“Ask Dr. HKSH” – Gastrointestinal Stromal Tumour

Dr. TONG King Hung, Daniel

Specialist in General Surgery

Q1. What is a gastrointestinal stromal tumour (GIST)?

A gastrointestinal stromal tumour (GIST) grows in the muscle layer of the digestive tract, not on the surface mucosa. Unlike oesophageal cancer or gastric cancer, which typically originates in the mucosal layer, a GIST arises from the muscle tissue beneath the mucosa. It is often discovered during endoscopy or imaging studies as a submucosal mass, and does not grow from the mucosa itself. How does GIST differ from typical colorectal or gastric cancer? Colorectal and gastric cancers have clear definitions: they are either malignant or benign. However, the definition of GISTs is less clear, and the malignancy is determined by factors such as tumour size, cell division rate, and whether they have spread or not.

Internationally, GISTs are classified into "very low risk," "low risk," "intermediate risk," and "high risk" based on specific scoring systems. Their behaviour also differs from typical gastric or colorectal cancers. While colorectal and gastric cancers often spread to lymph nodes, GISTs do not typically spread to the lymphatic system. If they metastasize, they spread directly to other organs.

Q2. How common is GIST in Hong Kong? What are the causes?

According to statistics, GISTs account for approximately 1% of all intestinal tumours in Hong Kong each year. The incidence may be underestimated as those small, slightly protruding masses found during endoscopy, which being benign and stable over time, are often GISTs. These benign tumours may go unnoticed until they grow larger and require treatment. The actual prevalence is likely higher than 1%.

Most GISTs have no clear or unknown causes. Research suggests that the most common factor is gene mutations. Mutations in certain genes may lead to uncontrolled tumour cell growth. The link of GISTs and other factors, such as diet or radiation, remains unproven.

Q3. How do doctors diagnose and stage GIST?

Doctors will first ask about symptoms and then arrange appropriate tests for diagnosis. GISTs are often asymptomatic, or only cause unrelated symptoms such as a slight stinging pain. They may already be malignant once they have grown very large and caused abdominal bloating, or even have become palpable. Early diagnosis is often possible with body checkups, such as endoscopy (gastroscopy or colonoscopy) or imaging studies such as CT scans, which can reveal a mass in an organ.

Patients often ask, “There’s a lump—could it be a tumour?” They want to know if it is serious and in what stage. Unlike typical gastrointestinal cancers, which are categorised as Stage 1, 2, 3, or 4 / or early, intermediate, and late, a different classification applies to GISTs. Staging depends on three factors: (1) tumour size, (2) whether it has spread or not, and (3) the cell division rate observed under a microscope after surgical removal. Tumours larger than 2 cm have a 10% chance of being malignant. Those larger than 5 cm are more likely to spread or recur after surgery, and the risk is even higher if they are over 10 cm. Thus, 2 cm, 5 cm, and 10 cm are used as key thresholds.

The second factor is if the tumour has spread or not. For example, if a tumour is found in both the gastrointestinal tract and liver, it is classified as metastatic. Patients often ask, “How is a tumour confirmed as a GIST upon discovery? Do I need a biopsy?” It has to do with treatment strategy:  if the tumour is small and can be completely removed by surgery, it should be excised and analysed to determine the cell division rate. However, whether the GIST is benign or has grown large (malignant), it is generally not recommended to perform a needle biopsy before surgery. Biopsies are only advised if the tumour has already spread and become inoperable, and requires pharmacological treatment.

Q4. How is GIST treated?

The general principle is that surgery is preferred if the tumour can be surgically removed. Thanks to advances in endoscopic techniques, minimally invasive surgery can now remove small tumours by lifting the mucosal layer and excising them endoscopically, e.g. through gastroscopy. For larger tumours deemed unsuitable for endoscopic removal, minimally invasive methods such as laparoscopy may be performed. However, if the tumour exceeds 10 cm, or even 20 to 40 cm in size, open surgery is often required. In short, surgical removal is the mainstay of treatment whenever feasible. If preoperative assessment indicates that complete removal is not possible, a tissue sample is taken to make sure that it is a GIST, not a rhabdomyosarcoma, lipoma, or other tumour. Targeted therapy may then be considered to achieve tumour shrinkage, followed by reassessment to determine the feasibility of curative removal.

Q5. Is surgery suitable for all patients?

Under certain circumstances, surgery is not suitable for some patients for two reasons. First, the patient’s physical condition may be poor. For example, if patients are in their 80s or 90s and need dialysis, rely on a pacemaker, or have heart failure, they may not tolerate anaesthesia. Secondly, the tumour’s condition may make surgery inappropriate. For instance, if one has a primary tumour in the oesophagus, stomach, or intestines, and also GISTs in the liver, lungs, bones, or other abdominal areas, surgery is not recommended as it would not be curative.

Q6. What treatment options are available if surgery is not suitable?

A tissue sample should first be taken to confirm a GIST diagnosis, followed by genetic analysis to identify the gene mutation in question and choose an appropriate targeted therapy. Many people think that the condition is hopeless if curative surgery is not suitable, but this is a special case. Targeted therapy works by focusing on specific receptors. A response rate of nearly 60 to 70% means, even if the tumour has spread, since it is caused by a gene mutation, targeted drugs can be highly effective for, or even cure specific GISTs. As condition varies from patient to patient, careful analysis is required to determine the treatment course.

Q7. Do targeted drugs have side effects? Will they affect the patient’s quality of life?

Many patients worry about targeted therapy, and ask if it involves intravenous injections, causes side effects such as hair loss, extreme fatigue, nausea, or health deterioration, or even prevents them from work.  These fears often stem from misconceptions about chemotherapy, while targeted therapy for GISTs does not necessarily cause these issues. The most common side effects are mild nausea and fatigue—only a slight tiredness, not debilitating exhaustion. Another side effect is swelling in the eyes, face, or body, which may indicate an allergic reaction to the drugs. Most patients can tolerate treatment well as long as if they are not allergic to the drugs. As the medications are taken orally like regular pills or vitamins without the need for intravenous administration, most patients can maintain a normal quality of life. Other options are available if one is allergic to the drugs. There are first-line and second-line targeted therapies, and multiple drugs are available. If a patient is allergic to one drug, there is always another option. While the effectiveness of first- and second-line drugs may differ, patients still have choices.

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