Dedifferentiated Gastrointestinal Stromal Tumor

**Semantic type:** Neoplastic Process

**Definition:** A gastrointestinal stromal tumor that through the process of dedifferentiation, results in an uncommon phenotype. Dedifferentiation in the context of GIST, may manifest as loss of CD117 expression and regression from specialized tissue to a more anaplastic/pleomorphic appearance, high nuclear atypia, high mitotic activity, and necrosis.