Subcutaneous Nodules as the Initial Presentation of Rare Primary Cutaneous Marginal Zone B-cell Lymphoma: Case Report

Abstract

Background: Primary cutaneous marginal zone B-cell lymphoma (PCMZL) is a rare subtype of extranodal marginal zone lymphoma that typically remains confined to the skin. While generally indolent with a favorable prognosis, its diagnosis can be challenging due to overlap with other cutaneous lymphoid proliferations.

Case Presentation: A 74-year-old man presented with longstanding subcutaneous nodules (>2 cm) on both cheeks, the submental region, and the right jaw, without overlying epidermal changes. Biopsies demonstrated a low-grade B-cell lymphoma with IgM expression and plasmacytic differentiation, and next-generation sequencing identified a MYD88 p.L265P mutation. Imaging revealed mediastinal lymphadenopathy, metabolically active nodes, and splenomegaly. Given the indolent course of PCMZL, observation was initially recommended. However, due to cosmetic concerns, rituximab therapy was initiated with a planned course of eight weekly infusions.

Discussion: PCMZL comprises approximately 25-30% of primary cutaneous B-cell lymphomas. It presents with erythematous or violaceous papules, plaques, or nodules, most often on the trunk and extremities. Accurate diagnosis requires integration of clinical, histopathologic, and molecular findings. Although prognosis is excellent, relapse occurs in up to 50% of patients. Management strategies vary and may include observation, surgical excision, radiotherapy, or systemic therapies such as rituximab. In this case, therapy was driven by patient preference, underscoring the importance of individualized care even in indolent disease.

Conclusion: PCMZL should be considered in the differential diagnosis of persistent subcutaneous nodules. This case emphasizes both the rarity of the disease and the role of patient-centered factors in guiding treatment.