S3361 Liposarcoma Masquerading as IgG4-Related Disease

Abstract

Introduction: IgG4-related disease (IGRD) is characterized by lymphoplasmacytic tissue infiltration by IgG4-positive plasma cells and small lymphocytes and is known to involve multiple organs, sometimes simultaneously.1 Retroperitoneal involvement is common with IGRD, often presenting as mass-like lesions and fibrosing disease such as retroperitoneal fibrosis2 and sclerosing mesenteritis3. While there is no established association, very few cases have been reported in literature about strong IgG4 positivity and sarcomas.3,4 Investigation usually warrants biopsy, as imaging studies and serologies cannot differentiate between IGRDs and sarcomas. We present a case of an aggressive liposarcoma mimicking IGRD. Case Description/Methods: A 40-year-old female presented with right upper quadrant (RUQ) pain for 3 months. Patient was hemodynamically stable with physical exam demonstrating fullness and tenderness in RUQ. CT abdomen revealed a 12.9x11.8x8.7 cm heterogenous macro-lobulated mass located below the inferior hepatic border in the retroperitoneal space and hepatorenal recess (Figure A). CT guided biopsy of the mass revealed increased IgG4-positive cells identified by immunohistochemical studies, however, FISH MDM2 amplification studies were inconclusive. Patient’s serum IgG4 levels were elevated, and she was started on prednisone therapy. At 2 month follow-up, the patient’s serum IgG4 levels had decreased but upon physical examination, the mass had increased in size and was firmer. Decision was made to repeat CT-guided biopsy, wherein MDM2 amplification studies revealed that the mass was consistent with well-differentiated liposarcoma (Figure B). She underwent liposarcoma resection, lymph node dissection, and right nephrectomy (adherent to the mass). Histopathologic analysis revealed a final diagnosis of stage I well-differentiated liposarcoma. Patient now follows for surveillance of her liposarcoma. Discussion: IGRD and liposarcoma can have common initial presentations and at times overlapping serological markers such as IgG4 levels, which necessitates histopathologic analysis for confirmation of the disease. In addition, raised IgG4 levels are not specific and can be elevated in infections and autoimmune conditions5. Our case emphasizes the importance of considering liposarcomas in retroperitoneal masses with elevated IgG4 levels, as they can mimic IGRD. A repeat biopsy should be considered if the initial diagnosis is doubtful, or patient responds poorly to corticosteroids.Figure 1.: A) Coronal view of the CT scan showing a macrolobulated heterogenous mass measuring 10.6x10.5x14.1cm, B) MDM2 expression of mass using FISH.