Elliot K. Fishman M.D.
Johns Hopkins Hospital

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“Mesenchymal tumors arise from mesenchymal cells in the gastric wall and include gastrointestinal stromal tumors (GISTs), non-GIST sarcomas, lipomas, lipomatosis, leiomyomas, schwannomas, and glomus tumors. GISTs are the most common subtype of mesenchymal tumors and can be either benign or aggressive. A well-circumscribed gastric mass with its epicenter in the submucosa and absence of perigastric lymphadenopathy favors a benign GIST diagnosis.”
Multimodality Imaging of Gastric Pathologic Conditions: A Primer for Radiologists
Anderson AC et al.
RadioGraphics 2020; 40:707–708

“All patterns of enhancement on contrast enhanced computed tomography (CECT) can be seen with GISTs, including hypoenhancing, isoenhancing, and hyperenhancing tumors. They can be large or small, endoluminal or exophytic. Clinical presentations include asymptomatic patients, nonspecific symptoms, obstruction, and bleeding. Bleeding can take the form of slow, intraluminal GI bleeding or massive intraperitoneal bleeding secondary to rupture and can be seen regardless of the enhancement pattern.” 
Getting the GIST: a pictorial review of the various patterns of presentation of gastrointestinal stromal tumors on imaging.
Scola D et al.
Abdom Radiol 2017 May;42(5):1350-1364. 

“The vast majority of GISTs are sporadic. Although rare, they can present in association with genetic syndromes including neurofibromatosis 1; Carney-Stratakis Syndrome, characterized by gastric GIST and paraganglioma; Carney Triad Syndrome which consists of (i) gastric GIST, (ii) pulmonary chondroma, and (iii) paraganglioma; and familial GIST syndrome.” 
Getting the GIST: a pictorial review of the various patterns of presentation of gastrointestinal stromal tumors on imaging.
Scola D et al.
Abdom Radiol 2017 May;42(5):1350-1364. 

“GISTs are the most common form of sarcoma, and as such no GIST can truly be classified as benign. Most patients have localized disease (79.4%), but approximately 11.4% have regional/distant metastatic disease at the time of presentation. Recurrences have been reported up to 30 years after initial diagnosis and resection. Metastasis during initial presentation or after resection more commonly involve the liver and peritoneal surfaces due to GISTs tendency for local invasion.” 
Getting the GIST: a pictorial review of the various patterns of presentation of gastrointestinal stromal tumors on imaging.
Scola D et al.
Abdom Radiol 2017 May;42(5):1350-1364. 

“Clinical presentations are highly variable and usually dependent on tumor size and location. Exophytic lesions are often large at the time of presentation, while smaller lesions that erode through the mucosa and result in mucosal ulceration can present earlier with GI bleeding. The most common symptoms are usually nonspecific, including abdominal pain, nausea, weight loss, or obstruction. Occasionally, patients may present with GI bleeding, which may be occult or take the form of frank hemorrhage with hemodynamic instability. Likewise, tumors can rupture on the external surface, causing intraperitoneal hemorrhage which can be life threatening.” 
Getting the GIST: a pictorial review of the various patterns of presentation of gastrointestinal stromal tumors on imaging.
Scola D et al.
Abdom Radiol 2017 May;42(5):1350-1364. 

All GIST 2 cm or larger in size are typically resected; the management of incidentally encountered GIST smaller than 2 cm in size remains controversial. There is no evidence that patients should undergo re-excision in cases in which there is complete resection of all macroscopic disease but microscopically margins are positive; watchful waiting and adjuvant imatinib may be appropriate for these patients. In general, gastric GIST 5 cm or smaller in size may be removed by laparoscopic wedge resection. Because GIST rarely involve the locoregional lymph nodes, extensive lymph node resection or resection is rarely indicated. These tumors may have fragile pseudocapsules, so care must be taken to avoid rupturing the pseudocapsule during surgery, which could result in peritoneal dissemination.

Before the advent of molecularly targeted therapy with TKI, efforts to treat GIST with conventional cytotoxic chemotherapy were essentially futile The extreme resistance of GIST to chemotherapy may be caused, in part, by the increased expression of P-glycoprotein, the product of the MDR-1 gene, and MRP1, which are cellular efflux pumps that may prevent chemotherapeutic agents from reaching therapeutic intracellular concentrations in GIST cells. There is universal agreement that standard chemotherapy has no role in the primary therapy of GIST.