Colon
Mesenchymal tumors
Leiomyosarcoma
Author: Raul S. Gonzalez, M.D.
Last author update: 29 January 2021
Last staff update: 29 January 2021
Copyright: 2003-2025, PathologyOutlines.com, Inc.
PubMed search: leiomyosarcoma colonic [title]
Table of Contents
Definition / general | Essential features | Terminology | Epidemiology | Sites | Etiology | Clinical features | Prognostic factors | Treatment | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Negative stains | Molecular / cytogenetics description | Sample pathology report | Differential diagnosis | Board review style question #1 | Board review style answer #1Cite this page: Gonzalez RS. Leiomyosarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/colontumorLMS.html. Accessed April 1st, 2025.
Definition / general
- Malignant smooth muscle tumor of colon
Essential features
- Rare, with poor prognosis
- Arises in muscularis propria (Mod Pathol 2015;28 Suppl 1:S47)
Terminology
- Most older reports of colonic leiomyosarcomas were probably GIST
Epidemiology
- Rare in colon; less common than GIST (Am J Surg Pathol 2000;24:1339)
Sites
- Small intestine and colon most common GI sites for leiomyosarcoma
Etiology
- May be a rare late effect of pelvic radiation (Hepatogastroenterology 2003;50:1933, Am Surg 1999;65:6)
Clinical features
- Adult patients often die of disease
- Tumors in infants may have more favorable prognosis (J Pediatr Surg 2004;39:1257)
Prognostic factors
- Tumor size > 5 cm suggests poor prognosis (Histopathology 2013;63:194)
Treatment
- Surgical resection, including of metastases (J Gastrointest Oncol 2015;6:E70)
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
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
- Gastrointestinal stromal tumor:
- Metastatic leiomyosarcoma:
- May require clinical correlation (South Med J 1997;90:1238)
Board review style question #1
Which of the following properties is known to confer worse prognosis for colonic leiomyosarcomas?
- Mitotic rate > 1 per 10 high power fields
- Necrosis
- Patient age > 65 years
- Size > 5 cm
Board review style answer #1
