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Myxoid Pleomorphic Liposarcoma

Myxoid pleomorphic liposarcoma is an exceptionally rare, aggressive adipocytic neoplasm, typically occurring in children and adolescents. Myxoid pleomorphic liposarcoma shows mixed histological features of conventional myxoid liposarcoma and pleomorphic liposarcoma and lacks the gene fusions and amplifications of myxoid liposarcoma, atypical lipomatous tumor, and dedifferentiated liposarcoma.

Symptoms & Causes

Introduction

Myxoid pleomorphic liposarcoma is a very rare and aggressive type of cancer that primarily affects children and young adults. It combines features of two other liposarcoma types: myxoid liposarcoma and pleomorphic liposarcoma. Importantly, it lacks the specific genetic changes seen in those other types.

Reference
WHO Classification of Tumours Editorial Board. Soft tissue and bone tumours [Internet]. Lyon (France): International Agency for Research on Cancer; 2020 [cited 2024 09 11]. (WHO classification of tumours series, 5th ed.; vol. 3). Available from: https://tumourclassification.iarc.who.int/chapters/33.

Related Terminology
Acceptable: pleomorphic myxoid liposarcoma.

Subtype(s)
None

Symptoms

Myxoid pleomorphic liposarcoma generally manifests as a large, deep-seated soft tissue mass.

Localization

Myxoid pleomorphic liposarcoma has a predilection for the mediastinum (the area between the lungs in the chest). Other reported locations include the thigh, head and neck, perineum (the area between the anus and the scrotum or vulva), abdomen, and back.

Epidemiology

Myxoid pleomorphic liposarcoma occurs predominantly in children and young adults. Patient age in the large majority of published cases is < 30 years. There is a female predominance.

Etiology

Unknown

Diagnosis & Treatment

Staging

The American Joint Committee on Cancer (AJCC) and Union for International Cancer Control (UICC) TNM systems can be applied.

Pathogenesis

Myxoid pleomorphic liposarcoma has been associated with Li-Fraumeni syndrome, numerical chromosomal aberrations, and inactivation of the RB1 tumor suppressor gene.

Macroscopic appearance

Grossly, myxoid pleomorphic liposarcomas are non-encapsulated tumors with ill-defined margins.

Histopathology

Histologically, the tumors show variable proportions of myxoid liposarcoma-like areas, characterized by abundant myxoid matrix, scattered lipoblasts, relatively bland primitive round to oval cells, and a delicate curvilinear to plexiform capillary network. Lymphangioma-like myxoid pools can be observed. Pleomorphic spindle or ovoid cells with hyperchromatic nuclei may be scattered within the myxoid component, with a progressive transition into more-cellular, high-grade pleomorphic liposarcoma-like areas displaying severe cytological atypia, increased mitotic activity, atypical mitoses, pleomorphic lipoblasts, and occasional necrosis. Myxoid pleomorphic liposarcomas have a nonspecific immunophenotype.

Cytology

Not clinically relevant

Prognosis and prediction

Myxoid pleomorphic liposarcoma is an extremely aggressive tumor type with a high recurrence rate; metastasis to lung, bone, and soft tissue; and poor overall survival.

Clinical Features

Diagnostic molecular pathology

FISH studies have shown that myxoid pleomorphic liposarcoma lacks the FUS/EWSR1-DDIT3 gene fusions seen in conventional myxoid liposarcoma, as well as the MDM2 amplification present in well-differentiated/dedifferentiated liposarcoma.

Essential and desirable diagnostic criteria

Essential: distinctive admixture of relatively bland zones resembling conventional myxoid liposarcoma and much more cellular and atypical areas, resembling pleomorphic liposarcoma.

Desirable (in selected cases): absence of FUS/EWSR1-DDIT3 gene fusions and MDM2 amplifications.

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