Molecular basis for treatment of gastrointestinal stromal tumours

Twin pregnancy complicated by an adnexal mass

Gastrointestinal stromal tumours are mesenchymal neoplasms of the gastrointestinal tract.¹ This case study reports the incidental finding of a left sided adnexal mass in a woman with twin pregnancy. The presence of any mass during pregnancy raises issues for patient management, the effect on the developing fetus and mode of delivery.

Sorafenib inhibits many kinase mutations associated with drug-resistant gastrointestinal stromal tumors

Sorafenib has substantial clinical activity as third- or fourth-line treatment of imatinib- and sunitinib-resistant gastrointestinal stromal tumors (GIST). Because sorafenib targets both angiogenesis-related kinases (VEGFR) and the pathogenetic kinases found in GIST (KIT or PDGFRA), the molecular basis for sorafenib efficacy in this setting remains unknown. We sought to determine the spectrum of activity of sorafenib against different mutant kinases associated with drug-sensitive and drug-resistant GIST. We compared the activity of imatinib and sorafenib against transiently expressed mutant forms of KIT and PDGFRA, including various secondary mutations that have been identified in imatinib-resistant or sunitinib-resistant GISTs. We also examined these drugs against four GIST cell lines, three of which are imatinib resistant. In our in vitro studies, we determined that sorafenib inhibited imatinib-resistant mutations in exons encoding the ATP/drug-binding pocket and in exons encoding the activation loop, with the exception of substitutions at KIT codon D816 and PDGFRA codon 842. Notably our data indicate that sorafenib is more effective than imatinib or sunitinib for inhibiting the kinase activity of drug-resistant KIT mutants (as assessed by biochemical IC(50)). We hypothesize that a major determinant of the efficacy of sorafenib for treatment of advanced GIST is the activity of this agent against KIT or PDGFRA-mutant kinases. These results have implications for the further development of treatments for drug-resistant GIST.

Interstitial cells of Cajal do not harbor c-kit or PDGFRA gene mutations in patients with sporadic gastrointestinal stromal tumors

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are believed to originate from the interstitial cells of Cajal (ICCs) or from the precursors of ICCs. Most GISTs show an activating mutation in either the c-kit or platelet-derived growth factor receptor alpha (PDGFRA) gene that results in a constitutive, ligand-independent activation of receptor tyrosine kinases. These gene mutations may play an important role in transforming a GIST progenitor cell into a tumor cell during the early phase of GIST tumorigenesis. However, the precise mechanism of the tumorigenesis is not known.

METHODS

We examined ten patients with sporadic GIST for mutations in the tumor and its adjacent ICC cells, and compared the mutational status of ICC cells with that of the GIST cells in each patient. All cases were screened for mutations in the c-kit gene (exons 9, 11, 13, and 17) and in the PDGFRA gene (exons 12 and 18). Samples were limited to GIST cases from the small intestine, where ICCs were present in bundles and were considered suitable for isolation by laser capture microdissection.

RESULTS

Of the ten tumors screened, eight had mutations in the c-kit gene (all in exon 11) and two were wild-type, whereas none of the ICCs exhibited mutations in these genes.

CONCLUSIONS

Our results suggest that ICCs adjacent to overt GISTs did not have mutations in the c-kit or PDGFRA genes, and overt GISTs may develop after the local and sporadic acquisition of these gene mutations, together with additional events.

Consensus approaches to best practice management of gastrointestinal stromal tumors

Gastrointestinal stromal tumors are rare mesenchymal tumors of the gastrointestinal tract. Progress in diagnosis has led to increased recognition of this disease, and the availability of effective, molecularly targeted therapy has revolutionised its management. Treatment of metastatic gastrointestinal stromal tumors with imatinib has led to unprecedented improvements in progression free and overall survival and there are ongoing investigations into the optimal pre‐operative and adjuvant use of imatinib. Second‐line sunitinib is now available for patients who develop resistance to imatinib, and third‐ and fourth‐line therapies are being investigated in clinical trials. In this ever‐changing environment, evidence from controlled clinical trials and the authors' experience were used to comprehensively outline current best practice management of patients with gastrointestinal stromal tumors.