Painful penile mass as an initial manifestation of systemic diffuse large B-cell lymphoma: a case report.

BACKGROUND: Diffuse large B-cell lymphoma (DLBCL) involving the penis is an exceptionally rare extranodal malignancy and is frequently misdiagnosed as penile carcinoma or infectious conditions because of its nonspecific clinical presentation. CASE PRESENTATION: A 58-year-old man presented with a progressively enlarging painful penile mass for 3 months that was refractory to empirical antibiotic therapy. Ultrasound-guided core biopsy of the penile shaft mass revealed diffuse large B-cell lymphoma, centroblastic type, non-germinal center B-cell subtype with MYC and BCL-2 double expression. Fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) demonstrated intense uptake in the penis with additional gastric involvement confirmed by biopsy, consistent with Lugano stage IV disease. The patient received curative-intent systemic chemo-immunotherapy with Rituximab plus Cyclophosphamide, Doxorubicin, Vincristine, and Prednisone (R-CHOP) and subsequently achieved complete metabolic remission on follow-up FDG PET/CT. CONCLUSION: This case highlights an unusual presentation of systemic DLBCL as a painful penile mass and underscores the pivotal role of FDG PET/CT in detecting occult extranodal involvement, accurately staging disease, and guiding appropriate management.