Wen‐Bin Ou

PURPOSE: Gastrointestinal stromal tumors (GISTs) commonly harbor oncogenic mutations of the KIT or platelet-derived growth factor alpha (PDGFRA) kinases, which are targets for imatinib. In clinical studies, 75% to 90% of patients with advanced GISTs experience clinical benefit from imatinib. However, imatinib resistance is an increasing clinical problem. PATIENTS AND METHODS: One hundred forty-seven patients with advanced, unresectable GISTs were enrolled onto a randomized, phase II clinical study of imatinib. Specimens from pretreatment and/or imatinib-resistant tumors were analyzed to identify molecular correlates of imatinib resistance. Secondary kinase mutations of KIT or PDGFRA that were identified in imatinib-resistant GISTs were biochemically profiled for imatinib sensitivity. RESULTS: Molecular studies were performed using specimens from 10 patients with primary and 33 patients with secondary resistance. Imatinib-resistant tumors had levels of activated KIT that were similar to or greater than those typically found in untreated GISTs. Secondary kinase mutations were rare in GISTs with primary resistance but frequently found in GISTs with secondary resistance (10% v 67%; P = .002). Evidence for clonal evolution and/or polyclonal secondary kinase mutations was seen in three (18.8%) of 16 patients. Secondary kinase mutations were nonrandomly distributed and were associated with decreased imatinib sensitivity compared with typical KIT exon 11 mutations. Using RNAi technology, we demonstrated that imatinib-resistant GIST cells remain dependent on KIT kinase activity for activation of critical downstream signaling pathways. CONCLUSION: Different molecular mechanisms are responsible for primary and secondary imatinib resistance in GISTs. These findings have implications for future approaches to the growing problem of imatinib resistance in patients with advanced GISTs.

PURPOSE: Most gastrointestinal stromal tumors (GISTs) harbor mutant KIT or platelet-derived growth factor receptor alpha (PDGFRA) kinases, which are imatinib targets. Sunitinib, which targets KIT, PDGFRs, and several other kinases, has demonstrated efficacy in patients with GIST after they experience imatinib failure. We evaluated the impact of primary and secondary kinase genotype on sunitinib activity. PATIENTS AND METHODS: Tumor responses were assessed radiologically in a phase I/II trial of sunitinib in 97 patients with metastatic, imatinib-resistant/intolerant GIST. KIT/PDGFRA mutational status was determined for 78 patients by using tumor specimens obtained before and after prior imatinib therapy. Kinase mutants were biochemically profiled for sunitinib and imatinib sensitivity. RESULTS: Clinical benefit (partial response or stable disease for > or = 6 months) with sunitinib was observed for the three most common primary GIST genotypes: KIT exon 9 (58%), KIT exon 11 (34%), and wild-type KIT/PDGFRA (56%). Progression-free survival (PFS) was significantly longer for patients with primary KIT exon 9 mutations (P = .0005) or with a wild-type genotype (P = .0356) than for those with KIT exon 11 mutations. The same pattern was observed for overall survival (OS). PFS and OS were longer for patients with secondary KIT exon 13 or 14 mutations (which involve the KIT-adenosine triphosphate binding pocket) than for those with exon 17 or 18 mutations (which involve the KIT activation loop). Biochemical profiling studies confirmed the clinical results. CONCLUSION: The clinical activity of sunitinib after imatinib failure is significantly influenced by both primary and secondary mutations in the predominant pathogenic kinases, which has implications for optimization of the treatment of patients with GIST.

