Title PagePrimary Diffuse Large B-Cell Lymphoma of the Seminal Vesicles: A Rare Case with Diagnostic and Therapeutic ImplicationsMohammad Soleimani, Mostafa Farajpour, Behrang KazeminejadKeywords: DLBCL, Seminal Vesicle, Lymphoma, R-CHOP, Pelvic Mass, HydroureteronephrosisKey Clinical MessagePrimary diffuse large B-cell lymphoma of the seminal vesicles is rare but treatable. Multimodal imaging and biopsy confirmed the diagnosis in a 68-year-old male. Eight cycles of R-CHOP chemotherapy achieved a favorable outcome, emphasizing early intervention in atypical pelvic masses.IntroductionPrimary tumors of the seminal vesicles are uncommon, with most cases representing secondary involvement from adjacent organs (e.g., prostate, bladder) or distant metastases. Primary seminal vesicle lymphomas, particularly diffuse large B-cell lymphoma (DLBCL)—the most common subtype of non-Hodgkin lymphoma—are exceptionally rare and poorly documented. Unlike typical extranodal lymphoma sites (e.g., gastrointestinal tract, skin), the seminal vesicles present unique diagnostic difficulties due to their rarity and nonspecific symptoms, often mimicking urological conditions. This report describes a rare case of primary DLBCL of the seminal vesicles, aiming to enhance clinician awareness, outline diagnostic challenges, and discuss therapeutic strategies based on a 68-year-old male patient’s presentation and management.Case History/ExaminationA 68-year-old male presented with a 4-week history of intermittent, dull flank pain that progressively worsened. He had no prior hematuria, renal, or prostate issues; last year’s abdominopelvic sonography was normal. Physical examination revealed flank discomfort on palpation. Digital rectal examination (DRE) identified a palpable mass in the right seminal vesicle, raising suspicion of an abscess or malignancy. Laboratory results showed elevated creatinine at 2.5 mg/dL, suggesting renal impairment possibly due to ureteral obstruction. Imaging studies included:- Abdominopelvic Sonography: Right hydroureteronephrosis.- CT Scan (non-contrast): A 44 x 35 mm soft-tissue mass in the right seminal vesicle, compressing the ureter, with no calcification (Figure 1).- Bi-parametric MRI: A hyperintense T2-weighted, hypointense T1-weighted mass in the right seminal vesicle, consistent with malignancy (Figure 2).- PET-CT: Hypermetabolic mass involving the seminal vesicle, prostate, and bladder wall; hypermetabolic lymph nodes in bilateral iliac, para-aortic, and mediastinal regions; and two foci in the gastric body.- Chest CT: No evidence of metastasis.Histopathology and immunohistochemistry (IHC) from a biopsy revealed large, atypical tumor cells with vesicular nuclei and prominent nucleoli. IHC showed: CD20+ (diffuse), CD79a+, BCL2+ (80%), BCL6+ (40%), CD10-, MUM1+ (80%), and Ki67 ~70%, confirming DLBCL (Figures 3, 4). The patient underwent eight cycles of R-CHOP (Rituximab 375 mg/m², Cyclophosphamide 750 mg/m², Doxorubicin 50 mg/m², Vincristine 1.4 mg/m², Prednisone 100 mg/day for 5 days) over five months. Filgrastim was used to manage neutropenia. No significant dose adjustments were required. Written informed consent was obtained from the patient for publication of this case report.Differential DiagnosisInitial considerations included urinary tract malignancy, benign prostatic hyperplasia, secondary seminal vesicle tumors, or abscess, prompted by hydroureteronephrosis and DRE findings. DLBCL was confirmed post-biopsy, ruling out alternatives like sarcoma or benign vesicular tumors due to IHC and imaging characteristics.Conclusion and Results (Outcome and Follow-up)Follow-up PET-CT at 3 and 6 months showed a marked response: the pelvic mass reduced in size and metabolic activity, and hypermetabolic lymph nodes resolved. A persistent hypermetabolic focus in the right prostate lobe prompted a TRUS-guided biopsy, which was negative for malignancy. The gastric