Two types of mesenchymal tumours arise in the gastrointestinal tract:
- The most common type are gastrointestinal stromal tumours, which are unique to the gastrointestinal tract
- Other mesenchymal tumours that occur elsewhere in the body (eg. leiomyoma, leiomyosarcoma) can also arise in the gastrointestinal tract but are much less frequent than GIST
The advent of immunohistochemistry and understanding of GIST has allowed easier classification of these tumours; as the modern definition was only developed in 1999 there are numerous reports of treatment for "GIST" that may not apply to the modern setting; conversely a number of mesenchymal tumours of the gastrointestinal tract were previously referred to as sarcomas were actually GIST.