A 66-year-old man presented with a white blood cell count of 62.6 × 10⁹/L. Peripheral blood (PB) smear showed 80% small- to medium-sized atypical lymphoid cells with irregular to cleaved (panel A; original magnification ×500, Wright-Giemsa stain) or binucleated nuclear contours, and slightly condensed chromatin (panel B; original magnification ×1000, Wright-Giemsa stain). Bone marrow (BM) aspirate (panel C; original magnification ×500, Wright-Giemsa stain) and biopsy (panel D; original magnification ×400, hematoxylin and eosin stain) showed ∼70% atypical lymphoid cells with similar features to those of PB. These lymphoid cells were positive for CD20 (panel E; original magnification ×200) and CD5 (panel F; original magnification ×100), negative for CD3 (panel G; original magnification ×100) and cyclin D1 (not shown), but showed strong nuclear immunoreactivity for SOX11 (panel H; original magnification ×400) and ∼70% proliferation index by Ki-67 (panel I; original magnification ×200). Flow cytometry of PB and BM showed λ-restricted monotypic B cells, positive for FMC-7 but negative for CD23. Conventional karyotyping showed 46,XY[20], and fluorescence in situ hybridization analysis of BM showed no cyclin D1 or MYC rearrangements. A diagnosis of cyclin D1–negative blastoid mantle cell lymphoma (BMCL) was established.

This is an unusual BMCL with the following 3 features: initial leukemic presentation; markedly irregular to binucleated nuclear contours, which can be confused with other lymphomas such as follicular lymphoma or adult T-cell leukemia/lymphoma; and lack of cyclin D1 at both the protein and genetic level. Next-generation sequencing revealed KMT2D and TP53 mutations but no rearrangement of cyclin D2 or D3, respectively. Cyclin D1–negative MCL is difficult to recognize, but strong SOX11 nuclear immunoreactivity is helpful in this regard.