📋 Key Information Summary
- Gastrointestinal Stromal Tumours (GIST) are the most common mesenchymal tumours of the gastrointestinal (GI) tract, arising from interstitial cells of Cajal.
- Over 80% of GIST harbour activating mutations in the KIT (c-KIT) proto-oncogene; 5-10% have PDGFRA mutations. A small subset are wild-type.
- Diagnosis relies on morphology and immunohistochemistry (IHC): CD117 (KIT) and DOG1 are the most sensitive and specific markers.
- Risk stratification for recurrence post-resection uses the National Institutes of Health (NIH) modified criteria, incorporating mitotic rate, tumour size, and location.
- Surgery with negative microscopic margins (R0) is the primary curative treatment for localised, resectable GIST.
- Imatinib (Glivec®) is the cornerstone of adjuvant therapy for high-risk disease and first-line treatment for unresectable or metastatic GIST.
- Adjuvant imatinib is typically given for 3 years for high-risk patients, based on significant overall survival benefit.
- Mutational testing of KIT and PDGFRA is recommended for all GIST, as it predicts response to tyrosine kinase inhibitors.
- Patients with exon 9 KIT mutations may benefit from higher dose imatinib (800 mg daily) in the metastatic setting.
- PDGFRA D842V mutation confers primary resistance to imatinib; avapritinib is the preferred first-line agent for this genotype.
- Multidisciplinary team (MDT) discussion at a specialist sarcoma centre is essential for all GIST management plans.
- Aboriginal and Torres Strait Islander patients may face barriers to timely diagnosis, MDT access, and continuous therapy; culturally safe care and support are critical.
Introduction & Australian Epidemiology
Gastrointestinal Stromal Tumours (GIST) are the most common mesenchymal neoplasms of the gastrointestinal tract, thought to originate from the interstitial cells of Cajal or their precursors. They can occur anywhere along the GI tract, but most commonly arise in the stomach (60%) and small intestine (30%).
In Australia, GIST account for approximately 400-500 new diagnoses annually. The median age at diagnosis is in the sixth decade, with a slight male predominance. Most GIST are sporadic, but a small proportion (<5%) are associated with heritable syndromes such as Neurofibromatosis Type 1 (NF1) and Carney-Stratakis syndrome.
Pathophysiology & Mutations
GIST are driven by gain-of-function mutations in receptor tyrosine kinases, leading to constitutive activation of downstream signalling pathways (e.g., PI3K/AKT, RAS/MAPK) that promote cell proliferation and survival.
| Mutation Gene | Frequency | Common Exons | Clinical Implication |
|---|---|---|---|
| KIT | ~80% | 11 (juxtamembrane), 9 (extracellular) | Sensitive to imatinib. Exon 9 mutations may require higher doses. |
| PDGFRA | 5-10% | 18 (D842V most common), 12 | D842V mutation: primary resistance to imatinib. Sensitive to avapritinib. |
| Wild-type | ~10-15% | SDH-deficient, NF1, BRAF | Generally resistant to imatinib. Require alternative approaches. |
Mutational analysis is now considered standard of care in Australia for all GIST, guiding prognosis and therapy selection. It is funded via Medicare when performed at an accredited laboratory.
Diagnosis & Immunohistochemistry
Diagnosis is based on histological assessment of a biopsy or resection specimen, with ancillary immunohistochemistry (IHC) and molecular testing.
Spindle cell (70%), epithelioid (20%), or mixed type. Accurate mitotic count (per 50 high-power fields) is critical for risk stratification.
- CD117 (KIT): Positive in ~95% of GIST.
- DOG1: Highly sensitive and specific; useful in CD117-negative GIST.
- Other markers (SMA, S-100, desmin) are typically negative but help exclude mimics.
Staging & Risk Stratification
For localised GIST, the primary goal of staging is to determine resectability and assess recurrence risk post-surgery. The AJCC/UICC TNM staging (8th edition) is used, but the modified NIH consensus criteria are more clinically useful for adjuvant therapy decisions.
