Some tumors can be removed by surgery and pose little risk of coming back. This type of tumor is often referred to as a benign tumor. However, other tumors may have a higher risk of coming back. These tumors are commonly called malignant tumors. If a tumor returns after surgery, it is called a recurrence.
Most cancers arise from a single tumor at a single site in the body. This tumor is called a primary tumor. After surgery, a tumor can return at the same site (a local recurrence) or a new tumor can occur at a different site (metastasis). Metastases (commonly called “mets”) can be present at the time of diagnosis or they can appear sometime after surgery (a recurrence). They form when tumor cells detach from the primary tumor and travel through the circulatory system (blood, lymph) and attach in distant locations. These tumor cells then act as seeds for new tumors.
Gastrointestinal stromal tumors (GISTs), unlike other cancerous tumors, are not classified as benign or malignant. Rather, they are stratified on a risk scale of low to high risk based on tumor size, mitotic index and location of tumor. Mutation may also play a role in determining risk. The NCCN guidelines strongly recommend testing of tissue removed by biopsy or surgery for mutations in the KIT and PDGFRA genes or the SDH gene if no mutations were found in the KIT or PDGFRA. For more information on GIST Mutations and Mutation Testing.
Based on a consensus guideline formulated in 2001 on the diagnosis and morphologic prognostication of GISTs, many experts consider that all GISTs may have malignant potential (Zhao & Yue, 2012). Other experts consider gastric GISTs smaller than 2cm essentially benign, whereas the non-gastric ones tend to be have a higher risk of recurrence and malignant potential (NCCN guidelines, 2016).
Knowing your estimated risk of recurrence is especially important if you are considering adjuvant Gleevec (imatinib). Patients with a low risk or very low risk tumor may not need to take adjuvant Gleevec (imatinib). At least three years of adjuvant treatment is recommended for GIST patients with a high risk of recurrence. In the United States adjuvant Gleevec (imatinib) is also recommended for patients with intermediate risk, although the duration of treatment is not specified (NCCN, 2016). A recent study by Quek, et.al, 2016 has shed a light on this uncertainty by demonstrating how mutational analysis can improve risk stratification for this subgroup of patients who may benefit from adjuvant Gleevec (imatinib). In the study, intermediate risk GIST patients with KIT Exon 11 deletion mutations had inferior clinical outcomes, with recurrence-free survival comparable to high risk patients.
There are several different methods used to classify the risk of recurrence in GIST. Some have advantages over others for specific cases (for example, if the primary tumor site is unknown, one method has advantages over others). An understanding of how it is calculated should prove helpful in determining your prognosis and treatment plans with the help of your health care team.
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