Diagnostic and management challenges for MDM2-, CDK4-negative fatty tumors of the retroperitoneum

Background Neoplasms of the retroperitoneum that contain a major fat component may represent either benign entities, such as lipomas or angiomyolipomas, or malignancy such as liposarcoma. Distinguishing these diagnoses has important implications for management. While liposarcomas often stain positively for MDM2 and CDK4 proteins, absence of these markers can lead to diagnostic and management challenges. Methods We examined three cases in our institution of fat-containing masses of the retroperitoneum that lacked MDM2 and CDK4 markers to highlight the challenges in diagnosing and managing these cases. A thorough review of the literature examining radiologic and histologic features that can be used to determine that diagnosis was conducted and summarized. Results The three cases we present represent the three main diagnostic entities that can be found in among fatty tumors of the retroperitoneum: lipoma, angiomyolipoma, and liposarcoma. While radiologic features and analysis of histology helped to inform management, these cases in conjunction with the literature also illustrate the limitations of the diagnostic work up and importance also factoring the biologic behavior of the tumor in its management. Conclusion Fat-containing tumors of the retroperitoneum that do not stain for MDM2 or CDK4 can pose a diagnostic challenge. Assessing radiologic and pathologic features in conjunction with the biologic behavior of these tumors should inform their management.