Systemic therapy for advanced gastrointestinal stromal tumors: beyond imatinib

Progression on first-line therapy with imatinib in gastrointestinal stromal tumors (GIST) is caused by either initial resistance or more often a secondary mutation in tyrosine kinases KIT or PDGFR. Therapies in development for imatinib-resistant GIST include agents that target KIT/PDGFR with greater potency or possess broader kinase inhibition profiles including VEGFR. To circumvent secondary mutations in KIT/PDGFR, inhibition of the downstream signaling in PI3K/Akt/mTOR pathway and enhanced degradation of KIT/PDGFR are also under investigation.

Clinical and molecular characteristics of gastrointestinal stromal tumors in the pediatric and young adult population

Gastrointestinal stromal tumors (GISTs) typically occur late in life; however, there also are reports of pediatric and young adult patients. This rare subset of GISTs has clinicopathologic and molecular features distinct from their adult counterparts. Most pediatric GIST patients are female and often present with multifocal tumors that are epithelioid in nature. Although these young patients often have metastatic disease, it progresses slowly. Most pediatric GISTs lack the gain-of-function mutation in KIT or PDGFRA commonly found in adult cases. Expression profiling and genomic studies of pediatric GISTs show distinct molecular signatures, suggesting a unique origin as compared with adult GISTs. We and others have shown that the insulin-like growth factor 1 receptor may have a prominent role in driving KIT/PDGFRA mutation-negative adult and pediatric GISTs, and clinical trials are currently being designed to exploit these types of discoveries.