Imatinib Mesylate in Treating Patients With Primary Gastrointestinal Stromal Tumor That Has Been Completely Removed By Surgery

Inclusion Criteria:

* Patient must have an ECOG/Zubrod performance status of =\< 2
* Patient must have a histologic diagnosis of primary GIST (without peritoneal or distant metastasis) that expresses Kit protein by immunohistochemistry and have tumor size \>= 3cm in maximum dimension
* Patient must have undergone complete gross resection (includes R0 \[negative microscopic margins\] and R1 \[positive microscopic margins\]) of a primary GIST within 70 days prior to registration
* Patient must have a chest x-ray completed within 28 days prior to registration; NOTE: Chest CT within 28 days prior to registration can be used in lieu of chest x-ray
* 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
* Platelets \>= 100,000/mm\^3
* Total Bilirubin =\< 1.5 times the institution ULN; NOTE: Patients with elevated bilirubin secondary to Gilbert's disease are eligible to participate in the study
* AST =\< 2.5 times the institution ULN
* ALT =\< 2.5 times the institution ULN
* Female of childbearing potential must have negative serum pregnancy test; NOTE: Post-menopausal women must be amenorrheic for at least 12 months to be deemed not of reproductive potential
* 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
* Patient must provide written authorization to allow the use and disclosure of their protected health information; NOTE: This may be obtained in either the study-specific informed consent or in a separate authorization form and must be obtained from the patient prior to study registration (non-US sites are exempt from HIPAA regulations)
* If patient is a cancer survivor, ALL of the following criteria 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 postoperative CT scan or MRI of the abdomen or pelvis
* Patient, if female and breastfeeding; NOTE: It is not known whether STI571or its metabolites are excreted in human milk; however, in lactating female rats administered 100mg/kg, a dose approximately equal to the maximum clinical dose of 800mg/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; 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 (1mg orally per day) for prevention of central line-associated deep venous thrombosis is permitted