Exploring the Genetic Landscape of Primary Marginal Zone Lymphoma of the Urinary Bladder

Extranodal marginal zone B-cell lymphoma (MZL) of mucosa-associated lymphoid tissue is the most frequent primary lymphoma of the urinary bladder. Although MZLs from various anatomical sites are often associated with autoimmune disorders, infections, and site-characteristic genetic alterations, the molecular foundations and potential infectious triggers of urinary bladder MZL remain poorly understood. To elucidate the disease etiology and correlation with MZLs arising in other locations, we examined a cohort of 17 cases (11 women and 6 men) diagnosed with primary bladder MZL between 2005 and 2025. Immunohistochemical analysis confirmed the literature, with all samples testing positive for the pan B-cell markers CD20 and CD79a and negative for CD5 (except 1), cyclin D1, and SOX11. Thirteen samples exhibited secretory differentiation and displayed immunoglobulin light chain restriction (9 κ and 4 λ). No gene rearrangements in BCL2, BCL6, BCL10, IRF4, MALT1, and MYC were detected. High-throughput sequencing identified 31 pathogenic/likely pathogenic somatic mutations across 18 genes, with TBL1XR1 (n = 8), MAP2K1 (n = 4), and TNFAIP3 (n = 2) being the most frequently mutated ones. Additionally, all cases included variants of unknown significance. The sample of 1 patient tested positive for Chlamydia trachomatis, human betaherpesvirus 6B, and Epstein-Barr virus. Escherichia coli was detected in 5 samples. We provide compelling evidence that urinary bladder MZL is a point mutation-driven disease rather than gene fusion-driven disease and that E coli is present in approximately one-third of tumor biopsies. These tumors frequently harbor pathogenic mutations in genes encoding components regulating plasma cell differentiation and the pleiotropic MAPK/ERK signaling pathway. TBL1XR1, which was unexpectedly frequently mutated, is generally linked to more aggressive variants of MZL and diffuse large B-cell lymphoma; however, its prognostic significance in urinary bladder MZL remains to be determined. Comparative analysis highlighted partial overlap of urinary bladder MZL mutational profiles with those found in salivary gland MZL.