Aggressive Mandibular Plasmablastic Lymphoma in an HIV-Negative Patient: Clinicopathologic and Immunophenotypic Insights From a Rare Oral Case.

Plasmablastic lymphoma (PBL) is a rare and highly aggressive subtype of diffuse large B-cell lymphoma characterized by plasmacytic differentiation and a distinct immunophenotypic profile. It is most frequently associated with human immunodeficiency virus (HIV) infection and typically involves the oral cavity. However, PBL may also occur in immunocompetent individuals, representing a diagnostic and clinical challenge. This report describes a rare case of PBL affecting the mandible of an HIV-negative patient who presented with a rapidly progressive ulcerated oral lesion. Histopathological examination revealed a diffuse proliferation of large atypical cells with plasmablastic morphology and a high mitotic rate. Immunohistochemical analysis demonstrated strong expression of plasma cell markers, including CD138 and MUM1, along with negativity for conventional B-cell markers such as CD20 and CD79a. The Ki-67 proliferation index was approximately 90%, confirming the aggressive biological behavior of the neoplasm. Based on these findings, a diagnosis of PBL was established. Despite prompt referral for oncologic management and initiation of chemotherapy, the disease showed rapid progression with an unfavorable outcome. This case highlights the importance of including PBL in the differential diagnosis of aggressive oral lesions, even in HIV-negative and immunocompetent patients, and emphasizes the critical role of histopathological and immunohistochemical evaluation for accurate diagnosis.