Urinary bladder wall mass with neoplastic lymphoid cells in the urine: Diagnosis of an IgG secretory B-cell lymphoma with Bence-Jones proteinuria in a dog.

In this study, we describe a multimodal approach to diagnose a unique case of myeloma-related disease, extranodal secretory B-cell lymphoma with urinary bladder involvement, an IgG4 monoclonal gammopathy, and Bence-Jones proteinuria in a dog with a 6-year history of hyperglobulinemia that had not been further evaluated. A 12-year-old dog was presented for evaluation of a 1-week history of tenesmus. Urine sediment cytologic evaluation revealed low to moderate numbers of intermediate to large-sized lymphocytes. We describe a technique that yielded adequate numbers of viable neoplastic cells in shipped urine sediment for PARR and flow cytometry. Those studies demonstrated a clonal immunoglobulin gene rearrangement and an expansion of CD21-positive and MHC Class II-negative B cells, respectively. Protein electrophoresis with immunofixation and proteomic evaluation revealed a serum and urine IgG4 monoclonal gammopathy with Bence-Jones proteinuria. MUM1 immunocytochemistry performed on the urine sediment slides failed to label the neoplastic cells; thus, a plasma cell tumor was considered unlikely. Lack of response to a cyclophosphamide, vincristine, and prednisone chemotherapy regimen led to euthanasia without necropsy 21 days after diagnosis. Lymphoma is the most common hematopoietic malignancy and accounts for up to a quarter of all neoplasms in dogs, but lymphoid neoplasms arising primarily from extranodal sites are infrequently reported. Urinary tract neoplasia can be diagnosed by urine evaluation in about one-third of canine cases, but the diagnosis of lymphoid neoplasia via urine evaluation is rarely reported. This case highlights the utility of ancillary diagnostics on urine for detection of lymphoid malignancies.