There are a number of types of GIST. A little more than ten years ago, GIST was a disease that was frequently misdiagnosed – usually as leiomyosarcoma. Today, not only can we use immunohistochemistry to diagnosis GIST, but also to identify several subtypes. By adding mutational testing, these subtypes can further be broken down by gene mutation and exon.
Some of the types of GIST we know about are:
The most common type, it can occur anywhere in the GI tract and is most commonly diagnosed in older adults. Responses to medications can vary by mutation type (KIT, PDGFRA, “Wild Type”) and mutation location (exon 9, 11, etc.), and this forms additional subtypes of GIST. In particular, the PDGFRA D842V mutation is completely resistant to Gleevec and Sutent. Clinical trials are available for advanced GIST patients with the D842V mutation, both as first-line therapy and for patients that have had Gleevec or Sutent.
Rarer than adult GIST (approx. 5%-10% of all GIST patients), and with a different defective protein (succinate dehydrogenase, or SDH), it is slower growing than the adult form and most often starts in the stomach. More prevalent in females than males. Most people consider pediatric-like GIST to be a subtype of wildtype GIST. Pediatric-like GIST is also known as SDH-deficient GIST. Read more about pediatric-like GIST. . .
Found in approximately 15% of all GIST cases, this is the label given when the common mutations in KIT and PDGFRA are not found. At the current time, wildtype encompasses rare mutations, such as SDH, BRAF, NF1 and cases where the mutation is unknown. It is possible that the definition for wildtype GIST may change in the future with increased understanding of rare mutations. It’s becoming more important to identify the specific subtype of wildtype GIST, as optimal treatments may vary by subtype. Read more about wildtype GIST. . .
Familial or hereditary GIST
An inherited form of GIST. A small number of patients inherit the disease from one of their parents. While in other GISTs only some of the body’s cells are affected by the mutation, in familial GIST all of the cells are. The disease has a pediatric form as well. Read more. . .
Rare GISTs in which the primary tumor occurs outside of the GI tract. As these can be confused with other types of tumors besides GIST, it is important to confirm the diagnosis. Read more. . .