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Leiomyosarcoma of Bone

Leiomyosarcoma (LMS) of bone is a primary malignant neoplasm of bone showing smooth muscle differentiation.

Symptoms & Causes

Introduction

Leiomyosarcoma of bone is a rare malignant tumor that shows smooth muscle differentiation. It commonly affects the lower extremity around the knee but can also occur in other bones.

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 typically report pain and occasionally present with pathological fracture. Metastatic disease from extraosseous primary lesions (uterus, bowel, soft tissue) should be excluded, as this is more common than primary LMS of bone.

Localization

Most lesions occur in the lower extremity around the knee (distal femoral or proximal tibial metaphysis), followed by the craniofacial skeleton.

Epidemiology

There is a wide age distribution (9–87 years), with a peak incidence in the fifth decade of life and a slight male predominance.

Etiology

A small subset of LMSs of bone are associated with prior exposure to radiation therapy or bone infarcts. LMS of bone related to EBV infection in immunocompromised patients has also been reported.

Diagnosis & Treatment

Staging

Staging is according to bone sarcoma protocols.

Pathogenesis

Similar to deep soft tissue LMSs, intraosseous lesions show genomic losses and absence of phosphorylated RB1.

Macroscopic Appearance

The lesions vary widely in size. On cut surface, they show a tan, fleshy, creamy appearance, with obvious areas of necrosis.

Histopathology

The lesions resemble LMSs from other locations, with cells arranged in long, intersecting fascicles, growing in an infiltrative pattern. The tumor cells have fibrillary, eosinophilic cytoplasm and elongated, cigar-shaped nuclei with blunted ends. The tumors are associated with variable degrees of necrosis, nuclear pleomorphism, and mitotic activity.

Cytology

Not clinically relevant

Prognosis and Prediction

Histological grade correlates with clinical outcome. High-grade lesions are highly aggressive, with a high index of distant spread (often to the lung) and a 5-year disease-free survival rate of less than 50%.

Clinical Features

Diagnostic Molecular Pathology

Not clinically relevant

Essential and Desirable Diagnostic Criteria

Essential: bone tumor with compatible imaging; exclusion of other primary sites; intersecting fascicles of fusiform cells with eosinophilic fibrillary cytoplasm and elongated cigar-shaped nuclei, with variable nuclear pleomorphism; SMA and desmin and/or h-caldesmon immunoreactivity.

Desirable: positivity for ER or PR in female patients, suggesting a primary uterine origin.

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