Soft tissue

Smooth muscle



Last author update: 1 November 2012
Last staff update: 25 January 2022

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PubMed Search: Leiomyosarcoma [title] soft tissue

Vijay Shankar, M.D.
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Cite this page: Shankar V. Leiomyosarcoma-general. website. Accessed August 14th, 2022.
Definition / general
  • 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

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
Case reports
  • 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

Images hosted on other servers:

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

Images hosted on other servers:

Leg tumor

Retroperitoneal tumor

Thigh tumor


Microscopic (histologic) 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
Microscopic (histologic) images

AFIP images

Retroperitoneum smooth muscle morphology

Marked pleomorphism, 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 evident

Markedly pleomorphic, little evidence of smooth muscle differentiation

Multinucleated giant cells

Contributed by Mark R. Wick, M.D.

Deep soft tissue

Storiform growth


Images hosted on other servers:

Spindle cells arranged in interlacing bundles

Mitotic figures

Masson trichrome



Thigh, moderate nuclear pleomorphism

Pronounced nuclear pleomorphism

Foci of coagulative tumour cell


Epididymis tumor

Intravenous tumor

Tibial tumor

Mediastinal 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
Negative stains
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
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