Surgery in Gastrointestinal Stromal Tumors (GISTs) for Treatment, Tumor Modeling, and Genomic Analysis

Objective: To follow people with GISTs and collect tumor tissue so that it can be studied in the lab. Eligibility: People age 6 and older who have a GIST. Design: Participants will be screened with a review of their medical records and samples. Participants will enroll in 1 other NIH study, and may be asked to enroll in 2 other optional NIH studies. Participants will have a medical history and physical exam. Data about how they function in their daily activities will be obtained. Participants may speak with a genetic counselor. They may have genetic testing. Participants will give blood samples. They may have a cheek swab. For this, small brush will be rubbed against the inside of the cheek. Participants may have a computed tomography (CT) scan of the chest, abdomen, and pelvis. Or they may have a CT scan of the chest and magnetic resonance imaging (MRI) of the abdomen and pelvis. Participants will be monitored every 6-12 months at the NIH Clinical Center, for up to 10 years before having surgery. If they need surgery, it will be performed at the NIH. Then, they will be monitored every 6-12 months, for up to 5 years after surgery. If a participant has surgery, tumor tissue samples and research specimen will be taken. If a participant does not need surgery, their participation will end after 10 years. If they have surgery, the 5-year monitoring period will restart after each surgery. ...

* INCLUSION CRITERIA: * Histological confirmation or clinical presentation suspicious of GIST; histological confirmation will be preferably by review of archival tissue if available, fresh biopsy will not be required if inadequate tissue sample. * Age \>= 6 years * ECOG performance status \= 60%) * Ability of participant or parent/guardian to understand and the willingness to sign a written informed consent document. EXCLUSION CRITERIA: \- Non-modifiable medical comorbidities that would preclude cytoreductive surgery.