Flow cytometry in the diagnosis and monitoring of lymphoma based on urine samples: a case report.

INTRODUCTION

Diffuse large B-cell lymphoma rarely presents primarily with urinary symptoms, making noninvasive diagnosis challenging. We report a case in which urine flow cytometry substantially aided diagnosis and monitoring.

METHODS

A 67-year-old man presenting with gross hematuria and painful urination underwent cystoscopy with biopsy and urine flow cytometry. B-cell immunophenotyping was performed using a targeted CD marker panel, and residual disease was tracked longitudinally after chemotherapy.

RESULTS

Histopathology suggested aggressive B-cell lymphoma. Urine flow cytometry identified an abnormal mature B-cell population (20.36% of nucleated cells) expressing CD45, CD19, CD20, CD10, FMC7, and λ, confirming a CD5-negative/CD10-positive phenotype. Following treatment with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone, the percentage of abnormal urinary B cells declined to 0.41% at 2 weeks, 0.18% at 1 month, and 0% at 3 months, coinciding with partial clinical remission.

DISCUSSION: Urine flow cytometry is a highly accessible, noninvasive, and effective tool. It provides critical diagnostic value and quantitative monitoring utility for hematologic malignancies involving the urinary tract and should complement-not replace-histopathology and urine cytology.