p16 Expression in Fat Necrosis: A Potential Diagnostic Pitfall in the Evaluation of Differentiated Adipocytic Neoplasms

We describe a case of a large retroperitoneal adipocytic mass occurring in a 27-year-old male, which was clinically and radiologically in keeping with WDL. Histologically this was a differentiated adipocytic neoplasm with prominent fibrous septa and fat necrosis, more suggestive of retroperitoneal lipoma. Immunohistochemistry showed diffuse, strong nuclear expression of p16 in the areas of fat necrosis. However, CDK4 was negative and the lesion lacked evidence of MDM2 amplification with FISH. Diffuse expression of p16 in areas of fat necrosis in large or deep lipomas highlights the potential for diagnostic misinterpretation as well differentiated liposarcoma, and we therefore emphasize that p16 immunohistochemistry should always be interpreted as part of a panel with CDK4 +/– MDM2 in the differential diagnosis of WDL and lipoma.
Source: International Journal of Surgical Pathology - Category: Pathology Authors: Tags: Pitfalls in Pathology Source Type: research