Preoperative Imatinib Mesylate Combined With Rectal-sparing Surgery in Patients With c-KIT Gene-mutant Rectal GIST

Inclusion Criteria: 1. Over the age of 18. 2. Newly pathology-diagnosed rectal GIST 3. Tumor \> 2cm; local resection of R0 is not possible in the initial evaluation. 4. The lower margin of the tumor is ≤ 5cm from the anal verge. 5. C-KIT gene mutation. 6. Male or non-pregnant female. 7. ECOG score 0-2. 8. Did not receive targeted therapy before the start of the clinical trial. 9. Sufficient organ functions are defined as follows: Total bilirubin \< 1.5×ULN (upper limit of normal, ULN), serum AST (SGOT) and ALT (SGPT) \< 2. 5 × ULN, creatinine \< 1.5×ULN, neutrophil count \> 1. 5 ×109 / L, platelet \> 100 × 109 / L. 10. The patient's informed consent has been obtained. Exclusion Criteria: 1. Pathology is non-rectal GIST. 2. Under the age of 18. 3. Patients with distant metastasis. 4. The patient is not permitted to have additional primary malignant tumors within five years unless those tumors are currently deemed clinically insignificant and do not necessitate active intervention, such as basal cell skin cancer or cervical cancer in situ. The presence of any other malignant diseases is strictly prohibited. 5. Individuals diagnosed with stage III or IV cardiac conditions, specifically congestive heart failure and myocardial infarction occurring within six months prior to the commencement of the study. 6. The patient presents with severe and/or uncontrolled medical ailments, such as unmanaged diabetes, advanced chronic kidney disease, or active uncontrolled infection. 7. Co-administration of imatinib with warfarin or acetaminophen is contraindicated, necessitating the substitution of alternative medications (e.g., low molecular weight heparin in place of warfarin). 8. Subjects undergoing radiotherapy, chemotherapy, and/or targeted therapy. 9. Pregnant or lactating female patients. 10. Cognitive or psychiatric disorders. 11. Profound cardiac, hepatic, and renal dysfunction. 12. Non-adherence by the patient or the researchers' assessment of the patient's inability to complete the entire trial.