title: Primary mediastinal large B-cell lymphoma and its mimickers: a rare case report with literature review.
abstract: Primary mediastinal large B-cell lymphoma (PMLBL) is an uncommon non-Hodgkin lymphoma with a distinct clinicopathological entity in the WHO classification of lymphoid malignancies. It is known to originate from B-cells of the thymus. It mimics thymic neoplasms and other lymphomas clinically and histopathologically. We reported a 33-year-old obese man who presented with shortness of breath off and on for 4 years. Radiologically, there was a huge anterior mediastinal mass. Tru-cut biopsy was initially diagnosed as type-A thymoma. Histopathological examination of the excised specimen revealed PMLBL with stromal fibrosis and sclerosis which created a diagnostic difficulty. The neoplastic cells varied from medium-sized to large pleomorphic cells, including mononuclear cells with centroblastic and immunoblastic features as well as bi-lobed Reed Sternberg (RS)-like cells and horse-shoe like hallmark cells. Some interlacing spindle cells and epithelioid cells were also present. Immunohistochemically, tumour cells expressed diffuse positivity for LCA, CD20, CD79a, CD23, Bcl2, MUM-1 and heterogenous positivity for CD30 and EMA, and were negative for CD10, CD15 and ALK. Ki67 scoring was very high. Tumour cells infiltrated into peri-thymic fat and pericardium. No malignant cells were detected in the pleural fluid and there was no bone marrow infiltration. The patient showed partial response to 6 cycles of RICE chemotherapy, and was planned for second line chemotherapy using hyper-CVAD regimen followed by autologous stem cell transplantation. This case illustrates the importance of thorough sampling and immunohistochemistry in differentiating PMLBL from its differential diagnoses.
authors: University Sains Malaysia, School of Medical Sciences, Pathology Department, 16150 Kubang Kerian, Kelantan, Malaysia. safiya@usm.my.
authors: T T
authors: TT
authors: Win
authors: Z
authors: Z
authors: Kamaludin
authors: A
authors: A
authors: Husin
mesh_terms: D000328:Adult; D014408:Biomarkers, Tumor / Q000032:analysis; D003937:Diagnosis, Differential; D006801:Humans; D007150:Immunohistochemistry; D016403:Lymphoma, Large B-Cell, Diffuse / Q000175:diagnosis* / Q000473:pathology; D008297:Male; D008479:Mediastinal Neoplasms / Q000175:diagnosis* / Q000473:pathology; D013945:Thymoma / Q000175:diagnosis; D013953:Thymus Neoplasms / Q000175:diagnosis
chemical_list: D014408:Biomarkers, Tumor