**6.8 Diffuse large B-cell lymphoma**

Diffuse large B-cell lymphoma (DLBCL) is the most common form of NHL. There is a slight male predominance. The median patient age is about 60 years, but can also occur in young adults and children.

DLBCL is molecularly heterogeneous. One frequent pathogenic event is dysregulation of BCL6. About 30% of DLBCLs contain various translocations that have in common a breakpoint in BCL6 at chromosome 3q27. Mutations are also seen in multiple other oncogenes including MYC and overexpression of the antiapoptotic protein BCL2. Tumors with BCL2 rearrangements usually lack BCL6 rearrangements. Co-expression of MYC with BCL2 and or BCL6 is now considered as double hit or triple hit lymphomas [1, 25, 63]. DLBCL typically presents as a rapidly enlarging mass at a nodal or extranodal site. Extranodal sites include the gastrointestinal tract, skin, bone, brain, and other tissues. Bone marrow involvement is relatively uncommon and usually occurs late in the course. Rarely, a leukemic picture emerges.
