Smooth Muscle Tumors of the Gut

Editorial note

This article presents cases of smooth muscle tumors of the gut with current management practices. Gastrointestinal “smooth muscle tumors” require classification with immunohistochemistry and, when relevant, molecular testing because gastrointestinal stromal tumor (GIST) is recognized as the most common mesenchymal neoplasm of the gastrointestinal tract, whereas true gastrointestinal leiomyoma and leiomyosarcoma are much less common.123

Introduction

Five gastrointestinal mesenchymal tumors managed at the University Hospital of the West Indies are presented. The cases are clinically instructive. Modern practice require routine use of CD117/KIT and DOG1 immunostaining, which now form part of standard evaluation for suspected GIST.23

Patients with gastrointestinal mesenchymal tumors may present with abdominal pain, gastrointestinal bleeding, anemia, obstruction, weight loss, or an incidental mass found on imaging or endoscopy. Contemporary epidemiology shows that GIST most often arises in the stomach, followed by the small bowel, with less frequent colorectal and esophageal involvement.23

Case summaries

Case I

A 57-year-old woman presented with right upper quadrant abdominal pain, intermittent melena, and an intra-abdominal mass with a hepatic lesion on imaging. At laparotomy, she was found to have a jejunal tumor with a hepatic metastasis, and the original pathology report described a leiomyosarcomatous tumor with a mitotic rate of 8 per 10 high-power fields.

Current description: A jejunal mesenchymal tumor with liver metastasis requires immunohistochemistry and specialist pathology review to distinguish metastatic GIST from true leiomyosarcoma, because morphology and mitotic count alone are insufficient for classification.234

Case II

A 63-year-old man presented with recurrent upper gastrointestinal bleeding and was found to have a 7 cm gastric mass treated by wedge excision. The original histology described interlacing bundles and whorls of smooth muscle fibers with hemorrhage, necrosis, and 2 mitoses per 10 high-power fields.

Current description: A bleeding gastric mesenchymal tumor is assessed with contrast-enhanced CT and pathology including CD117, DOG1, desmin, SMA, CD34, and S100, because true gastric leiomyosarcoma is rare and GIST is far more common.235

Case III

An 87-year-old man presented with recurrent upper gastrointestinal bleeding, anemia, and an epigastric mass. Gastroscopy showed a large ulcerated gastric lesion, and surgery identified a 13 cm gastric tumor with jejunal serosal and mesenteric seedings.

Current description: In current practice, this presentation prompts multidisciplinary review, modern contrast CT staging, and consideration of biopsy if neoadjuvant treatment were being considered. If confirmed to be GIST, tumor rupture or peritoneal spread strongly influence staging and systemic therapy planning.23

Case IV

A 77-year-old woman presented with recurrent episodes of intestinal obstruction, and surgery identified a 7 cm exophytic ileal tumor. The original pathology described a leiomyomatous tumor with 3 mitoses per 10 high-power fields.

Current description: Exophytic small-bowel mesenchymal tumors are a classic presentation for GIST, and diagnosis requires immunohistochemistry because low mitotic activity alone does not establish leiomyoma or exclude malignant potential.23

Case V

A 79-year-old woman presented with rectal bleeding, mucus passage, tenesmus, constipation, anorexia, weight loss, and synchronous rectal adenocarcinoma. The smooth muscle tumor measured 8 cm and showed mitotic activity greater than 15 per 10 high-power fields.

Current description: A rectal mesenchymal tumor is evaluated with pelvic MRI, expert pathology review, and careful distinction between rectal GIST and leiomyosarcoma because treatment planning, recurrence risk, and systemic options differ substantially between these entities.124

Discussion

Clinical presentation

Current guideline-supported evidence indicates that gastrointestinal mesenchymal tumors, especially GIST, most often present with abdominal pain, gastrointestinal bleeding, anemia, obstruction, or incidental detection during imaging or endoscopy.23 Metastatic disease at diagnosis is not universal but commonly involves the liver or peritoneum when present.3

