Epidemiol/Biology
What is the mean age of presentation?
GIST is usually a disease of adults, with a median presenting age of 60 years and a slight male predominance.
What is the first imaging study of choice?
What are some cons?
CT AP with IV/PO contrast. GISTs appear as an enhancing mass arising in wall of stomach/small bowel. Can be seen as endophytic, exophytic, or intramural. Large masses may exhibit heterogenous enhancement resulting from fat necrosis.
Cons: Small GISTs may not be visible on CT, and some large hyper-vascular tumors may appear as primary liver tumors.
Name the therapy of choice and its mechanism of action.
Imatinib. It is a Tyrosine-kinase inhibitor.
What are the indications for resection?
>2cm, lack of prohibits comorbidities to surgery, and life expectancy of more than a few years. Smaller tumors may be followed with serial EGDs/imaging.
What cell type to GISTs arise from?
What are the most common locations of a GIST?
Intersticial cells of Cajal, an intestinal pacemaker cell found in the circular muscle.
Stomach: 40-60%
Small Bowel: 25-35% (rare in duodenum)
What are other imaging studies and what are they useful for?
MRI: To determine primary site if CT non-reliable or for small masses not readily seen on CT.
FDG-PET: If suspecting metastatic disease.
Who gets adjuvant therapy? Who doesn't?
Everyone with a KIT mutation.
Low risk tumors (<3cm and <5mitoses/HPF)
What are the margins of resection?
1cm, this ensures an R0 resection.
What are the most common presenting symptoms?
Non-specific: bloating, early satiety, abdominal pain, bleeding (if eroding into mucosa) or peritonitis (if perforation occurs).
What can you see on EGD?
Submucosal mass; may see ulceration due to erosion of mucosa or nothing if mass showing exophytic growth. Useful for biopsies.
What is the standard length of therapy?
3 years.
When resecting a GIST tumor in the lesser curvature, what structure are you worried about and what procedure can you do?
The vagus nerve.
Can do a pyloromyotomy.
What are poor prognostic factors?
>5cm, mitosis >5/HPF, non-gastric sites.
What is the role of FNA?
Helps differentiate a GIST from other tumors such as lymphomas, leiomyoma, adenocarcinomas. Most useful in cases requiring morbid operations (GEJ, periampullary). If non-diagnostic, repeat until conclusive if findings would lead to neoadjuvant use of Imatinib.
Who gets neoadjuvant therapy?
Locally advanced tumors requiring multi visceral resection, metastatic disease, large tumors, or tumors in difficult areas. This allows for down staging and organ preservation.
What are the complications of tumor rupture?
What can you do to help avoid this?
Intraperitoneal seeding. GISTs are very friable, more so if neoadjuvant therapy is given.
Do not handle the tumor itself but adjacent structures. Use a bag for specimen retrieval if laparoscopic.
How does a pediatric GIST differ from adults?
Often associated with SDH deficiency.
Female predominance.
Multifocal.
Frequent LN metastasis.
Universal Imatinib resistance.
What will you see on immunohistochemistry?
Spindle-shaped cells that stain positive for CD117.
What do you do if patient resistant to 1st line therapy?
Try second and third line TKI's such as Sunitinib or Regorafenib. Patients will typically respond to these agents.
During surgery, if failure to visualize stomach, what are some techniques to help you find it?
Stomach: If posterior, gastric mobilization. If intramural/intraluminal, can use intraoperative EGD or US.
In duodenum: Extensive Kocher maneuver and possible mobilization of LoT.
In jejunal/ileal tumors: Run the bowel from LoT to TI.