Surgical Pathology Criteria

Leiomyosarcoma of Deep Soft Tissue, Retroperitoneum, Mesentery and Omentum

Differential Diagnosis

 

In the deep soft tissue:

Leiomyoma (requires all below) Smooth Muscle Tumor of Uncertain Malignant Potential (used for any of below) Leiomyosarcoma (requires any one of below)
Cytologically bland   Cytologic pleomorphism or atypia
<1 mitotic figure / 50 HPF Bland but 1-4 mitotic figures / 50 HPF >4 mitotic figures / 50 HPF
No tumor cell necrosis Multiple recurrences but lacking other atypical features Coagulative tumor cell necrosis

Malignant Fibrous Histiocytoma Leiomyosarcoma of Deep Soft Tissue, Retroperitoneum, Mesentery and Omentum
Pleomorphic, histologically undifferentiated Elongate or spindled eosinophilic cytoplasm
Lacks abundant desmin and caldesmon Typically desmin or caldesmon positive
MFH may be actin positive
The distinction between MFH and high grade leiomyosarcoma is not clinically important and may be one of convention

Dedifferentiated Liposarcoma Leiomyosarcoma of Soft Tissue
Evidence of concurrent or antecedent atypical lipomatous tumor No evidence of atypical lipomatous tumor
Foci of smooth muscle cells may be present in dedifferentiated liposarcoma

Inflammatory Myofibroblastic Tumor Leiomyosarcoma of Soft Tissue
Usually <14 years, rare >30 years Rare under 12 years
Chronic inflammation usual Infrequent inflammation
Rare inflammatory leiomyosarcoma exhibits a regular fascicular pattern

Gastrointestinal Stromal Tumor (GIST)

Parasitic Leiomyoma

Mesenteric Fibromatosis Leiomyosarcoma of Deep Soft Tissue, Retroperitoneum, Mesentery and Omentum
Desmin infrequent Desmin or caldesmon usually positive
Beta catenin 90% positive Beta catenin negative
Scant cytoplasm Elongate eosinophilic cytoplasm
Cytologically bland May be cytologically atypical
Stroma diffusely myxoid Stroma infrequently myxoid

Angiomyolipoma/PEComa Leiomyosarcoma of Deep Soft Tissue, Retroperitoneum, Mesentery and Omentum
May have fatty component Lacks intrinsic fat
May have abnormal vascular component Lacks distinctive large abnormal vessels
HMB45, MelanA positive HMB45, MelanA negative

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