Smooth muscle tumors


Editorial Board Member: Jennifer A. Bennett, M.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Paulette Mhawech-Fauceglia, M.D.

Topic Completed: 5 December 2019

Minor changes: 20 September 2021

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PubMed search: Leiomyosarcoma[TI] uterus[TI] pathology full text[sb]

Paulette Mhawech-Fauceglia, M.D.
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Cite this page: Mhawech-Fauceglia P. Leiomyosarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/uteruslms.html. Accessed December 6th, 2021.
Definition / general
  • Rare tumor derived from smooth muscle
  • Most common uterine sarcoma
Essential features
  • Uterine leiomyosarcoma
ICD coding
  • ICD-10: C55 - malignant neoplasm of uterus, part unspecified
  • Uterus
Clinical features
  • Usually discovered incidentally during hysterectomy for fibroids (Am J Obstet Gynecol 2019;220:179.e1)
  • Symptoms include abnormal vaginal bleeding and those related to a pelvic mass
  • 70 - 75% of patients present with stage I and II disease
Radiology description
  • CT: might show irregular central zones of low attenuation, suggesting extensive necrosis and hemorrhage
  • MRI: has been speculated that an irregular margin of leiomyoma could be suggestive of sarcomatous transformation but it is not specific (J Magn Reson Imaging 2019;49:e282)
Radiology images

Images hosted on other servers:

Very large mass

Lung metastasis

Prognostic factors
  • Even with tumor confined to uterus, it is considered aggressive
  • There is no consensus on how to grade; therefore, it is not advised to grade as low or high grade
  • Most powerful prognostic factor is tumor stage; however, other factors such as tumor size, mitotic count and percentage of necrosis have been suggested to predict patient's outcome (Curr Probl Cancer 2019;43:283)
Case reports
  • Total abdominal hysterectomy, bilateral salpingo-oophorectomy for postmenopausal females and those with metastatic disease
  • Total abdominal hysterectomy without bilateral salpingo-oophorectomy for premenopausal females
  • Lymph node sampling is unnecessary, as < 3% of patients will have lymph node involvement
  • Adjuvant chemotherapy / radiotherapy has not been proven beneficial (Sarcoma 2019;2019:3561501)
  • Hormonal therapy may be an option in hormone receptor positive tumors
Clinical images

Images hosted on other servers:

Very large mass

Gross description
  • Bulky, fleshy tumor invading into myometrial wall or polypoid tumor projecting into lumen
  • Often hemorrhagic or necrotic
  • Grossly appears invasive / infiltrative
  • Very large with a mean diameter of 10 cm
  • Myxoid leiomyosarcoma:
    • Gelatinous cut surface
    • May appear well circumscribed
Gross images

Images hosted on other servers:

Large mass

Frozen section description
  • Frozen section is not recommended for diagnosis
Microscopic (histologic) description
  • Conventional / spindle cell type:
    • Diagnosis requires 2 of 3 histologic features (marked cellular atypia, > 10 mitoses/10 high power fields and tumor cell necrosis)
    • Cellular tumor comprised of spindled / fascicular cells with moderate to severe pleomorphism
    • Mitotic index is typically high and atypical mitoses are often seen
    • Often has an infiltrative border
    • Multinucleated cells may be seen
  • Myxoid leiomyosarcoma:
    • Diagnosed based on presence of any cytologic atypia, tumor cell necrosis or > 1 mitosis/10 high power fields (Am J Surg Pathol 2016;40:285)
    • Hypocellular tumor with abundant myxoid stroma
  • Epithelioid leiomyosarcoma:
    • Diagnosed based on the presence of moderate to severe cytologic atypia or tumor cell necrosis or ≥ 4 mitoses/10 high power fields
    • Round or polygonal cells with eosinophilic or clear cytoplasm
    • Tumor cells arranged in sheets, nests or cords
Microscopic (histologic) images

Contributed by Paulette Mhawech-Fauceglia, M.D.

Hypercellular tumor

Nuclear atypia

Numerous mitoses


Positive stains
Negative stains
Molecular / cytogenetics description
  • Complex numerical and structural chromosomal aberrations suggesting that chromosomal instability is the hallmark of uterine smooth muscle tumors
  • TP53 (33%), ATRX (26%), MED12 (21%) mutations (PLoS Genet 2016;12:e1005850)
  • NR4A3-PGR fusion or PGR rearrangements have been documented in 35% of epithelioid leiomyosarcomas (Am J Surg Pathol 2019;43:810)
  • PLAG1 rearrangements have been identified in ~25% of myxoid leiomyosarcomas (Am J Surg Pathol 2019;43:382)
Sample pathology report
  • Uterus, total abdominal hysterectomy:
    • Uterine leiomyosarcoma (see synoptic report)
Differential diagnosis
Board review style question #1
Which of the following molecular alterations has been reported in uterine leiomyosarcomas?

  1. ALK fusions
  2. BCOR fusions
  3. JAZF1 fusions
  4. TP53 mutations
  5. TSC2 mutations
Board review style answer #1
D. TP53 mutations

Comment Here

Reference: Leiomyosarcoma
Board review style question #2
A uterine mass in a 50 year old woman has a tumor shown in the photomicrograph which expresses SMA, ER, PR and caldesmon and is negative for CD10 and CD117 / KIT. What is your diagnosis?

  1. Endometrial stromal sarcoma
  2. Gastrointestinal stromal tumor
  3. High grade endometrial adenocarcinoma
  4. Leiomyosarcoma
Board review style answer #2
D. Leiomyosarcoma

Comment Here

Reference: Leiomyosarcoma
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