Inclusion Criteria:

- Patient must have an ECOG/Zubrod performance status of ≤ 2

- Patient must have a diagnosis of high-risk primary GIST; NOTE: High risk is defined
as tumor size ≥ 10 cm in maximum dimension, or the presence of tumor rupture before
or during surgery, intraperitoneal hemorrhage or multifocal (< 5) intraperitoneal
tumors

- Patient must have undergone complete gross resection (includes R0 [negative
microscopic margins] and R1 [positive microscopic margins] resections) of a primary
GIST within 70 days prior to registration

- Patient must have a histologic diagnosis of GIST that is confirmed by central
pathology review

- Patient's tumor must stain positive for the Kit receptor tyrosine kinase on
immunohistochemistry as determined by the central pathologist using the Dako (Dako
Corp., Carpinteria, CA) anti-CD 117 antibody

- Patient must have a chest x-ray completed within 28 days prior to registration

- Patient must have a post-operative CT scan with IV and PO contrast or MRI with
contrast (if allergic to CT contrast) of abdomen and pelvis within 28 days prior to
registration

- Creatinine ≤ 1.5 times the institution ULN

- WBC ≥ 2,000/mm^3

- Platelet ≥ 100,000/mm^3

- Total bilirubin ≤ 1.5 times the institution ULN

- AST and ALT ≤ 2.5 times the institution ULN

- Female of childbearing potential must have negative serum pregnancy test

- Patient or the patient's legally acceptable representative must provide a signed and
dated written informed consent prior to registration and any study related procedures

- If patient is a cancer survivor, each of the following criteria must apply:

- Patient has undergone potentially curative therapy for all prior malignancies,

- No evidence of any prior malignancies for at least 5 years with no evidence of
recurrence (except for effectively treated basal cell or squamous carcinoma of
the skin, carcinoma in-situ of the cervix that has been effectively treated by
surgery alone, or lobular carcinoma in-situ of the ipsilateral or contralateral
breast treated by surgery alone)

- Patient is deemed by their treating physician to be at low risk for recurrence
from prior malignancies

Exclusion Criteria:

- Patient has received post-operative chemotherapy

- Patient has received post-operative radiation therapy

- Patient has received post-operative investigational treatment

- Patient has received prior therapy with STI571

- Patient has had an active infection requiring antibiotics within 14 days prior to
registration

- Patient has objective evidence of residual disease on the post-operative CT scan or
MRI of the abdomen or pelvis

- Patient, if female and breastfeeding; NOTE: It is not known whether STI571 or its
metabolites are excreted in human milk; however, in lactating female rats
administered 100 mg/kg, a dose approximately equal to the maximum clinical dose of
800 mg/day based on body surface area, STI571 and/or its metabolites were extensively
excreted in milk; it is estimated that approximately 1.5% of a maternal dose is
excreted into milk, which is equivalent to a dose to the infant of 30% the maternal
dose per unit body weight; because many drugs are excreted in human milk and because
of the potential for serious adverse reactions in nursing infants, women should be
advised against breastfeeding while taking STI571

- Patient has New York Heart Association class 3 or 4 cardiac disease

- Patient is taking full dose warfarin; NOTE: The use of mini-dose warfarin (1 mg
orally per day) for prevention of central line-associated deep venous thrombosis is
permitted