Gastrointestinal Stromal Tumor: Staging, Grading, Treatment

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TNM is the most commonly used system for staging GISTs by the medical community. “T” stands for “Tumor Size”, “N” for “Lymph Nodes”, and “M” for “Metastasis”. Numbers and/or letters after T (1, 2, 3, and 4), N (0 and 1), and M (0 and 1) provide more details about each of these factors.

Additionally, GIST is graded to assess the aggressiveness of the disease. The grading of GIST is based on the mitotic activity (the rate of cancerous cell division). The grade is assigned as Low or High, where Low grade means low rate of cell division.

Once T, N, and M categories and the grade of a tumor are determined, this information is combined to assign an overall stage (from 0 to IV) to the disease. Following table describes the characteristics of different stages of GIST of the stomach/omentum (a layer of fatty tissue covering the abdominal organs), small intestine, esophagus, colon, rectum, or peritoneum:

Gastrointestinal Stromal Tumor Staging:

STAGETNM and GRADEStomach/OmentumSmall Intestine/ Esophagus/ Colon/ Rectum/ Peritoneum
IAT1-2 N0 M0 LowThe primary tumor is </=5 cm in size. No spread to nearby lymph nodes or distant body parts. The assigned grade is Low.N/A
IBT3 N0 M0 LowThe primary tumor size is >5 cm but </=10 cm. No spread to nearby lymph nodes or distant body parts. The assigned grade is Low.N/A
IT1-2 N0 M0 LowN/AThe primary tumor is </=5 cm in size. No spread to nearby lymph nodes or distant body parts. The assigned grade is Low.
IIT3 N0 M0 LowN/AThe primary tumor size is >5 cm but </=10 cm. No spread to nearby lymph nodes or distant body parts. The assigned grade is Low.
T1-2 N0 M0 HighThe primary tumor is </=5 cm in size. No spread to nearby lymph nodes or distant body parts. The assigned grade is High.N/A
T4 N0 M0 LowThe primary tumor size is >10 cm. No spread to nearby lymph nodes or distant body parts. The assigned grade is Low.N/A
IIIAT1 N0 M0 HighN/AThe primary tumor is </=2 cm in size. No spread to nearby lymph nodes or distant body parts. The assigned grade is High.
T4 N0 M0 LowN/AThe primary tumor size is >10 cm. No spread to nearby lymph nodes or distant body parts. The assigned grade is Low.
T3 N0 M0 HighThe primary tumor is >5 cm but </=10 cm in size. No spread to nearby lymph nodes or distant body parts. The assigned grade is High.N/A
IIIBT4 N0 M0 HighThe primary tumor size is >10 cm. No spread to nearby lymph nodes or distant body parts. The assigned grade is High.N/A
T2-4 N0 M0 HighN/AThe primary tumor size may range from >2 cm to >10 cm. No spread to nearby lymph nodes or distant body parts. The assigned grade is High.
IVAny T N1 M0 Any GThe primary tumor of any size. The disease has spread to nearby lymph nodes. No spread to distant body parts. The assigned grade may have any value.The primary tumor of any size. The disease has spread to nearby lymph nodes. No spread to distant body parts. The assigned grade may have any value.
Any T Any N M1 Any GThe primary tumor of any size that might or might not have spread to nearby lymph nodes. The disease has spread to distant body parts, such as the liver. The assigned grade may have any value.The primary tumor of any size that might or might not have spread to nearby lymph nodes. The disease has spread to distant body parts, such as the liver. The assigned grade may have any value.

GIST treatment usually depends on many factors, including but not limited to stage of disease, the location of the disease, performance status of the patient, side effects associated with the treatment, patient’s preference, along with other factors.

Following is the preferred treatment approache for GIST, but the final decision is taken after clinical assessment of the patient by an oncologist.

Gastrointestinal Stromal Tumor Treatment

Tumor CharacteristicsTreatment
Localized, resectable tumorsFor small, resectable, low-grade tumors, surgical resection to remove all cancerous tissue is the preferred approach. Targeted drug (e.g. Imatinib) should be employed after surgical resection to prevent disease recurrence in case of intermediate or high risk disease.
Localized, marginally resectable tumorsFor localized GISTs that cannot be completely removed with surgery (marginally resectable tumors), targeted therapy should be considered as the first-line treatment. This should be continued until the cessation of clinical benefit. In case of a good response to treatment (sufficient shrinkage to resectable disease), surgical resection to remove all cancerous should be attempted. After surgery, a continuation of the targeted drug is generally recommended to prevent disease recurrence.
In case of the cessation of clinical benefit and unresectable disease, the dose of the targeted drug should be increased or a different drug may be employed.
Disseminated, unresectable tumorsFor disseminated GISTs that cannot be removed with surgery (unresectable tumors), targeted therapy should be considered as the first-line treatment. This should be continued until the cessation of clinical benefit. In case of a good response to treatment (sufficient shrinkage to resectable disease), surgical resection to remove all cancerous should be attempted.
In the case of the cessation of the clinical benefit and unresectable disease, the dose of the targeted drug should be increased or a different drug may be employed.

Following is the brief description of various treatment types employed for GIST:

  1. Surgery: Surgery is the treatment of choice for most early-stage and some higher stage GISTs that has not spread to distant body parts and can be completely removed. The goal of surgery is to remove entire cancerous tissue along with some healthy tissue. However, a complete resection is not always possible, such as in the case of advanced-stage disease, the disease involving a vital organ/structure, or when a surgical resection will lead to a significant functional disability. Surgery may also be performed to collect biopsy sample in some cases.

  2. Targeted Therapy: Targeted drugs works differently than chemotherapy drugs that they target a specific gene or protein characteristic of the cancer cells that help them to divide and grow indefinitely. In GIST, c-kit mutation may be targeted with the help of targeted therapies like Imatinib, Sunitinib or Regorafenib.

  3. Ablation and Embolization: These techniques are generally employed to treat GISTs that have spread to the lungs or liver. In ablation, small secondary tumors are destroyed without actual removal from the body. High-energy radio waves are utilized in radiofrequency ablation (RFA), microwaves are used in microwave ablation (MWA) technique, while very cold gases are used in cryoablation to destroy tumors. In embolization, small (relatively larger than ablation) secondary cancers are destroyed by blocking the blood supply to the cancer cells with the help of some inert tiny particles (particles are loaded with drugs in chemo-embolization and with a radioactive substance in radio-embolization) that are injected directly in the artery supplying blood to cancer cells. Embolization can sometimes be employed in conjunction with ablation. Imaging techniques are utilized along with these techniques to accurately locate the target tumors.

  4. Palliative Treatment: It do not directly treat GIST but helps in improving the overall quality of life by providing relief from the symptoms and by reducing the suffering caused by the disease. It is generally given as supportive care for advanced staged STSs along with other treatments. It may include but not limited to: using drugs or other interventions to reduce swelling, pain, bleeding, and other symptoms such as nausea, vomiting, and diarrhea; surgical interventions or radiotherapy may also be employed.

It is very important to assess the benefits of each treatment option versus the possible risks and side effects before making a treatment decision. Sometimes, patient’s choice and health condition are also important to make a treatment choice.

Following are the goals for GIST treatment:

  • Prolongation of life.
  • Reduction of symptoms.
  • Improvement of overall quality of life.

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