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: 11 August 2020

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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. http://www.pathologyoutlines.com/topic/uteruslms.html. Accessed November 26th, 2020.
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

Leiomyosarcoma and adenocarcinoma

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 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 answer #2
D. Leiomyosarcoma

Comment Here

Reference: Leiomyosarcoma
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