Overview

Gastrointestinal stromal tumors — GISTs — are rare mesenchymal tumors of the gastrointestinal tract and represent the most common sarcoma of the digestive system. They may occur anywhere in the gastrointestinal tract, most commonly in the stomach and small intestine.

GISTs arise from, or are related to, the interstitial cells of Cajal, which are involved in gastrointestinal motility. Most cases occur in adults over the age of 50, while pediatric GISTs are rare and biologically distinct.

Clinical presentation may include:

• Gastrointestinal bleeding
• Anemia
• Abdominal pain or discomfort
• Early satiety
• Palpable abdominal mass
• Incidental finding during endoscopy or imaging

Small tumors may remain asymptomatic. Larger tumors may present with bleeding, obstruction, or rarely tumor rupture. The biological behavior of GIST ranges from very low-risk tumors to aggressive metastatic disease.

Importance of Specialized Care

GISTs are rare tumors and require management in specialized sarcoma or gastrointestinal oncology centers.

In Germany, optimal care is based on multidisciplinary and precision-driven assessment, including surgical oncology, medical oncology, gastroenterology, radiology, pathology, and molecular diagnostics.

Within the INDID Telemedicine network, GIST cases are evaluated in cooperation with specialized German partner centers and multidisciplinary tumor boards.

Specialized care is important because treatment decisions depend on:

• Tumor size
• Tumor location
• Mitotic rate
• Tumor rupture status
• Resectability
• Molecular mutation profile
• Risk of recurrence

Central pathology and molecular review are essential, because targeted therapy selection depends strongly on mutations such as KIT and PDGFRA.

Initial Diagnostic Workup and Risk Assessment

For most international patients, the diagnostic workup can be initiated locally and completed through INDID Telemedicine coordination without immediate travel to Germany.

Baseline clinical assessment includes:

• Medical history
• Physical examination
• Assessment of bleeding, anemia, abdominal pain, or obstruction
• Family history of GIST or related syndromes
• Evaluation of surgical fitness

Basic laboratory tests:

• Full blood count
• Liver function tests
• Renal function tests
• Coagulation profile
• Iron studies in patients with anemia

Tumor markers such as CEA, CA 19-9, and AFP are not diagnostic for GIST.

Diagnostic Evaluation

Imaging

High-quality imaging is essential for staging and treatment planning.

Recommended imaging includes:

• Contrast-enhanced CT scan of abdomen and pelvis
• CT chest in selected high-risk or metastatic cases
• MRI for rectal GIST, liver lesions, or when CT is contraindicated
• PET-CT in selected cases, especially for early response assessment during targeted therapy

For international patients, CT and MRI images should be transferred as complete DICOM files through secure digital systems. High-quality radiology is important to avoid incorrect staging, unnecessary travel, and inappropriate treatment planning.

The liver and peritoneum are the most common metastatic sites. Lymph node metastases are uncommon in adult GIST.

Endoscopy and Endoscopic Ultrasound

Endoscopy is useful for gastric, duodenal, esophageal, or rectal GISTs.

Endoscopic ultrasound — EUS — helps assess:

• Tumor size
• Layer of origin
• Depth of invasion
• Relationship to surrounding structures
• Possibility of EUS-guided biopsy

If available, endoscopic images and videos should be shared for multidisciplinary review.

Biopsy and Pathology

Biopsy is recommended when:

• Diagnosis is uncertain
• Neoadjuvant therapy is planned
• Disease is unresectable or metastatic
• Surgery would be extensive or organ-sacrificing

Preferred biopsy methods include:

• EUS-guided core needle biopsy
• Image-guided core biopsy of metastatic lesions when safe

Percutaneous biopsy of a primary resectable GIST should be avoided when there is risk of tumor rupture or peritoneal dissemination. This point was also emphasized in the previous SOP.

Pathology assessment should include:

• Tumor morphology
• Mitotic count
• Necrosis
• Tumor rupture status
• Resection margins after surgery
• Immunohistochemistry

Typical markers:

• KIT / CD117
• DOG1
• CD34
• SDHB in suspected SDH-deficient GIST

All pathology reports should be centrally reviewed. In selected cases, tissue blocks or slides should be reassessed in German reference pathology laboratories.

Molecular Testing

Molecular testing is mandatory for modern GIST management.

Recommended testing includes:

• KIT mutation analysis
• PDGFRA mutation analysis
• SDH assessment in selected cases
• Additional testing for KIT/PDGFRA wild-type GIST

Molecular results influence:

• Sensitivity to imatinib
• Need for alternative targeted therapy
• Neoadjuvant treatment planning
• Adjuvant therapy decisions
• Clinical trial eligibility

Multidisciplinary Treatment Planning

All GIST cases should be reviewed in a multidisciplinary tumor board at specialized German partner centers.

Treatment decisions are based on:

• Tumor size and location
• Symptoms
• Resectability
• Risk of rupture
• Mitotic rate
• Mutation profile
• Metastatic status
• Patient comorbidities and surgical risk

The tumor board defines whether the best approach is:

• Active surveillance
• Primary surgery
• Neoadjuvant targeted therapy
• Adjuvant therapy
• Systemic therapy for metastatic disease
• Local treatment of limited metastatic or progressive disease

Treatment Modalities

Active Surveillance

Selected very small, asymptomatic gastric GISTs with low-risk features may be followed without immediate surgery.

