When lymphoma masquerades as carcinoma: A rare case of primary nasopharyngeal diffuse large B-cell lymphoma with aberrant p63 expression

Primary nasopharyngeal diffuse large B-cell lymphoma (DLBCL) is an uncommon extra nodal lymphoma that may closely mimic nasopharyngeal carcinoma on clinical presentation, imaging, and histomorphology. Aberrant expression of epithelial markers, particularly p63, poses significant diagnostic challenges. 43-year-old man presented with recurrent cold-like symptoms, progressive nasal obstruction, aural fullness, and dysphagia for 8 to 9 months. Clinical examination revealed a nasopharyngeal mass without peripheral lymphadenopathy, and PET-CT showed a metabolically active posterior nasopharyngeal mass measuring approximately 4.5 x 3.8 x 4.9 cm, initially favouring carcinoma. Histopathology of biopsy from the mass demonstrated sheets, clusters, and cords of large atypical cells with high nuclear-to-cytoplasmic ratio, vesicular chromatin, prominent nucleoli, frequent mitoses, and focal necrosis, creating a strong impression of poorly differentiated carcinoma. Immunohistochemistry established the correct diagnosis: the tumour cells were positive for CD45, CD20, BCL2, BCL6, MUM1, with high Ki- 67 and aberrantly p63, while negative for CD10, pan-cytokeratin, CK5/6, S100, synaptophysin, and chromogranin. The CD10-negative, BCL6-positive, MUM1-positive profile supported activated B-cell-like DLBCL by the Hans algorithm. This case highlights the importance of a broad immunohistochemical panel in small nasopharyngeal biopsies and demonstrates how aberrant p63 expression can complicate distinction from epithelial malignancy.