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Soft tissue tumors

Smooth muscle

Myxoid leiomyosarcoma


Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 17 November 2014, last major update November 2012
Copyright: (c) 2003-2014, PathologyOutlines.com, Inc.

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

Definition
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● Defined as 50%+ myxoid stroma

Epidemiology
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● Rare; 75% women, median age 58 years, range 22-84 years

Clinical features
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● Usually affects chest, female genitalia (particularly uterus), head and neck, limbs
● 40% recur, 15% metastasize, 17% have tumor related deaths (Am J Surg Pathol 2000;24:927)
● Recur and metastasize regardless of mitotic count (which is deceptively low due to hypocellularity, Histopathology 1985;9:159)

Case reports
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● 20 year old woman with cystic mass of uterus (Acta Cytol 2000;44:415)
● 54 year old woman with mass of uterus (J Korean Med Sci 1998;13:559)
● 64 year old woman with liver tumor (Korean J Intern Med 2002;17:278)
● 85 year old woman with a unilateral nonulcerating, painless vulvar mass (Gynecol Oncol 2005;96:548)

Gross description
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● Large gelatinous mass
● Well circumscribed
● May have cystic change, necrosis and hemorrhage

Micro description
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● Invasive and infiltrative
● Fascicular, reticular, microcystic or resembling myxofibrosarcoma
● Spindled cells with smooth muscle features surrounded by abundant basophilic (myxomatous) material composed of hyaluronic acid
● Tumor cells have moderate to marked atypia but variable tumor cell necrosis
● May have focal epithelioid cells
● Usually low grade
● Deceptively low mitotic rates are due to hypocellularity

Micro images
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Figure 9         Various images

Cytology description
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● Resembles low to intermediate grade myxofibrosarcoma; diffusely granular myxoid stroma is accompanied by randomly distributed spindled or ovoid tumor cells, either solitary or in large cohesive cellular clusters; nuclei are round to ovoid, moderately pleomorphic and contain small / inconspicuous nucleoli (Cancer 2000;90:167, Acta Cytol 2000;44:415)
● Peritoneal washing of disseminated uterine tumor: uniformly dispersed spindly to polygonal epithelioid tumor cells focally linked by background matrix; spindled tumor cells attach to and radiate from branching capillary structures; occasional scattered signet-ring cells; the background mucoid substance is more conspicuous in cell block (Diagn Cytopathol 2002;27:47)

Cytology images
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Figures 7-9

Positive stains
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● Smooth muscle actin
● High MIB-1 index although low mitotic count
● Desmin (50%), CAM5.2 (25%), EMA (15%)

Negative stains
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● S100, CD34

Differential diagnosis
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Inflammatory myofibroblastic tumor: no destruction of muscle fascicles at tumor-muscle interface, no nuclear pleomorphism, no tumor necrosis, ALK1+, h-caldesmon+ (Pathol Int 2006;56:625)
Myxofibrosarcoma: cells are myofibroblast or lipoblast-like, also typical MFH areas, curvilinear vessels (thick walled with broad arc) with condensation of cells around vessels, incomplete fibrous septa, myxoid stroma; no smooth muscle differentiation
Myxoid chondrosarcoma: malignant chondocytes present
Myxoid leiomyoma: not infiltrative; nuclei are small and bland, no mitotic activity
● Other myxoid tumors: low grade fibromyxoid sarcoma, myxofibrosarcoma, myxoid liposarcoma, cellular myxoma, myxoid peripheral nerve sheath tumor

End of Soft tissue tumors > Smooth muscle > Myxoid leiomyosarcoma


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