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Soft tissue tumors

Smooth muscle


Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 23 February 2013, last major update November 2012
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

Leiomyosarcoma: see also cutaneous, epithelioid, myxoid, pleomorphic, rhabdoid features


● Smooth muscle tumor with atypia plus either mitotic activity, tumor cell necrosis or size > 10 cm
● 10% of adult soft tissue sarcomas
● Variants are described separately above


Skin/subcutis: see cutaneous variants above; better survival than retroperitoneal tumors
Retroperitoneum: third most common retroperitoneal sarcoma after liposarcoma and MFH; usually women, 5 year survival is only 29% (Stanford University)
Immunocompromised patients: associated with EBV in HIV patients; may be multifocal


● Usually extremities
● Often arises from large vessels (Am J Surg Pathol 2002;26:14), most commonly inferior vena cava, saphenous vein, femoral vein, pulmonary artery, femoral artery
● Also occurs in retroperitoneum, superficial or deep soft tissues, rarely in bone, breast, colon, epididymis, mediastinum

Case reports

● 8 year old girl with oral cavity tumor (J Cancer Res Ther 2012;8:282)
● 26 year old man with EBV+ tumor after heart transplantation (Am J Surg Pathol 2000;24:614)
● 54 year old man with tumor of inferior vena cava (Arch Pathol Lab Med 2003;127:e423)
● 58 year old man with mediastinal tumor (Korean J Thorac Cardiovasc Surg 2012;45:192)
● 69 year old man with tumor of internal jugular vein (World J Surg Oncol 2008;6:113)
● 70 year old man with 25 cm epididymis mass (Case Rep Urol 2012;2012:236320)

Treatment and prognosis

● Excision with clear margins (enucleation is inadequate treatment)
● Often recurs locally or metastasizes
● Lung is common site of metastasis, lymph nodes are uncommon site
Poor prognostic factors: retroperitoneal, mesenteric or other deep location, size > 5 cm, age > 62 years, high grade, tumor disruption by prior incisional biopsy or incomplete excision (Cancer 2007;109:282), possibly nuclear c-myc expression (Mod Pathol 2009;22:1432)
● In extremities, poor prognostic factors are large size and high mitotic rate; best treatment is wide surgical excision plus adjuvant radiation therapy (Eur J Surg Oncol 2004;30:565)

Clinical images

12 cm tibial tumor

Oral cavity tumor

Epididymis mass (25 cm)

Internal jugular vein

Gross description

● Low grade tumors are hard masses and resemble leiomyomas, with white whorled cut surface
● High grade tumors are large, soft, often with necrosis, hemorrhage and cystic degeneration
● May project into lumen of major vessels or be intramural

Gross images

Leg tumor #1


Retroperitoneal tumor

Thigh tumor


Micro description

● Fascicular growth pattern (bundles intersect at right angles)
● Tumor cells merge with blood vessel walls
● Palisading of spindle cells with eosinophilic fibrillary cytoplasm, focal granularity
● Nuclei are cigar-shaped and blunt-ended with variable atypia, often with cytoplasmic vacuoles at both ends of nuclei (unlike neural lesions)
● Mitotic figures are common
● May have hemangiopericytoma-like vasculature, nuclear palisading, myxoid change, osteoclast-like giant cells, some may show extensive pleomorphism mimicking MFH
● Often infiltrates into adjacent tissue
● See also variants above

Malignant criteria by site

Soft tissue: 1-2 MF/10 HPF and deep
Skin/subcutaneous: 2 MF/10 HPF is definitive, 1 MF/10 HPF if consistent in all fields
Retroperitoneum: 5 MF/10 HPF is definitive, or 1-4 MF/10 HPF plus necrosis plus size > 7.5 cm
Vascular: 1-4 MF/10 HPF plus large size plus necrosis
● Diagnose as tumor of uncertain malignant potential (UMP) if mitotic figures are fewer than above or focal

Micro images

Oral cavity tumor

Thigh tumor

Retroperitoneum smooth muscle morphology

Marked pleomorphism and no identifiable smooth muscle

Uncertain malignant potential: 8 cm retroperitoneal tumor with bland cells and < 1 MF/10 HPF

Malignant based on low power pleomorphism

Pleomorphism and smooth muscle differentiation are evident

Markedly pleomorphic, little evidence of smooth muscle differentiation

Multinucleated giant cells

Intravenous tumor

Internal jugular vein tumor

Inf vena cava tumor: cytology, H&E, smooth muscle actin

Tibial tumor

Mediastinal tumor

Epididymis tumor

Cytology description

● Fascicles with an mixture of dispersed cells or stripped nuclei
● Most cells are spindled with elongated, blunt-ended, segmented or fusiform nuclei or round/polygonal with round or indented nuclei
● Also pleomorphic cells, occasionally intranuclear vacuoles, mitoses and osteoclast-like giant cells (Diagn Cytopathol 2006;34:597)

Positive stains

● HHF35 (90%), alpha-smooth muscle actin (90%), vimentin, desmin (75%, Cancer 2009;115:4186)
● H-caldesmon (Am J Clin Pathol 2000;113:663)
● PTAH (stains myofibrils), keratin (30%), ER (usually in uterine and female retroperitoneal tumors), S100 (occasionally weak staining), EMA (may be focal), occasionally CD34

Negative stains

● CD117

Electron microscopy description

● Some smooth muscle features, including cytoplasmic filaments with focal densities (also present in myofibroblasts), pinocytotic vesicles, thick basal lamina

Molecular / cytogenetics description

● Often complex karyotypes with no consistent aberrations

Differential diagnosis

Dedifferentiated liposarcoma: usually trunk, better prognosis, well differentiated component present, MDM2 and CDK4 amplification (Am J Surg Pathol 2007;31:1557)
Leiomyoma: no/rare mitotic activity, no/minimal atypia, small size, no hemorrhage, no necrosis

End of Soft tissue tumors > Smooth muscle > Leiomyosarcoma-general

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