Modified NIH Risk Stratification (Miettinen & Lasota)
| Risk Category | Tumour Size (cm) | Mitotic Rate (per 50 HPF) | Tumour Site |
|---|---|---|---|
| Very Low | < 2.0 | < 5 | Any |
| Low | 2.1 - 5.0 | < 5 | Any |
| Intermediate | < 5.0 | 6 - 10 | Gastric |
| 5.1 - 10.0 | < 5 | Gastric | |
| High | > 5.0 | > 5 | Any |
| > 10.0 | Any | Any | |
| Any | > 10 | Any | |
| > 2.0 | > 5 | Non-gastric |
Imaging: Staging CT (chest/abdomen/pelvis) is standard. PET-CT (MBS Item 61506, Authority Required) may be used for assessing response to imatinib or ambiguous CT findings.
Management (Surgery & Imatinib)
Surgery for Localised Disease
The goal is complete gross resection (R0) without tumour rupture. Lymphadenectomy is not required as nodal metastases are rare. Laparoscopic resection is acceptable for small gastric GIST.
Adjuvant Imatinib Therapy
Indicated for patients at significant risk of recurrence.
Advanced / Metastatic Disease
Imatinib 400 mg daily is first-line. For exon 9 KIT mutations, 800 mg daily may be considered. Regular imaging (CT 3-6 monthly) assesses response.
Special Populations
Aboriginal and Torres Strait Islander Health Considerations
While specific data on GIST incidence in Aboriginal and Torres Strait Islander populations is limited, broader inequities in cancer outcomes are well documented. A culturally safe approach is essential.
📚 References
- 1. Casali PG, Blay JY, Abecassis N, et al. Gastrointestinal stromal tumours: ESMO-EURACAN-GENTURIS Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2022;33(1):20-33.
- 2. National Comprehensive Cancer Network (NCCN). NCCN Clinical Practice Guidelines in Oncology: Soft Tissue Sarcoma. Version 2.2024.
- 3. Joensuu H, Eriksson M, Sundby Hall K, et al. Survival outcomes associated with 3 years vs 1 year of adjuvant imatinib for patients with high-risk gastrointestinal stromal tumors: an analysis of a randomized clinical trial after 10-year follow-up. JAMA Oncol. 2020;6(8):1241-1246.
- 4. Miettinen M, Lasota J. Gastrointestinal stromal tumors: review on morphology, molecular pathology, prognosis, and differential diagnosis. Arch Pathol Lab Med. 2006;130(10):1466-1478.
- 5. Blay JY, Kang YK, Nishida T, et al. Gastrointestinal stromal tumours. Nat Rev Dis Primers. 2021;7(1):22.
- 6. Cancer Council Australia Sarcoma Guidelines Working Party. Clinical practice guidelines for the management of sarcoma. Cancer Council Australia, Sydney. 2023.
- 7. Australian Institute of Health and Welfare (AIHW). Cancer in Aboriginal & Torres Strait Islander people of Australia. Cat. no. CAN 118. Canberra: AIHW. 2023.
- 8. Reichardt P, Blay JY, Boukovinas I, et al. Adjuvant treatment of GIST with imatinib: solid ground or still quicksand? A comment on behalf of the EORTC Soft Tissue and Bone Sarcoma Group, the Italian Sarcoma Group, the NCRI Sarcoma Clinical Studies Group (UK), the Japanese Study Group on GIST, the French Sarcoma Group, and the Spanish Group for Research on Sarcomas (GEIS). Eur J Cancer. 2009;45(1):11-14.
- 9. Demetri GD, von Mehren M, Blanke CD, et al. Efficacy and safety of imatinib mesylate in advanced gastrointestinal stromal tumors. N Engl J Med. 2002;347(7):472-480.
- 10. Therapeutic Goods Administration (TGA). Australian Public Assessment Report for Imatinib (as mesylate). Department of Health, Australian Government. 2022.
- 11. National Health and Medical Research Council (NHMRC). National Statement on Ethical Conduct in Human Research 2023 (Updated 2024). Canberra: NHMRC.