Diagnostic evaluation

Contrast-enhanced CT is the standard first-line imaging study for suspected GIST because it defines tumor location, extent, and metastatic spread. MRI is particularly valuable for rectal lesions, while PET/CT is generally reserved for selected cases such as early response assessment during neoadjuvant therapy.23

Biopsy is not always required before surgery if imaging strongly suggests a clearly resectable GIST. However, tissue diagnosis is recommended when the radiologic diagnosis is uncertain, metastatic disease is suspected, or preoperative systemic therapy is being considered.23

Pathology and classification

Modern classification of gastrointestinal mesenchymal tumors depends on morphology, immunohistochemistry, and sometimes molecular analysis. For suspected GIST, a basic immunohistochemistry panel includes CD117, DOG1, actin, desmin, CD34, and S100, and molecular analysis of KIT and Platelet-Derived Growth Factor Receptor Alpha (PDGFRA) is strongly recommended because it can refine diagnosis, prognosis, and treatment selection.23

Pathology reporting for resected GIST includes anatomic site, tumor size, focality, mitotic activity expressed per 5 mm2, rupture status, margin status, and ancillary molecular data when available. This is a major change from earlier literature that relied mainly on mitotic counts per 10 or 25 high-power fields and broad labels such as “benign” or “malignant smooth muscle tumor.”3

True gastrointestinal leiomyosarcoma remains rare because many tumors historically classified as smooth muscle tumors are now classified as GIST. When leiomyosarcoma is present, immunohistochemistry helps confirm smooth muscle differentiation and exclude GIST.45

Treatment principles

For localized GIST, complete surgical resection with an intact pseudocapsule is the standard treatment. Organ-sparing wedge or segmental resection is generally preferred when feasible, and routine lymphadenectomy is usually unnecessary except in selected scenarios such as suspected nodal disease or specific rare subtypes.23

High-risk, imatinib-sensitive localized GIST should be considered for adjuvant imatinib, typically for 3 years. For locally advanced or anatomically difficult GIST, neoadjuvant imatinib may reduce surgical morbidity when guided by multidisciplinary review and appropriate molecular testing.23

Advanced GIST is not managed as a purely surgical disease. Contemporary care is genotype-directed and may involve imatinib, sunitinib, regorafenib, ripretinib, or avapritinib depending on the mutation profile and treatment line.23

For true gastrointestinal leiomyosarcoma, surgery remains the main local treatment, but evidence for adjuvant therapy is limited and management should be individualized in centers familiar with soft tissue sarcoma. Because these tumors are rare, current literature relies heavily on case reports and small series rather than robust GI-specific randomized trials.45

Conclusion

The surgical case series provide occasion for review of the modern management of smooth muscle gastrointestinal tumors through current pathology and sarcoma/GIST guidelines for the diagnostic taxonomy, investigation pathway, prognostic grading, and treatment recommendations.123

References

  1. British Sarcoma Group. “Gastrointestinal Stromal Tumour (GIST): British Sarcoma Group Clinical Practice Guidelines.” British Journal of Cancer, 2024. https://www.nature.com/articles/s41416-024-02672-0
  2. Casali, Paolo G., et al. “Gastrointestinal Stromal Tumours: ESMO-EURACAN-GENTURIS Clinical Practice Guidelines for Diagnosis, Treatment and Follow-Up.” Annals of Oncology 33, no. 1 (2022): 20-33. https://pubmed.ncbi.nlm.nih.gov/34560242/
  3. Serrano, César, et al. “2023 GEIS Guidelines for Gastrointestinal Stromal Tumors.” Therapeutic Advances in Medical Oncology 15 (2023): 17588359231192388. https://pmc.ncbi.nlm.nih.gov/articles/PMC10467260/
  4. “Diagnosis and Management of Sigmoid Leiomyosarcoma Presenting with Sigmoid-Rectal Intussusception.” Journal of Surgical Case Reports, 2024. https://academic.oup.com/jscr/article/2024/12/rjae795/7928271
  5. “Gastric Leiomyosarcoma: A Case Report and Literature Review.” 2025. https://pmc.ncbi.nlm.nih.gov/articles/PMC12594041/