[Primary lymphomas in urinary bladder: a clinicopathological analysis of 23 cases].

Objective: To investigate the clinicopathological features, diagnosis and differential diagnosis of primary bladder lymphoma. Methods: A retrospective study was conducted on 23 cases of primary bladder lymphoma diagnosed at Beijing Friendship Hospital of Capital Medical University between February 2010 and April 2024. The clinicopathological data were collected and analyzed, and literature was reviewed. Results: Among the 23 cases, 7 were male and 16 were female, with a male-to-female ratio of 1.0∶2.5. The median age was 65 (58, 71) years, ranged 38-84 years. The main clinical manifestation was painless visible hematuria, followed by frequent urination, urgency, and lower abdominal discomfort. Only one case presented with fever, and all cases primarily presented as bladder masses or lesions. The histological types included 17 cases of extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (EMZL), 4 cases of diffuse large B-cell lymphoma (DLBCL), 1 case of ALK-negative anaplastic large cell lymphoma (ALCL), and 1 case of indolent NK-cell lymphoproliferative disease (INKLPD). EMZL exhibited relatively uniform morphology. Among them, 2 cases showed marked plasmacytic differentiation, 1 case had an increased number of large cells, 6 cases had residual germinal centers, and 2 cases presented with lymphoepithelial lesions. All cases demonstrated irregular FDC networks. DLBCL cells were larger in size; 3 cases showed diffuse infiltration, while 1 case had scattered, clustered distribution in a background of small lymphocytes,and with aberrant expression of GATA3. ALCL negative ALCL showed classic anaplastic morphology with "kidney-shaped" nuclei. INKLPD cells were of medium size and irregular in shape, with some cells containing eosinophilic granules in the cytoplasm. EBER in situ hybridization was negative. Conclusions: The primary histological types of bladder lymphoma are EMZL and DLBCL, with occasional cases of T-cell lymphoma and INKLPD. Clinical manifestations lack specificity and may overlap with inflammatory conditions or epithelial tumors. Both clinicians and pathologists should be aware of these rare diseases to facilitate accurate diagnosis and treatment.