Mesenchymal tumors


Topic Completed: 29 January 2021

Minor changes: 29 January 2021

Copyright: 2003-2021,, Inc.

PubMed search: leiomyosarcoma colonic [title]

Raul S. Gonzalez, M.D.
Page views in 2020: 1,265
Page views in 2021 to date: 1,400
Cite this page: Gonzalez RS. Leiomyosarcoma. website. Accessed September 21st, 2021.
Definition / general
  • Malignant smooth muscle tumor of colon
Essential features
  • Most older reports of colonic leiomyosarcomas were probably GIST
  • Small intestine and colon most common GI sites for leiomyosarcoma
Clinical features
Prognostic factors
Gross description
  • Intraluminal, bulging / polypoid mass measuring up to 25 cm
Microscopic (histologic) description
  • Resembles leiomyosarcoma at other sites: malignant smooth muscle cells with prominent nuclear atypia, coagulative necrosis and at least 1 mitosis per 10 high power fields
  • Rare examples have osteoclast-like giant cells (Arch Pathol Lab Med 2004;128:440)
Microscopic (histologic) images

Contributed by Raul S. Gonzalez, M.D.

Colonic leiomyosarcoma

Nuclear atypia

Numerous mitotic figures

Images hosted on other servers:

Well differentiated tumor

Moderately differentiated

Poorly differentiated

Positive stains
Negative stains
Molecular / cytogenetics description
  • Negative for KIT mutations
Sample pathology report
  • Transverse colon, resection:
    • Leiomyosarcoma (4.7 cm) (see comment)
    • Margins of resection unremarkable.
    • Three benign lymph nodes.
    • Comment: The tumor shows prominent nuclear atypia, numerous mitotic figures and regions of necrosis. Immunohistochemical stains for SMA and desmin are positive in the tumor. Leiomyosarcomas are rare in the colon and risk factors for progression in this location remain poorly defined.
Differential diagnosis
Board review style question #1

Which of the following properties is known to confer worse prognosis for colonic leiomyosarcomas?

  1. Mitotic rate > 1 per 10 high power fields
  2. Necrosis
  3. Patient age > 65 years
  4. Size > 5 cm
Board review style answer #1
D. Size > 5 cm

Comment Here

Reference: Leiomyosarcoma
Back to top
Image 01 Image 02