HGBL-NOS presenting as widespread extranodal disease without lymphadenopathy: a case report.

High-grade B-cell lymphoma, not otherwise specified (HGBL-NOS), is a rare and highly aggressive B-cell lymphoma with overlapping morphologic and immunophenotypic features that complicate distinction from other aggressive B-cell lymphomas. Disseminated extranodal involvement, absence of lymphadenopathy, and lack of standardized treatment guidelines pose significant diagnostic and therapeutic challenges in HGBL-NOS. We report a 27-year-old female who presented with a six-month history of progressive left-sided chest pain, dyspnea, hemoptysis, and dry cough without constitutional B symptoms. Laboratory evaluation revealed anemia and markedly elevated lactate dehydrogenase (LDH) levels. Imaging revealed a large, heterogeneous mass in the anterior left lung with disseminated extranodal involvement of 11 organs, including the lungs, heart, brain, kidneys, adrenal glands, uterus, spleen, pancreas, bone, skeletal muscle, and thyroid, in the absence of lymphadenopathy. Endobronchial ultrasound-guided transbronchial (EBUS) biopsy confirmed infiltration by atypical large B-cell lymphoid cells. Immunohistochemistry revealed diffuse positivity for CD20, CD10, and BCL6, with C-MYC expression in 40% of tumor cells and a Ki-67 proliferation index of 90%. The patient received R-CEOP for cytoreduction, followed by four cycles of intensive R-CODOX-M/IVAC chemotherapy, with dose adjustment based on hepatic and cardiac tolerance. Post-treatment positron emission tomography/computed tomography (PET/CT) confirmed complete metabolic remission. This case highlights an exceptionally rare and aggressive presentation of HGBL-NOS with extensive extranodal dissemination involving 11 organs in the absence of lymphadenopathy, underscoring the importance of early integrated diagnostic approaches and prompt initiation of intensive chemotherapy to achieve favorable outcomes.