CDK4 and soft tissue sarcoma: Well-differentiated liposarcoma (WDLPS) is a locally aggressive soft tissue sarcoma characterized by the amplification of MDM2 and/or CDK4. IgG4-related disease (IgG4-RD) is a rare fibroinflammatory disease characterized by elevated serum IgG4 levels and histologically fibrous tissues with IgG4-positive immune cell infiltration.