Extranodal Marginal Zone B-cell Lymphoma Presenting as a Painless Buccal Mass in the Masticator Space

Extranodal marginal zone B-cell lymphoma (EMZL, mucosa-associated lymphoid tissue type) is an indolent non-Hodgkin lymphoma that only rarely arises in deep facial spaces. Primary masticator-space involvement is particularly uncommon and can mimic benign buccal soft-tissue lesions. We report a 67-year-old woman with a 4-year history of a painless, slowly enlarging left cheek mass. Examination showed a soft, mobile 3-cm buccal swelling with normal overlying skin and no intraoral lesion. Contrast-enhanced computed tomography demonstrated an infiltrative soft-tissue mass measuring 3.1 × 1.5 × 3.5 cm, centered in the left masticator space, with effacement of fat planes between the masseter, pterygoid, and temporalis muscles. Intraoral incisional biopsy revealed a dense infiltrate of small-to-medium CD20-positive, Bcl-2-positive B cells, with a CD5, CD10, CD23, Bcl-6-negative immunophenotype and follicular colonization on CD21 staining, consistent with EMZL. A multidisciplinary tumor board recommended involved-site radiotherapy to the masticator space combined with rituximab-based immunotherapy. This case represents a rare example of primary EMZL arising in the masticator space, which highlights the need to include lymphoma in the differential diagnosis of persistent head and neck masses, to obtain tissue diagnosis for infiltrative head and neck lesions and to coordinate organ-preserving treatment through multidisciplinary care.