What labs should be checked for GIST patients?

Routine Laboratory Tests for GIST Patients

For patients with gastrointestinal stromal tumors (GISTs), routine laboratory monitoring should include complete blood count, liver function tests, and molecular genetic testing for KIT and PDGFRA mutations. 1

Initial Diagnostic Workup

Essential Laboratory Tests

• Complete blood count (CBC)
• Comprehensive metabolic panel including:
  • Liver function tests (ALT, AST, ALP, GGT, total bilirubin, direct bilirubin)
  • Renal function tests (BUN, creatinine)
  • Electrolytes
  • Glucose

Molecular Testing

• KIT mutation analysis (exons 9,11,13,17)
• PDGFRA mutation analysis (especially exon 18 D842V mutation)
• For KIT/PDGFRA wild-type tumors:
  • SDHB expression (immunohistochemistry)
  • If SDHB-negative, test for SDH mutations
  • Consider testing for BRAF, KRAS, NRAS mutations
  • Consider testing for NTRK fusions

Monitoring During Treatment

For Patients on Tyrosine Kinase Inhibitors (TKIs)

• CBC every 2-4 weeks for first 3 months, then monthly
• Liver function tests every 2-4 weeks for first 3 months, then monthly
• Thyroid function tests (TSH) every 3-6 months 2
• Left ventricular ejection fraction assessment at baseline and periodically (especially for patients on sunitinib) 2
• Blood pressure monitoring (especially for patients on sunitinib) 2

Laboratory Abnormalities to Monitor

• Neutropenia (occurs in up to 53% of patients on sunitinib) 2
• Thrombocytopenia (occurs in up to 38% of patients on sunitinib) 2
• Elevated liver enzymes (AST/ALT increases occur in up to 39% of patients on sunitinib) 2
• Elevated lipase/amylase (occurs in up to 25% of patients on sunitinib) 2

Special Considerations

For High-Risk Patients

• More frequent monitoring may be needed for:
  • Patients with pre-existing liver disease
  • Elderly patients
  • Patients with comorbidities

For Specific Mutations

• PDGFRA exon 18 D842V mutation: These tumors are resistant to imatinib and may require alternative therapy (avapritinib) 1
• KIT exon 9 mutations: May require higher doses of imatinib (800mg) 1

Common Pitfalls to Avoid

1. Failing to perform molecular testing: Molecular analysis is essential for treatment planning as certain mutations predict response to specific TKIs 1

2. Inadequate monitoring of liver function: TKIs can cause hepatotoxicity, requiring regular monitoring of liver enzymes 2

3. Missing thyroid dysfunction: Hypothyroidism is common with sunitinib (occurs in up to 16% of patients) and requires regular TSH monitoring 2

4. Overlooking cardiac effects: Sunitinib can affect cardiac function and cause hypertension, necessitating cardiac monitoring 2

By following this comprehensive laboratory monitoring approach, clinicians can optimize treatment efficacy while minimizing toxicity for patients with GISTs.