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Soft Tissue Tumors Part 3
Muscle, Vascular, Nerve, Other
Myxoid leiomyosarcoma
Author: Nat Pernick, M.D, PathologyOutlines.com, Inc.
Revised: 11 August 2009, last major update - August 2009
Copyright: (c) 2002-2009, PathologyOutlines.com, Inc.
Leiomyosarcoma: general, cutaneous, epithelioid, myxoid, pleomorphic, rhabdoid features
Myxoid leiomyosarcoma
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
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● Limbs, female genitalia (particularly uterus), head and neck, chest
● 40% recur, 15% metastasize, 17% have tumor related deaths (AJSP 2000;24:927)
● Recur and metastasize regardless of mitotic count (which is deceptively low due to hypocellularity, Histopathology 1985;9:159)
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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Left: smooth muscle differentiation,
right: myxoid material splays
smooth muscle fibers
Cytology
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● Resembles low to intermediate grade myxofibrosarcoma; diffusely granular myxoid film 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)
● 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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Large cohesive fragment with background pink, Solitary, atypical tumor cells
granular and myxoid film (Diff-Quik) resemble myxofibrosarcoma (Pap)
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, myxoid liposarcoma, cellular myxoma, myxoid peripheral nerve sheath tumors)
End of Soft Tissue Tumors Part 3 - Muscle, Vascular, Nerve, Other > Myxoid leiomyosarcoma
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