Mandibular Follicular Lymphoma: A Rare Extranodal Presentation With Initial Facial Bone Involvement.

Follicular lymphoma is a common subtype of B-cell non-Hodgkin lymphoma, typically presenting with nodal involvement and, less frequently, in extranodal locations. Primary involvement of the mandible is extremely rare and is often mistaken for odontogenic or inflammatory pathologies, leading to delayed diagnosis. We present the case of a 73-year-old female patient with progressive swelling of the left hemimandible, associated with hypoesthesia of the ipsilateral lower lip. Computed tomography revealed an infiltrative soft tissue lesion with cortical bone erosion and involvement of the inferior alveolar canal. Flow cytometry identified a clonal population of CD20+, CD10+, and BCL2+ B cells, consistent with a diagnosis of follicular lymphoma. Staging with positron emission tomography demonstrated additional extranodal involvement, establishing the disease as Ann Arbor stage IV. The patient was proposed for systemic chemotherapy with rituximab, cyclophosphamide, vincristine, and prednisone, followed by maintenance with rituximab, showing marked clinical and functional improvement after the second treatment cycle. This case highlights the importance of considering lymphoproliferative disorders in the differential diagnosis of persistent mandibular masses. It also underscores the value of flow cytometry in evaluating complex oral presentations and emphasizes the role of a multidisciplinary approach for early diagnosis and effective treatment.