Gastrointestinal stromal tumors (GIST) are a group of tumors that originate independently from the mesenchymal stem cells of the gastrointestinal tract; they are mesenchymal tumors of the gastrointestinal tract, proposed and named by Mazur and Clark, and are mostly positive for CD117 immunohistochemical staining. GIST depends on early detection and surgical resection, but 85% of patients will recur after surgery; inoperable patients and those with metastases are not sensitive to conventional radiotherapy and chemotherapy, with poor prognosis and 5-year survival rate less than 35%. Imatinib mesylate, a tyrosine kinase inhibitor, has revolutionized the treatment of GIST with its outstanding efficacy and good tumor control. Meanwhile, the further improvement in the understanding of GIST gene mutations has led to a significant increase in the diagnosis rate of GIST. Consensus on pathological diagnosis 1. Requirements for specimens: For post-surgical tissue specimens must be fixed in a timely manner, requiring complete immersion in sufficient (at least 3 times the volume of the specimen) 10% neutral formalin solution for fixation within 30 minutes of specimen isolation. For tumors ≥50px in diameter, they should be cut at 25px intervals during fixation; the fixation time should be 12-48 hours to ensure the feasibility and accuracy of subsequent immunohistochemical and molecular biological assays. Meanwhile, it is recommended to keep fresh tumor tissues for freezing for further genetic testing in the future. 2. Pathological diagnosis of GIST: The pathological diagnosis of GIST must be made based on the results of gross pathology, pathological histology and immunohistochemical testing together. Immunohistochemical staining for CD117 (95% positive rate), CD34 (70% positive rate), SMA (40% positive rate), S-100 (5% positive rate) and Desmin (2% positive rate) is very useful for the auxiliary diagnosis of GIST. The diagnosis of GIST can be made in cases with histology consistent with typical GIST and positive CD117, and positive CD117 expression should be localized to the tumor cell membrane and cytoplasm. About 5% of histomorphologically suspicious GISTs with negative immunohistochemical staining for CD117 are recommended for diagnosis by testing for DOG1 and/or Nestin, PDGFR; molecular biology is also needed to detect mutations in KIT and PDGFRA genes to aid in diagnosis. For difficult cases, pathologists need to consult and discuss to make the final diagnosis. 3. Treatment of CD117 negative cases: 1. Cases with histological manifestations consistent with typical GIST and CD117 negative: For tumors with histological manifestations consistent with typical GIST and CD117 negative, they should be referred to qualified molecular biology laboratories for detection of mutations in c-kit or PDGFRA genes to assist in diagnosis. The loci to be tested for mutations should include, at a minimum, exons 11, 9, 13 and 17 of the c-kit gene and exons 12 and 18 of the PDGFRA gene. Since most GIST (65%-85%) mutations occur in exon 11 or exon 9 of the c-kit gene, priority can be given to detecting these two exons. For the detection of the above six common exon mutations, the polymerase chain reaction (PCR) amplification-direct sequencing method is recommended. 2.Cases with histological manifestations consistent with typical GIST but CD117 negative and no gene mutation: For cases with histology consistent with typical GIST but CD117 negative and without the above gene mutation, other tumors (such as smooth muscle tumors, fibromatosis and neurogenic tumors, etc.) must be systematically excluded, after which the diagnosis of GIST can also be made. 4.Gene testing: Gene mutation testing helps to diagnose some difficult cases, predict the efficacy of targeted therapy drugs and guide clinical treatment. The expert group recommends mutation analysis in the following cases: all recurrent, metastatic and drug-resistant GISTs; primary resectable GISTs with intermediate to high risk biological behavior, and cases considered for adjuvant imatinib therapy; cases requiring mutation testing to confirm or exclude the diagnosis of GIST; identification of pediatric, familial and NF1-related GISTs. 5. Primary complete resection Risk assessment of GIST: The assessment of risk for limited GIST should be comprehensive and detailed, including: tumor size, nuclear split image, site of primary tumor and whether tumor rupture occurs. The previously applied NIH risk classification includes the size of the tumor and the number of nuclear divisions per 50 high-powered views (50 high-powered views where nuclear schizograms are abundant must be counted). Several retrospective studies have confirmed the significant correlation between these two indicators and the prognosis of GIST, and also found that relying on these two indicators alone to predict the prognosis of GIST patients is not sufficient. After long-term follow-up of 1684 GIST patients, Miettinen and Lasota et al. classified the risk level of GIST into 8 grades based on survival data. This new GIST risk grading scheme integrates tumor size, nuclear split images, and tumor site. Studies in large samples have demonstrated that GISTs originating in the small intestine have a worse prognosis than GISTs originating in the stomach. Because intra-abdominal contamination due to tumor rupture is a more valuable clinical prognostic indicator, detailed documentation of rupture, whether spontaneous or intraoperative, is required in the medical record. in April 2008, the National Institutes of Health (NIH) specifically organized experts to revisit the grading of risk after resection of primary GIST, and a consensus was reached (Table 1). In this new classification, the primary tumor site (GISTs originating outside the stomach have a poorer prognosis than those originating in the stomach) and tumor rupture are used as indicators for prognostic assessment.