A small number of malignant lymphoma cells detected in urine cytology and the characteristic cytological findings: A case of urinary tract involvement of diffuse large B-cell lymphoma

Cases in which malignant lymphoma (ML) is detected in urine cytology are rare; to the best of our knowledge, only eight cases of non-Hodgkin lymphoma that were detected on urine cytology have been reported. Herein, we report a case of diffuse large B-cell lymphoma (DLBCL) that was detected on urine cytology, focusing on the cytological findings. A 75-year-old man was referred to our hospital because of fever. Computed tomography showed a dense soft tissue lesion in the right lower ureter. Right hydronephrosis, a thickened bladder wall, and enlargement of the para-aortic, right external iliac, and inguinal lymph nodes were also observed. Clinically, upper tract or bladder urothelial carcinoma was suspected and urine cytology was performed. A small number of isolated atypical cells were detected, which showed high nuclear–cytoplasmic ratios, nuclear membrane irregularities, fine chromatin, and enlarged prominent nucleoli with scant clear cytoplasm. Liquid-based cytology with immunocytochemistry revealed that the atypical cells were positive for LCA and negative for CK AE1/AE3, suggesting the possibility of ML. In addition to urine cytology, atypical cells were observed in the urine sediment test. Bladder and inguinal lymph node biopsies were performed and a histological diagnosis of DLBCL (NOS, activated B-cell subtype) was made. Familiarity with and recognition of the characteristic cytopathological findings of ML on urine cytology are important for making a correct diagnosis.