Prospective multicentric randomized phase III study of imatinib in patients with advanced gastrointestinal stromal tumors comparing interruption versus continuation of treatment beyond 1 year: the French Sarcoma Group

Imatinib mesilate for the treatment of gastrointestinal stromal tumour

BACKGROUND

The molecular hallmark of gastrointestinal stromal tumours (GISTs), the mutation of the KIT gene, was discovered 10 years ago. GISTs have since been recognized as separate pathological entities among sarcomas, and have become a model for targeted treatment of solid tumours. Imatinib mesilate, which was approved in 2002 for the treatment of patients with advanced GIST, has dramatically changed the course of the disease.

OBJECTIVE

This article will focus on the development of imatinib mesilate in the treatment of patients with GIST.

METHODS

A Pubmed search was performed using the keywords 'imatinib', 'gastrointestinal stromal', 'GIST', 'KIT' and 'PDGFR'. Websites of the American Society of Clinical Oncology and the European Society of Medical Oncology were searched for data reported in abstract form at recent symposiums. Personal communications from opinion leaders were sought for additional information that might be relevant.

RESULTS

Imatinib has changed the clinical course of patients with advanced GISTs and further development in the adjuvant setting as well as prospective assessment of predictive factors are the current focus of ongoing research.

Drug Insight: gastrointestinal stromal tumors (GIST)--the solid tumor model for cancer-specific treatment

We are living in an exciting era in the treatment of cancer, using drugs that target specific proteins rather than agents that cause more general cytotoxic effects. The identification of proteins and signal transduction pathways that play crucial roles in the pathogenesis of cancer has allowed treatments to be designed that target these tumor-driven events. Gastrointestinal stromal tumors (GIST) are rare mesenchymal tumors and were among the first solid tumor types for which such a novel treatment (in this case imatinib) became available. The tyrosine kinase inhibitor imatinib targets the human KIT receptor and the platelet-derived growth factor receptor-alpha. This drug exhibits impressive antitumor effects against GIST and has become the first-line therapy for advanced disease. Major insights into the mechanism of action of this drug, drug resistance, and patient management issues have been gleaned. Additionally, new drugs developed for the treatment of GIST have been identified. As a consequence, lessons learned from GIST are widely applicable to other tumor entities, thereby rendering GIST the paradigm of solid tumors treated with tyrosine kinase inhibitors. This Review discusses the pathogenesis of GIST, treatment strategies, mechanisms accounting for drug resistance, and potential future perspectives.

3'-deoxy-3'-[18F]fluorothymidine positron emission tomography is a sensitive method for imaging the response of BRAF-dependent tumors to MEK inhibition

Activating mutations of BRAF occur in approximately 7% of all human tumors and in the majority of melanomas. These tumors are very sensitive to pharmacologic inhibition of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK), which causes loss of D-cyclin expression, hypophosphorylation of Rb, and G(1) arrest. Growth arrest is followed by differentiation or senescence and, in a subset of BRAF mutant tumors, by apoptosis. The former effects result in so-called "stable disease" and, in patients with cancer, can be difficult to distinguish from indolent tumor growth. The profound G(1) arrest induced by MEK inhibition in BRAF mutant tumors is associated with a marked decline in thymidine uptake and is therefore potentially detectable in vivo by noninvasive 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) positron emission tomography (PET) imaging. In SKMEL-28 tumor xenografts, MEK inhibition completely inhibited tumor growth and induced differentiation with only modest tumor regression. MEK inhibition also resulted in a rapid decline in the [(18)F]FLT signal in V600E BRAF mutant SKMEL-28 xenografts but not in BRAF wild-type BT-474 xenografts. The data suggest that [(18)F]FLT PET can effectively image induction of G(1) arrest by MEK inhibitors in mutant BRAF tumors and may be a useful noninvasive method for assessing the early biological response to this class of drugs.

Sunitinib in the management of gastrointestinal stromal tumours (GISTs)

AIMS

Gastrointestinal stromal tumours (GISTs) are rare mesenchymal neoplasms of the gut with a 5-year survival of approximately 50%. Surgery remains the treatment of choice in resectable disease, with conventional chemotherapy largely ineffective. Over 90% of GIST possesses mutations in the c-KIT oncogene, producing an overactive tyrosine kinase, which may be driving the malignant process. Imatinib inhibits the aberrant tyrosine kinase and imatinib therapy in metastatic disease has shown significant clinical benefit. However, resistance typically develops within 2 years, with the need for further therapy. This article aims to introduce the reader to a new development in cancer therapeutics.

METHODS

A literature search was performed using the MEDLINE database to identify publications relevant to the review. References within these articles were used to expand the search. Abstracts from recent ASCO symposia were hand searched for relevant articles.

FINDINGS

Sunitinib (SU11248) is a novel multi-targeted tyrosine kinase inhibitor with activity not only against the receptor tyrosine kinase product of c-KIT but also other cell-signalling pathways that may be relevant in GIST; FLT3, platelet-derived growth receptor (PDGFR) and vascular endothelial growth factor receptor (VEGFR). Two Phase II trials and one Phase III trial have investigated the activity of sunitinib against imatinib-resistant GIST. Early results showed significant benefits in time to disease progression that led to licensing of the drug in America and more recently in Europe. A Phase III trial comparing dose-increased imatinib and sunitinib in progressed GIST is currently planned.

CONCLUSIONS

Initial clinical results with sunitinib are promising and suggest a future role. Further studies are needed before sunitinib can be recommended for the routine treatment of imatinib-refractory GIST.

The challenge of opportunities: how far can and should we go with targeted treatments and modern diagnostics in gastrointestinal stromal tumors?

The introduction of imatinib has greatly improved the treatment options and quality of life of patients with gastrointestinal stromal tumors. Systemic treatment with imatinib alone most likely, however, does not cure the disease because, despite long-lasting major remissions, the majority of patients eventually relapse. Therefore, complete surgical resection remains the only curative approach in patients with gastrointestinal stromal tumors. Given a strong systemic treatment option at hand, the use of multimodal treatment strategies for patients with locally advanced or metastatic disease seems self-evident as many tumors become resectable after a treatment with imatinib. Few retrospective and no prospective data, however, are yet available on feasibility and the prognostic impact of these strategies, which represents a major challenge on how to decide on these patients in clinical practice. We therefore critically discuss the available evidence and current concepts for multimodal treatment of gastrointestinal stromal tumors and how modern diagnostics, such as KIT genotyping, may influence our clinical decision-making in this context.