Surveillance may include:

• Endoscopy
• EUS
• CT or MRI
• Reassessment if growth or symptoms occur

Surgery

Surgery is the standard treatment for localized, resectable GIST.

Surgical principles include:

• Complete tumor removal
• Avoidance of tumor rupture
• Organ preservation when possible
• Negative margins where feasible
• No routine lymph node dissection in most adult GISTs

Minimally invasive surgery may be possible in selected cases. Large, fragile, invasive, or rupture-prone tumors should be treated in experienced centers.

Neoadjuvant Targeted Therapy

Neoadjuvant imatinib may be used when tumor shrinkage can reduce surgical morbidity.

Typical indications include:

• Large gastric GIST near the gastroesophageal junction or pylorus
• Duodenal GIST
• Rectal GIST
• Borderline resectable tumors
• Tumors at high risk of rupture

Mutation testing should be performed before starting neoadjuvant therapy.

Adjuvant Therapy

Adjuvant imatinib is recommended for patients with significant recurrence risk after complete resection of imatinib-sensitive GIST.

Usually, high-risk patients receive:

• Imatinib 400 mg daily
• Duration commonly 3 years

Adjuvant therapy decisions depend on:

• Tumor size
• Mitotic rate
• Tumor site
• Tumor rupture
• Mutation type

Systemic Therapy for Advanced Disease

For unresectable, recurrent, or metastatic GIST, systemic targeted therapy is the main treatment.

Common treatment sequence:

• First line: imatinib
• Second line: sunitinib
• Third line: regorafenib
• Fourth line: ripretinib

For PDGFRA D842V-mutant advanced GIST, avapritinib may be considered where available.

Treatment should be continued as long as there is clinical benefit and acceptable tolerance.

Follow-Up Strategy

Follow-up is individualized according to recurrence risk, tumor biology, and treatment status.

Typical follow-up includes:

• Clinical assessment
• CT or MRI abdomen and pelvis
• Laboratory monitoring during targeted therapy
• Evaluation of treatment side effects
• Review of symptoms suggesting recurrence

Suggested schedule:

• High-risk GIST: CT or MRI every 3–6 months initially
• Intermediate-risk GIST: imaging every 6–12 months
• Low-risk GIST: less intensive follow-up
• Very low-risk GIST: routine follow-up may not be necessary, although risk is not zero

The previous SOP also used a risk-adapted follow-up approach, with closer imaging for high-risk patients and less intensive follow-up for low-risk tumors.

Telemedicine Follow-Up – INDID

Patients treated in Germany usually do not need frequent travel for follow-up.

INDID Telemedicine provides:

• Remote review of CT, MRI, PET-CT, and endoscopy data
• Secure DICOM image transfer
• Central pathology and molecular reassessment
• Coordination with local oncologists and surgeons
• Monitoring of adjuvant or metastatic targeted therapy
• Early detection of recurrence or progression
• Tumor board reassessment in Germany when needed

This allows international patients to continue most follow-up care locally while maintaining access to German specialist expertise.

Key Strength of INDID Telemedicine Approach

INDID Telemedicine integrates:

• Cross-border diagnostic completion
• German sarcoma and gastrointestinal oncology expertise
• Centralized pathology review
• Molecular testing and mutation-based treatment planning
• Multidisciplinary tumor board decision-making
• Risk-adapted surgery and systemic therapy planning
• Structured remote follow-up
• Reduced unnecessary travel for international patients

This model is especially valuable for GIST because optimal treatment depends on the integration of imaging, pathology, molecular diagnostics, surgery, and targeted therapy.

Key Words

Gastrointestinal stromal tumor, GIST, KIT mutation, PDGFRA mutation, DOG1, CD117, SDH-deficient GIST, imatinib, sunitinib, regorafenib, ripretinib, avapritinib, neoadjuvant imatinib, adjuvant imatinib, mitotic rate, tumor rupture, sarcoma tumor board, molecular pathology, EUS-guided biopsy, DICOM imaging, INDID Telemedicine

References

1. Casali, P. G., Blay, J. Y., Abecassis, N., et al. Gastrointestinal stromal tumours: ESMO–EURACAN–GENTURIS Clinical Practice Guidelines for diagnosis, treatment and follow-up. Annals of Oncology. 2022;33:20–33.
2. Serrano, C., et al. 2023 GEIS Guidelines for gastrointestinal stromal tumors. Therapeutic Advances in Medical Oncology. 2023.
3. National Cancer Institute. Gastrointestinal Stromal Tumors Treatment — PDQ. Updated 2024.
4. Miettinen, M., Lasota, J. Gastrointestinal stromal tumors: pathology and prognosis at different sites. Seminars in Diagnostic Pathology. 2006;23:70–83.
5. von Mehren, M., et al. NCCN Guidelines Insights: Gastrointestinal Stromal Tumors. Journal of the National Comprehensive Cancer Network. 2022.