CD5/SOX11 double-negative pleomorphic mantle cell lymphoma

Cyclin D1 protein-positive diffuse large B cell lymphoma (DLBCL) has an immunophenotype of CD5(-) cyclin D1(+) SOX11(-), and most cases lack a CCND1 rearrangement and have a gene expression profile of DLBCL. Rarely, cyclin D1 protein-positive DLBCL harbors a CCND1 rearrangement, and some genetic copy number features typical of mantle cell lymphoma (MCL) have been detected. Since gene expression studies have not been performed, whether such CCND1-rearranged cases represent cyclin D1 protein-positive DLBCL or CD5/SOX11 double-negative pleomorphic MCL remains unclear. To date, no cases of CD5/SOX11 double-negative MCL have been reported. In this study, we collected eight cases initially diagnosed as cyclin D1 protein-positive DLBCL, including four with a CCND1 rearrangement and four without. Immunohistochemically, all four CCND1-rearranged cases had >50% of tumor cells positive for cyclin D1 protein, whereas only one (25%) non-rearranged case had >50% positive tumor cells. Analysis of genome-wide copy number, mutational, and gene expression profiles revealed that CCND1-rearranged cases were similar to MCL, whereas CCND1-non-rearranged cases resembled DLBCL. Despite the SOX11 negativity by immunohistochemistry, CCND1-rearranged cases had a notable trend (P = 0.064) of higher SOX11 mRNA levels compared to non-rearranged cases. Here, we show for the first time that CCND1 rearrangement could be useful for identifying CD5/SOX11 double-negative pleomorphic MCL in cases diagnosed as cyclin D1 protein-positive DLBCL. Cases with >50% cyclin D1 protein-positive tumor cells immunohistochemically and higher SOX11 mRNA levels are more likely to have a CCND1 rearrangement, and fluorescence in situ hybridization can be used to detect the rearrangement.