Biology and Management of Deep-seated Atypical Lipomatous Tumor of the Extremities

Abstract

Adipocytic neoplasms are frequently encountered in clinical practice. Atypical lipomatous tumor (ALT) is a locally aggressive but non-metastasizing adipocytic neoplasm that primarily occurs in the proximal extremities of middleaged to older adults. Histologically, ALT is divided into adipocytic (lipoma-like), sclerosing and inflammatory subtypes. The sclerosing subtype is an unfavorable prognostic factor for local recurrence. ALT is characterized by supernumerary ring and/or giant rod chromosomes. These rings and giant markers invariably contain amplified sequences originating from the long arm of chromosome 12, including the MDM2 protooncogene (MDM2) and cyclin-dependent kinase 4 (CDK4) gene. MDM2 and/or CDK4 nuclear immunopositivity is present in most cases. Confidently differentiating deep-seated ALT from deep-seated ordinary lipoma is often difficult on imaging. Moreover, the sclerosing subtype may mimic a higher grade liposarcoma. Detection of MDM2 amplification by fluorescence in situ hybridization would be helpful diagnostically for ALT in more difficult cases. The standard treatment for deep-seated ALT is surgery. Although there is no consensus on the best surgical approach for deep-seated ALT of the extremities, the use of marginal resection is acceptable to preserve musculoskeletal function. This review provides an overview of the current knowledge on the clinical and imaging characteristics, pathogenesis, histopathology, and management of deep-seated ALT of the extremities.Adipocytic tumors are the most common mesenchymal neoplasms of the extremities and represent a biologically and histologically diverse group. Many of these tumors are atypical lipomatous tumor (ALT) or ordinary lipoma (1). ALT is a locally aggressive mesenchymal neoplasm composed entirely or in part of mature adipocytic proliferation demonstrating at least focal nuclear atypia in both adipocytes and stromal spindle cells. Deep-seated ALT of the extremities shows no potential for metastasis unless it undergoes dedifferentiation. ALT is characterized by the presence of supernumerary ring and/or giant rod chromosomes. These rings and giant markers are composed, exclusively or partly, of amplified 12q13-15 material, including the MDM2 proto-oncogene (MDM2) and cyclindependent kinase 4 (CDK4) gene (2). MDM2 amplification is considered to represent one of the earliest events in the formation of ALT (3). In our experience, distinguishing ALT from ordinary lipoma can be challenging based on preoperative imaging features alone, especially if they occur in deep anatomical sites. Surgery is the mainstay of treatment for ALT. However, there is no consensus regarding the best surgical treatment for deep-seated ALT of the extremities. This review highlights the clinical and imaging characteristics, pathogenesis, histopathology, and management of deep-seated ALT of the extremities. Clinical CharacteristicsALT can occur at any age but has a peak incidence in the fifth to seventh decades of life, with no sex predilection (3). It most frequently occur...

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