Extra-nodal monocytoid B-cell lymphoma of the urinary bladder.

Monocytoid B-cell lymphoma (MBCL) is a low-grade neoplasm considered to be the neoplastic counterpart to monocytoid B-lymphocytes, derived from marginal zone lymphocytes. Recently, a 72-yr-old woman presented with urinary symptoms of burning, urgency, and hematuria. Examination of the urinary bladder revealed the presence of an exophytic mass at the bladder base. This lesion was grossly suspected of being a transitional cell carcinoma, but on initial histologic examination it was found to be lymphoma composed of cells with moderately abundant cytoplasm and an overall size reminiscent of a large cell type. Detailed histologic examination led to a diagnosis of MBCL in this submucosal site. Clinical staging showed no evidence of lymphoma in other organs and the patient responded to therapy for non-Hodgkin lymphoma (NHL). This case represents an unusual presentation of low-grade NHL and may be consistent with previous suggestions of a relationship between MBCL and lymphomas of mucosa-associated lymphoid tissue.