Title : IgG4-related sclerosing mastitis: A rare breast cancer mimicker with major diagnostic implications
Abstract:
Background: IgG4-related sclerosing mastitis (IgG4-RSM) is an exceptionally rare manifestation of IgG4-related disease that can closely mimic breast carcinoma or lymphoma. Because imaging findings are frequently suspicious and nonspecific, affected patients may undergo extensive diagnostic procedures or surgery before the correct diagnosis is established. We aim to define the key clinical, radiological, and pathological features of IgG4-RSM and highlight the diagnostic clues that may prevent overtreatment.
Methods: A systematic literature search was performed using terms related to IgG4, mastitis, sclerosing disease, and breast involvement. Eligible case reports and case series were evaluated for presentation, imaging, histopathology, IgG4 immunohistochemistry, serum IgG4 status, associated systemic disease, treatment, and clinical outcome.
Results: IgG4-RSM most commonly presented as a painless breast mass and was frequently classified as BI-RADS 4 or 5, making radiological distinction from malignancy unreliable. Histopathological examination consistently emerged as the decisive diagnostic step, typically demonstrating dense lymphoplasmacytic inflammation, fibrosis, and increased IgG4-positive plasma cells. Classical features of IgG4-related disease, including storiform fibrosis and obliterative phlebitis, were not uniformly present, while serum IgG4 could remain normal, limiting the value of serology alone. Breast involvement was identified both as an isolated process and as part of multisystem IgG4-related disease. Corticosteroid therapy generally produced favourable clinical and radiological responses, whereas surgery was mainly undertaken when malignancy could not be confidently excluded.
Conclusions: IgG4-RSM represents a rare but clinically important breast cancer mimic. Awareness of this entity and early integration of morphology, IgG4 immunohistochemistry, and systemic assessment may reduce diagnostic error, avoid unnecessary extensive surgery, and guide patients toward appropriate medical treatment.
