Liposarcoma Masquerading as Immunoglobulin G4-Related Disease

This case report highlights the challenge of differentiating between immunoglobulin G4 (IgG4)-related disease (IGRD) and liposarcoma, which have similar symptoms and serological markers. A 40-year-old woman presented with right upper-quadrant pain and a retroperitoneal mass. Initial biopsy indicated increased IgG4-positive cells, leading to an IGRD diagnosis. However, the mass grew, despite prednisone treatment, prompting a repeat biopsy that revealed well-differentiated liposarcoma. Liposarcoma should be considered in patients with retroperitoneal masses and elevated IgG4 levels. Surgical resection is the primary treatment, emphasizing the need for early identification and close monitoring. Confirming IGRD or ruling out other diagnoses through histopathologic analysis is vital.