Influence of an Acidic Beverage on the Imatinib Exposure After Major Gastrectomy

Inclusion Criteria: * Male or female patients ≥ 18 years of age * Patients with GIST, who previously underwent major gastrectomy * Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0-1 * Already selected to receive imatinib therapy in a dose of 400-800mg imatinib daily, as judged by the treating physician and with respect for and in agreement with the registration guidelines * Subject is able and willing to sign the Informed Consent Form prior to screening Exclusion Criteria: * Concomitant administration of any anti-cancer therapies (e.g. chemo-therapy, other targeted therapy, experimental drug, etc) other than imatinib * Concomitant use of medication which strongly inhibits or induces CYP3A4 * Refractory nausea and vomiting, malabsorption with other causes than gastrectomy or external biliary shunt that would preclude adequate absorption. * Unwillingness to use Coca-Cola * Unwillingness or inability to swallow whole tablets * Inability to comply with the requirements of the protocol * Inability to understand the nature and extent of the study and the procedures required * Participation in a drug study within 60 days prior to the first day of this study