foci were not pursued further due to clinical improvement and lack of symptoms. This case highlights primary DLBCL of the seminal vesicles as a rare but critical differential in pelvic masses. Multimodal diagnostics and early R-CHOP initiation were pivotal to achieving a favorable outcome. Clinicians should remain vigilant for lymphoma in atypical urological presentations, supported by integrated imaging and histopathology.DiscussionPrimary DLBCL of the seminal vesicles is a diagnostic rarity, often mistaken for common urological conditions like abscesses or prostatic hyperplasia due to its nonspecific presentation (e.g., flank pain, pelvic mass). This case exemplifies the challenge, as initial findings suggested a urinary tract issue, yet comprehensive evaluation—DRE, sonography, CT, MRI, and histopathology—revealed DLBCL. Compared to prior reports [1-3], our case is notable for extensive lymphatic involvement and gastric foci, though their relevance remains unclear without further investigation. The diagnostic process underscores the value of multimodal imaging and IHC, with CD20 positivity and high Ki67 index confirming the aggressive B-cell lineage. Unlike Zhu et al. [2], who reported renal failure, our patient’s creatinine elevation was reversible with treatment, suggesting obstruction rather than parenchymal damage. Therapeutically, R-CHOP yielded a robust response, aligning with outcomes in seminal vesicle DLBCL cases [5, 6], though the persistent prostatic lesion highlights the need for vigilant follow-up. Limitations include the short follow-up period and lack of genetic subtyping (e.g., germinal center vs. activated B-cell DLBCL), which could refine prognosis. A multidisciplinary approach involving urology, oncology, and pathology was critical to success, emphasizing its necessity in rare extranodal lymphomas.Conflict of InterestThe authors declare no conflict of interest.Author ContributionsMohammad Soleimani contributed to the conceptualization and methodology of the study. Mostafa Farajpour was responsible for conceptualization, data curation, investigation, and writing the original draft. Behrang Kazeminejad contributed to data curation, investigation, and writing, reviewing, and editing the manuscript.ConsentWritten informed consent was obtained from the patient for the publication of this case report and any accompanying images.References1. Kwag KS, et al. Primary diffuse large B-cell lymphoma of the seminal vesicle: A case report. Investigative Magnetic Resonance Imaging. 2016;20(4):259-63.2. Zhu J, et al. Primary diffuse large B-cell lymphoma of the seminal vesicles: Ultrasonography and computed tomography findings. Urology. 2011;78(5):1073-4.3. Zhu B, et al. Primary lymphoma of the seminal vesicles presented with acute renal failure: PET-CT findings. Open J Urol. 2012;2:137.4. Handa N, et al. Seminal vesicle involvement: A rare extranodal manifestation of non-Hodgkin’s lymphoma. BMJ Case Rep. 2016;2016:bcr2016217045.5. Garcia Fernandez A, et al. Seminal vesicles tumor: Rare localization of lymphoma. Urol Case Rep. 2021;36:101560.6. Harley F, et al. Primary non-metastatic extra-nodal diffuse large B-cell lymphoma of the prostate and seminal vesicle. Urol Case Rep. 2022;40:101945.Figure LegendsFigure 1: Axial CT scan showing a 44 x 35 mm mass in the right seminal vesicle causing ureteral compression.Figure 2: Bi-parametric MRI of the right seminal vesicle mass. (A) Axial T1-weighted image showing a hyperintense mass with adjacent compression. (B) Coronal T2-weighted image demonstrating the mass with ureteral compression effects. (C) Sagittal T2-weighted image highlighting the extent of the mass and its impact on surrounding structures.Figure 3: Immunohistochemical staining for CD20 (x400) showing diffuse membranous positivity in tumor cells.Figure 4: Immunohistochemical staining for Ki67 (x400) indicating high proliferative activity (~70%).