What are GISTs?
What is this uncommon but important tumour called GIST?
GISTs, or gastrointestinal stromal tumours, are uncommon tumours that originate from the digestive system. However, they are different from the more frequent types of digestive tract cancers or adenocarcinomas, as they are specifically derived from unique cells called the interstitial cells of Cajal. These cells control the movement of food through the stomach and intestines, rather than the absorption, and are also known as the ‘pacemakers’ of the digestive system. GISTs are most commonly located at the stomach, but can also affect any part of the digestive system, including the small and large intestines, and the rectum.
GISTs had previously been among the most chemoresistant sarcomas, the arrival of imatinib (Glivec or Gleevec) and other tyrosine kinase inhibitor (TKI) drugs has transformed this cancer into a poster child for success in targeted treatment of cancer, with a very favourable side effect profile.
Symptoms of GIST
Many patients may not have any symptoms until they are in the advanced stages. The common symptoms of GIST include:
Blood in the stools or vomit
Symptoms of anaemia (low red blood count), including effort intolerance, giddiness, breathlessness
Are GISTs cancerous? How is it treated?
GISTs can be benign or cancerous. The larger the GIST, the more likely it is cancerous. However, even a small and seemingly benign GIST can behave like malignant cancer. Gastrointestinal stromal tumours can spread to other parts of the body, most commonly to the peritoneum and liver. The only certain way to determine whether GISTs are benign or cancerous is to remove them with surgery. Doctors then examine the tumour to determine the risk of relapse. High risk features for relapse or recurrence are:
High mitotic count/number of cells actively dividing and growing
Presence of rupture/spillage
A positive surgical margin
For patients with high risk for relapse, their chances of cure can be increased by taking 3 years of Imatinib (Glivec). This is an oral form of targeted therapy, and specifically targets GIST, sparing normal cells.
After 6 months of Glivec
If the tumour is too large to be removed, they can still be considered for surgery if it responds well to Glivec. For patients whose tumours have spread extensively and are not amenable to surgery, GISTs can be treated for prolonged periods with Glivec. Should resistance to Glivec eventually emerge, other approved therapies including increasing the dose of Glivec, or switching to other forms of targeted therapy, such as Sunitinib (Sutent) or Regorafenib (Stivarga). Other forms of treatment such as chemotherapy and radiotherapy are currently ineffective for treating GISTs.
Dr Thomas Soh
MRCP (United Kingdom)