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.