GISTs are most common mesenchymal tumors of the gut but they account for less than one percent of all gastrointestinal tumors. GIST is a tumor of the special cells present in the wall of the gastrointestinal tract. These cells are called Interstitial cells of Cajal. These cells regulate the function and movements of the gut and are sometimes also called the pacemaker of gut.
Epidemiologically, GISTs are rare tumors. Only about 5000 new cases of GISTs are diagnosed every year in United States. Most of the tumors are smaller than four centimers in diameter, and are asymptomatic when they are diagnosed. A lot of the cases are discovered incidentally during radiological and endoscopic studies for any other GI tract abnormality. GISTs range from small benign tumors to metastatic malignant cancers.
GISTs: Clinical Presentation
Most GIST cases present during old age. The incidence of GISTs is almost equal in both genders. These tumors usually form a mass inside the gut which is responsible for most of the signs and symptoms. The clinical presentation of these tumors is as follows:
- A vague and nonspecific discomfort or pain in the abdomen is the most common symptom of GISTs
- Early satiety, which means a sensation of fullness after eating a small quantity of food
- Rarely, a GIST can be felt as a mass inside the abdomen. This mass is usually palpable on examination
- These tumors may bleed inside the gut. This may manifest as fatigue, malaise and shortness of breath
- In rare cases, a tumor may perforate the wall of the gut which results in the leakage of gut contents inside the abdominal cavity, leading to peritonitis
Gastrointestinal stromal tumors can also cause obstruction of the gut depending on their growth pattern. A tumor that is growing towards the lumen of the gut is more likely to block the gut. The symptoms of gut obstruction depend on the site of obstruction:
- A tumor in the esophagus may cause difficulty in swallowing, which is also called dysphagia
- A GIST in the colon or rectum may cause constipation
- A tumor in the duodenum may block the passage of bile and cause obstructive jaundice
The symptoms of GISTs vary in each patient depending on the size and site of the tumor. The diameter of gastrointestinal stromal tumors varies from one centimeter to as large as 40 centimeters. The most common location of these tumors is the stomach, which accounts for 60 to 70 percent of all cases. The small intestine is the second most common site of occurrence (20 to 30 percent). It is less common in the rest of the gastrointestinal tract.
GISTs are clinically and histologically diverse tumors. Some of them are indolent and slow-growing benign tumors while others are aggressive malignant carcinomas. For the same reason staging and grading is very important while making a diagnosis. The stage and grade of these tumors affect the clinical behaviour, treatment outcome and survival rates.
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The survival rate is also variable in these cases. It depends on the stage of the tumor at the time of diagnosis and whether the tumor is benign or cancerous. Benign tumors have a very high survival rate. As with many other tumors, early detection results in a very high survival rate. Since this tumor has vague and nonspecific symptoms, they are usually diagnosed when they have grown to a very large size. The five year survival rate after diagnosis ranges from 38 to 60 percent.
How Is A GIST Diagnosed And Managed?
GISTs are rare tumors and therefore the doctor usually rules out a number of other conditions that may cause the same symptoms before exploring the possibility that the patient has a GIST.
Diagnosising GIST
A GIST is diagnosed after a number of tests are done to rule out more common conditions. When there is no specific finding in these tests, a biopsy is done, which confirms the diagnosis.
The following laboratory tests are performed to rule out other causes of non-specific abdominal symptoms:
- Complete blood profile (CBC)
- Coagulation profile
- Renal Function tests (BUN and creatinine)
- Liver function tests
- Serum albumin
These imaging studies are performed to find the site and nature of abdominal pathology:
- Plain abdominal radiographs
- Barium studies
- Abdominal ultrasound
- CT scan abdomen and pelvis
- MRI of the abdomen
- PET scan
After these tests are completed, a mass or a lesion may be found somewhere in the GI tract but we can’t know what it is just by looking at the scans. So, in order to establish a definitive diagnosis, an endoscopic biopsy is carried out. The doctor goes inside your GI tract with a camera and light source and then the lesion is located. A piece of the lesion is taken out and sent to the laboratory for histopathological analysis. If the specific tumor cells of GISTs are detected, the diagnosis is confirmed.
Management Of Gastrointestinal Stromal Tumors
The exact management depends on the extent of the lesion. Patients with very small tumors that do not cause any symptoms are carefully monitored and no significant intervention is needed.
Surgery provides the definitive cure in most cases, especially if the tumor is localized and resectable. The tumor is resected along with some of the surrounding normal tissue. Surgery is usually indicated in cases of GIST, but if the disease is locally advanced, surgery becomes mandatory.
Laparoscopic surgery has been introduced recently. During a laparascopic operation, the tumor is resected with a very small incision. The surgery is performed through a telescope (a camera and light source). This procedure has also proven successful in the removal of gastrointestinal stromal tumors.
After the surgery the patient may be given some medication to decrease the chances of recurrence. It is called adjuvant therapy. Imatinib is the drug which is mostly used for this purpose. This drug may also be given before the surgery in order to shrink the tumor.
Medication is the only option for some cases. When the tumor is not resectable or the tumor has metastasized to other organs through the blood, surgery may be useless. In these cases, the patient is usually given Imatinib. This drug has proven effective in a lot of cases. If the patient does not respond to Imatinib, another drug called Sunitinib, may be given instead.
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Follow-up is very important after surgery. Regular clinical examination and periodic CT scans should be scheduled in accordance with the doctor's advice. Follow-up is really necessary to assess the recurrence of the disease.
Sources & Links
- Photo courtesy of Dan4th via Flickr: www.flickr.com/photos/dan4th/2284007457
- Photo courtesy of Dan4th via Flickr: www.flickr.com/photos/dan4th/2284007457
- Photo courtesy of timsamoff via Flickr: www.flickr.com/photos/timsamoff/69370701