Imatinib is a tyrosine kinase inhibitor that results in an inhibition of tumor growth. It may or may not be associated with a decrease in tumor size.
Initial resistance indicates disease progression within 3 months of starting imatinib therapy.
Risk factors for initial resistance:
(1) presence of lung metastases
(2) absence of liver metastases
(3) low hemoglobin (< 11.27 mg/dL, or < 7 mmol/L)
(4) high baseline absolute granulocyte count(> 5,000 per µL)
Late resistance indicates a lack of disease progression during the first 3 months of starting imatinib therapy, with progression occurring afterwards.
Risk factors for late resistance:
(1) high baseline absolute granulocyte count(> 5,000 per µL)
(2) primary tumor located outside of the stomach
(3) large tumor size (> 12 cm)
(4) low initial imatinib dose (400 mg per day, vs 400 mg bid)
Limitations:
• A metastatic GIST is malignant. The term "advanced" seems a bit ambiguous vis a vis the degree of malignancy of the tumor.
