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Gastrointestinal stromal tumors (GIST): a rare entity, a tumor model for personalized therapy, and yet ten different molecular subtypes.

Gastrointestinal stromal tumors (GIST) are the most frequent sarcoma and were recognized as distinct molecular entities in 1998. Following the identification of driving molecular alterations in KIT, imatinib was rapidly introduced for the treatment of GIST, and became the paradigm of molecularly targeted therapies for solid tumors. While surgery was the only known effective treatment in 1998, two drugs are approved by the FDA and EMA in 2012 for the treatment of localized and advanced forms of this disease. Imatinib has been shown to provide a high level of clinical efficacy in patients with advanced GIST, a median progression-free survival (PFS) of 2 years and median overall survival close to 5 years, with 20% patients progression-free after 10 years of treatment. Imatinib has also been proven to improve overall survival and reduce the risk of relapse in localized GIST at high risk for relapse after resection. Sunitinib is indicated in advanced GIST after failure of imatinib, and provided a median PFS close to 6 months after imatinib failure. However, there is an important variability in the molecular and genetic characteristics that drive the pathogenesis of GIST, allowing thus for the identification of distinct molecular subtypes of GIST with different prognosis and sensitivity to the targeted treatments. Different strategies are now recommended in these different molecular subtypes of GIST which must be recognized as different entities regarding sensitivity to tyrosine kinase inhibitors and treatment decisions. This fragmentation of a yet recently recognized disease entity illustrates to strong trend of fragmentation in nosology of cancers, even in rare tumors such as GIST. For this aspect also, GIST is again a paradigmatic model for oncology, as many tumors with a higher prevalence will be fragmented in different molecular subsets and are going to become rare disease in the years to come.