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Uterus (excludes Cervix)

Stromal tumors

Malignant leiomyoblastoma

Reviewer: Mohamed Mokhtar Desouki, MD, PhD (see Reviewers page)
Revised: 22 August 2011, last major update August 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Definition
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● Rare but important tumor of uterus and broad ligament
● Recurs and metastasizes regardless of mitotic count

Terminology
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● Also called epithelioid leiomyosarcoma, clear-cell leiomyoma

Treatment
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● Hysterectomy, bilateral salpingo-oophorectomy and debulking
● Radio- and chemotherapy are not effective
● Hormonal therapy used in a few cases

Gross description
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● Gelatinous, well-circumscribed

Micro description
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● Invasive and infiltrative, highly myxomatous
● Rounded to polygonal shaped cells and mixtures of epithelioid and clear cells in a plexiform pattern
● Tumor cells have moderate to marked atypia, but variable tumor cell necrosis

Micro images
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Stomach tumor

Positive stains
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● High MIB-1 index, although mitotic count may be low
● Desmin, smooth muscle actin, vimentin, muscle specific actin (HHF35), h-caldesmon (focal staining), human smooth muscle myosin heavy chain (SM1 and SM2), non-muscle myosin heavy chain (SMemb), ER and PR

Negative stains
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● Keratin, EMA, CD34, c-kit, S100, myoglobin, myf4, HMB45

EM description
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● Immature smooth muscle differentiation that mimics mesenchymal cells of fetal uterus (Histopathology 2003;42:379)
● Many tumour cells do not exhibit specific differentiation
● Bundles of thin filaments with or without focal densities are present in scattered tumor cells
● Thin filaments are well developed
● Intermediate filaments and thin filaments are closely intermingled and occasionally form distinctive complexes with many irregular, dense body-like structures
● Mitochondria, rough endoplasmic reticulum and free ribosomes are common

Differential Diagnosis
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● Endometrial stromal sarcoma with smooth muscle metaplasia
● Uterine leiomyoma

End of Uterus > Stromal tumors > Malignant leiomyoblastoma

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