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Staging is a way of describing where the tumor is located, if or where it has spread, and whether it is affecting the functions of other organs in the body. Doctors use diagnostic tests to determine the tumor's stage, so staging may not be complete until all the tests are finished. Knowing the stage helps the doctor to decide what kind of treatment is best and can help predict a patient's prognosis (chance of recovery). There are different stage descriptions for different types of cancers.
One tool that doctors use to describe the stage of other types of cancer is the TNM system. This system judges three factors: the tumor itself (T), the lymph nodes (N) around the tumor, and if the tumor has spread to other parts of the body (metastasis, M). The results are combined to determine the stage of cancer for each person.
However, the use of the TNM system for GIST is not considered standard practice. Instead, doctors look at different factors to help determine a patient’s prognosis and the specific risk of how aggressive an individual tumor will be. Specifically, they want to determine how quickly it may grow and the likelihood of the tumor recurring (coming back) after surgery. Doctors use the factors listed below to determine how aggressive a tumor will be:
- The size of the tumor
- The mitotic count (the actual number of dividing cells)
The location where the tumor started.