Imatinib TDM in GIST

Inclusion Criteria:

• Histologically or cytologically confirmed GIST with KIT mutation or PDGFRA mutation (non-D842V)

• Currently receiving imatinib initiated within the last 3 months or to be started inthe next 1 month

• Prior systemic chemotherapy for other malignancy is allowed as long as it wascompleted within the past 6 months and there is no evidence of disease

• Age ≥18 years

• ECOG performance status of 0 or 1

• Normal organ function

Exclusion Criteria:

• Presence of PDGFRA D842V mutation

• Known allergy to imatinib or allergic reactions to compounds of similar chemical orbiologic composition to the study drug

• Concomitant anticoagulation with oral warfarin.

• Use of strong inhibitors or inducers of CYP3A or CYP3A4, drugs metabolized by CYP3A4or CYP2D6

• Uncontrolled intercurrent illness

• Concurrent malignancy