Most GISTs arise sporadically as a consequence of somatic oncogenic mutations acquired during a person's lifetime, most commonly in the KIT gene encoding the KIT receptor tyrosine kinase. Mutations in succinate dehydrogenase subunit genes SDHB and SDHC characterize a distinct SDH-deficient GIST subtype that differs biologically, affects younger patients, and predominantly involves the stomach. Familial GIST syndrome, a rare hereditary form, follows autosomal dominant inheritance and results from germline mutations predisposing individuals to develop multiple GISTs over the course of their lifetime. The wild-type GIST subgroup, defined by absence of KIT, PDGFRA, and SDH gene mutations, represents a heterogeneous category with diverse alternative molecular drivers. Mutational subtype has direct clinical significance because different mutations confer differential sensitivity to available tyrosine kinase inhibitor therapies.

Tissue biopsy with histopathological examination is required for definitive diagnosis. GISTs characteristically express CD117 (KIT protein) by immunohistochemistry, which serves as a key diagnostic marker. DOG1 (anoctamin-1) and CD34 expression are also commonly assessed in the immunohistochemical panel. Molecular testing to identify specific mutations in KIT, SDHB, and SDHC is performed routinely, as the mutation subtype guides treatment selection. Cross-sectional imaging with computed tomography or magnetic resonance imaging is used for initial staging, treatment response monitoring, and surveillance. Endoscopic ultrasound provides detailed characterization of submucosal lesions accessible to endoscopy. Risk stratification combining tumor size, mitotic rate, and anatomic location is applied following resection to guide subsequent management decisions.

Surgical resection with negative margins is the primary approach for localized, resectable disease. For advanced, unresectable, or metastatic GIST, imatinib mesylate (Gleevec), a tyrosine kinase inhibitor approved by the FDA in 2003, is the foundational systemic therapy. Sunitinib malate (Sutent), approved in 2006, is used in patients with imatinib-refractory or imatinib-intolerant disease. Avapritinib (Ayvakit), approved in 2020, addresses GISTs harboring specific kinase domain mutations, including the PDGFRA Exon 18 D842V variant that does not respond to imatinib. Ripretinib is approved as a later-line option for patients who have received prior kinase inhibitor therapy. SDH-deficient GISTs, which typically lack actionable KIT or PDGFRA mutations, do not respond to standard imatinib therapy and require individualized management approaches.

Prognosis varies substantially according to established risk stratification criteria. Localized, small GISTs with low mitotic rates carry a favorable prognosis following complete surgical resection. Larger tumors and those with elevated mitotic rates at presentation carry higher risk of recurrence or distant metastasis. The introduction of targeted kinase inhibitor therapy has substantially extended survival in advanced and metastatic disease compared to the pre-imatinib era, when no effective systemic therapy existed. Resistance to successive kinase inhibitors remains a clinical challenge in advanced disease. SDH-deficient GISTs may follow a more indolent course despite propensity for lymph node spread and extended natural history distinguishing them from KIT-mutant GISTs. Familial GIST syndrome-associated tumors are managed with heightened long-term surveillance given germline predisposition.

Numerous active clinical trials are investigating GISTs across multiple disease settings, spanning early-phase dose-escalation studies to later-phase registration trials. Areas of active investigation include next-generation tyrosine kinase inhibitors designed to overcome resistance mutations that emerge with sequential inhibitor use, circulating tumor DNA-based biomarker strategies for detecting resistance mechanisms, and combination immunotherapy approaches. Studies specifically targeting wild-type and SDH-deficient GIST subtypes represent an area of dedicated research interest. ClinicalTrials.gov lists a large portfolio of enrolling studies for this condition.