Some Lessons Learned from Imatinib Mesylate Clinical Development in Gastrointestinal Stromal Tumors

Imatinib mesylate is a molecular-targeted agent, shown to be effective in chronic myeloid leukemia and gastrointestinal stromal tumors (GIST). The latter may currently serve as a model on which speculating how the future of molecular-targeted therapy in solid tumors will be. So far, some lessons have been learnt. 1) Molecular-targeted therapy can be effective in the advanced disease setting, resulting in major tumor responses. 2) Patterns of tumor responses may be peculiar, radiologically and pathologically. 3) Anti-tumor activity may be highly predictable by assessing tumor molecular biology. 4) The methodology of clinical development of molecular-targeted agents may differ from standard chemotherapy in some respects, because, say, the preclinical rationale may be stronger, thus increasing the Bayesian prior probability of efficacy, or the optimal dose cannot be determined separately from the assessment of activity and efficacy. 5) Molecular-targeted agents will hardly remain "orphan drugs", if effective. 6) While an obvious impact on survival in the advanced disease setting has been clearly demonstrated, the biologic and clinical impact of molecular-targeted therapy still needs to be elucidated. Its eradicating capabilities, as well as the implications of secondary resistance, are to be understood. 7) Integrated, multimodality approaches, including surgery, may still be of value in the molecular-targeted therapy era.

Imatinib and gastrointestinal stromal tumors: Where do we go from here?

Imatinib has tremendously changed the treatment of gastrointestinal stromal tumor (GIST). Research is currently focusing on its optimal use and the mechanisms of resistance that may emerge. A multidisciplinary approach including medical oncologists, surgeons, radiologists, and pathologists is crucial for the optimal management of these patients. Moreover, imatinib treatment in GIST represents an extraordinary model to expand our knowledge on the molecular mechanisms that are basic to the effects of molecularly targeted therapies. This review summarizes the existing knowledge of the imatinib treatment in GIST and describes directions for further development.