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Pleomorphic Rhabdomyosarcoma

Pleomorphic rhabdomyosarcoma is a high-grade pleomorphic sarcoma, usually of adults, composed of bizarre brightly eosinophilic polygonal, round, and spindle cells that display skeletal muscle differentiation.

Symptoms & Causes

Introduction

Pleomorphic rhabdomyosarcoma is an aggressive form of adult soft tissue cancer characterized by pleomorphic and multinucleated cells showing skeletal muscle features.

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
None

Subtype(s)
None

Symptoms

Patients present with rapidly growing, usually deep, variably painful soft tissue swelling.

Localization

These tumors arise in the deep soft tissue, most often in the lower extremity but also in the chest/abdominal wall, upper extremity, abdomen/retroperitoneum, and head and neck.

Epidemiology

These are tumors of adults and are most common in the sixth to seventh decades of life (mean age: ~72 years), occurring more frequently in men than in women, with an M:F ratio of 1.8:1.

Etiology

Unknown

Diagnosis & Treatment

Staging

See section Embryonal rhabdomyosarcoma.

Pathogenesis

Pleomorphic rhabdomyosarcomas have complex karyotypes with numerical and unbalanced structural changes but no recurrent structural alterations. Genome-wide surveys have identified recurrent losses of DNA (e.g., 10q23), gains (e.g., 1p22-p23), and amplifications. This copy-number pattern differs from that found in either alveolar or embryonal rhabdomyosarcoma. The genetic profiles of pleomorphic rhabdomyosarcomas are indistinguishable from those of undifferentiated pleomorphic sarcomas.

Macroscopic Appearance

Pleomorphic rhabdomyosarcomas are usually large, well-marginated tumors, with a pseudocapsule and a whitish or fleshy cut surface, often with necrosis.

Histopathology

The tumors are composed of sheets of large, atypical, and frequently multinucleated polygonal, spindled, or rhabdoid cells with eosinophilic cytoplasm. Tumors typically display strong desmin expression and often limited expression of MYOD1 and myogenin.

Cytology

Not clinically relevant

Prognosis and Prediction

These are highly aggressive sarcomas. The median survival was 7.3 months in the largest study to date, and about 80% of patients died of disease. Patients with superficial tumors (~20%) had a favorable outcome. Metastases to lungs are common.

Clinical Features

Diagnostic Molecular Pathology

Not clinically relevant

Essential and Desirable Diagnostic Criteria

Essential: pleomorphic cells with copious brightly eosinophilic cytoplasm; immunolabeling for desmin and myogenin.

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