Primary Diffuse Large B-Cell Lymphoma of the Urinary Bladder: Update on a Rare Disease and Potential Diagnostic Pitfalls.

Diffuse large B-cell lymphoma (DLBCL) represents the most frequent type of non-Hodgkin lymphoma. Globally, DLBCL is an aggressive disease, requiring an accurate diagnosis and prompt treatment. The diagnosis is often made on biopsy samples of a nodal mass, however, approximately 40% of DLBCL cases arise at extranodal sites. The most common extranodal site is the gastrointestinal tract, however any extranodal area may be primarily involved. Primary urinary bladder lymphoma represents only 0.2% of extranodal non-Hodgkin lymphomas, whereas secondary involvement of the urinary bladder by a systemic lymphoma is a more common event. Despite being rare, DLBCL is considered to represent the predominant primary urinary bladder lymphoma. The majority of cases reported in the bladder belong to the DLBCL, NOS group, and there are only rare cases of EBV-positive DLBCL, NOS. In this review, we summarize the current knowledge on DLBCL primarily occurring in the urinary bladder, with the aim of increasing clinician and pathologist awareness on this aggressive lymphoma rarely arising in the urinary bladder. Additionally, we focus on those entities which should be taken into consideration in the differential diagnosis, highlighting potential diagnostic pitfalls.