What is GIST?
GIST means Gastrointestinal Stromal Tumor; it is a rare tumor of the gastrointestinal tract. It occurs most commonly in the stomach (50–60 %); followed by the small intestine (30–35 %) and less frequently in the colon/rectum, esophagus, mesentery, omentum, and retroperitoneum. There are several different sub-types of cancer and GIST is in the sub-type called sarcoma.
What causes GIST?
- Most cases are sporadic (not inherited) and are caused by mutations in genes like KIT and PDGFRA. The reasons these mutations develop are not well understood.
- Some GISTs are known to be inherited (germline) due to mutations in genes like SDH and NF1 mutations.
(Mutation: A change in the sequence of nucleotides in a gene, often resulting in a change of the sequence of amino acids in a protein.)
How is the cancer staged?
Single tumor at diagnosis – About 80% of GIST patients have a single tumor at the time of diagnosis.
Metastatic disease at diagnosis – In about 20% of cases the cancer has spread from the original site to distant locations such as the liver and peritoneum. These distant tumors are called metastases.
Staging is decided according to the location, size of the tumor, and how fast the cancer is growing/multiplying (low or high) – accordingly it will be categorized as low, intermediate, or high risk of having a recurrence. If it has spread to other organs it is advanced/metastatic cancer.
Is gene mutation testing necessary?
- In non-metastatic disease (localized), mutation testing is done on surgical specimens. This helps doctors to understand how the cancer may behave and what type of treatment should be given, so that the patient may have less chance of disease recurrence.
- In metastatic disease, mutation testing is done to select therapy. For example, if the patient has a c-KIT mutation, imatinib is used; while for those with a PDGFRA exon 18 D842V mutation with metastatic disease, initial treatment should be with avapritinib rather than other TKIs as these patients are resistant to imatinib. Also, patients with SDH mutations respond poorly to imatinib.
Is it enough to visit any oncologist or it is necessary to see a specialist?
With the recent and considerable advances in the management of GIST, it is better to meet a GIST specialist who can guide the patient and advise on the tests to be taken, so that patients may have access to the best available treatment.
What is the main treatment involved?
Treatment is dependent on the stage of the disease.
Single tumor at diagnosis
Surgery is the main treatment. For low or intermediate-risk patients, surgery is often curative. Whereas, for high-risk patients with imatinib-sensitive mutations, adjuvant imatinib is typically given for 3 to 5 years. If the patient has a recurrence after adjuvant treatment is stopped, they are typically restarted on imatinib.
Metastatic disease at diagnosis
Imatinib is typically prescribed as most GISTs have imatinib-sensitive mutation types. However, mutational testing is important to identify non-imatinib-sensitive mutation types so that the patient can be directed to the best medication. About 8-10% of GISTs will have PDGFRA mutations and two-thirds of these will be a D842V mutation. This mutation does not respond to imatinib, sunitinib, or regorafenib. However, it does respond to avapritinib. Surgery may also play a part in the treatment plan.
What if imatinib does not work, or the patient becomes resistant?
If the disease progresses on imatinib treatment, other drugs like sunitinib, regorafenib, avapritinib, and ripretinib are available. The latter two drugs were recently approved in 2020 and are available under special support programs.
Are there any side effects of the drug?
Yes, common side effects are fatigue, nausea, body pain, and differences in blood count and platelet count. The doctor will be monitoring the patient for these side effects. Most patients tolerate the drug well and side effects improve over time.
Does chemotherapy work for treating GIST?
Research shows that traditional chemotherapy and radiation are not effective in the treatment of GIST.
What kind of monitoring is needed?
A CT Scan or PET Scan is recommended every 3-6 months by a doctor to monitor the response to treatment. If the disease is decreased/or remains the same size, the same therapy is continued. If it increases, your therapy may be changed.
Will insurance pay for the drugs?
Many drug companies offer financial help or discount programs. For insurance, please check the policy documents which have the details of what is covered under cancer treatment.
Do we have any support groups in India?
Yes, we have the Sachin Sarcoma Society (SSS) performing a wonderful job of connecting patients and doctors. Furthermore, The Life Rraft Group assists in connecting patients internationally and provides information and resources for the patient community.
What type of support do they give?
They connect patients to specific doctors, and they support them emotionally by sending positive messages.
What type of attitude should the patient have?
Be positive. Be Happy. Find solace with the family members and caregivers and face the thing with the attitude “Cancer is Conquerable”. With new available treatment options and better care, most patients do well.