MCL is characterized by monomorphic small to medium-sized lymphoid cells with CD5⁺, CD10⁻, CD23⁻ phenotype.² CCND1 rearrangement and/or CCND1 immunostaining is a hallmark of diagnosis. However, it has been known that CCND1-negative MCL with a poor clinical outcome exists. Recently, SOX11 has been shown to be a good marker to identify such cases with poor outcome,⁵ although a controversy has been raised.⁷  Salaverria et al revealed that CCND2 gene rearrangement is frequently found (22 of 40 CCND1-negative MCL cases, 55%) and is a molecular basis for CCND1-negative SOX11-positive MCL (yellow box).¹  Further study on molecular mechanisms of CCND1-negative CCND2-negative SOX 11-positive MCL with a poor clinical outcome (orange box) to provide appropriate therapy is needed. *More than half (22/40) of the CCND1-negative SOX11-positive MCL show CCND2 gene rearrangement. **Translocation of CCND2 takes place predominantly with IG light chain genes (15/22). ***Among CCND1-negative SOX11-positive MCL cases, 18 of 40 did not show CCND2 translocation. Because controversy exists on SOX11 staining with regard to clinical outcome, further study including identification of other diagnostic markers and molecular basis is warranted. ****CCND1-negative indolent MCL has not been well recognized and would be rare, but its understanding is important for selecting appropriate therapy and for differential diagnosis from the other types of lymphoma.