Endometrial stromal sarcoma (ESS) is a genetically heterogenous group of uterine sarcomas, of which almost half are associated with JAZF1 rearrangement. We recently identified a novel genetic fusion between YWHAE and FAM22A/B in ESS harboring t(10;17)(q22;p13) and herein describe the clinicopathologic features of 13 YWHAE-FAM22 ESS cases (11 primary and 3 metastatic) and compare them with 20 ESS cases with JAZF1 rearrangement. Ten of 11 primary uterine tumors contained morphologically high-grade areas composed of round cells arranged in nests with a delicate stromal capillary network. The tumor cells showed large nuclei with irregular nuclear contours and significant mitotic activity (>10 mitoses/10 HPF) in addition to focal tumor necrosis, in contrast to JAZF1 ESS, which lacked a nested growth pattern, were composed of cells with small round/oval nuclei, and typically had <5 MF/10 HPF. In 7 of the 11 uterine tumors, there was an additional cytologically bland and mitotically weakly active spindle cell component with a fibrous/fibromyxoid stroma (ESS, fibromyxoid variant). Two metastatic tumors (pulmonary) also contained round cell and spindle cell components, whereas 1 metastasis (vaginal) was composed solely of the spindle cell component. In both primary and metastatic tumors, the spindle cells were diffusely positive for estrogen and progesterone receptors and CD10, in contrast to the round cell areas, which were negative. Clinically, 10 of 12 patients with YWHAE-FAM22 ESS presented with FIGO stages II to III disease, in contrast to only 4 of 16 patients with JAZF1 ESS presenting with stages II to III disease (P<0.05). Tumors with YWHAE-FAM22 rearrangements constitute a distinct group of ESS, which is associated with high-grade morphology and aggressive clinical behavior compared to JAZF1 ESS. Thus, their distinction from typical JAZF1 ESS is important for prognostic and therapeutic purposes.

14-3-3 proteins are ubiquitously expressed regulators of various cellular functions, including proliferation, metabolism, and differentiation, and altered 14-3-3 expression is associated with development and progression of cancer. We report a transforming 14-3-3 oncoprotein, which we identified through conventional cytogenetics and whole-transcriptome sequencing analysis as a highly recurrent genetic mechanism in a clinically aggressive form of uterine sarcoma: high-grade endometrial stromal sarcoma (ESS). The 14-3-3 oncoprotein results from a t(10;17) genomic rearrangement, leading to fusion between 14-3-3ε (YWHAE) and either of two nearly identical FAM22 family members (FAM22A or FAM22B). Expression of YWHAE-FAM22 fusion oncoproteins was demonstrated by immunoblot in t(10;17)-bearing frozen tumor and cell line samples. YWHAE-FAM22 fusion gene knockdowns were performed with shRNAs and siRNAs targeting various FAM22A exons in an t(10;17)-bearing ESS cell line (ESS1): Fusion protein expression was inhibited, with corresponding reduction in cell growth and migration. YWHAE-FAM22 maintains a structurally and functionally intact 14-3-3ε (YWHAE) protein-binding domain, which is directed to the nucleus by a FAM22 nuclear localization sequence. In contrast to classic ESS, harboring JAZF1 genetic fusions, YWHAE-FAM22 ESS display high-grade histologic features, a distinct gene-expression profile, and a more aggressive clinical course. Fluorescence in situ hybridization analysis demonstrated absolute specificity of YWHAE-FAM22A/B genetic rearrangement for high-grade ESS, with no fusions detected in other uterine and nonuterine mesenchymal tumors (55 tumor types, n = 827). These discoveries reveal diagnostically and therapeutically relevant models for characterizing aberrant 14-3-3 oncogenic functions.

Abstract Renal Medullary Carcinoma (RMC) is an aggressive malignancy that affects young black individuals with sickle cell trait. No effective treatment is available, resulting in an ominous clinical course, with overall survival averaging less than four months. We report rearrangement of the ALK receptor tyrosine kinase in a pediatric case of RMC harboring a t(2;10)(p23;q22) translocation. Mass spectrometry‐based proteomic evaluation identified a novel ALK oncoprotein in which the cytoskeletal protein vinculin (VCL) was fused to the ALK kinase domain. The resulting VCL‐ALK fusion does not contain known self‐association domains, but includes the talin binding domains of vinculin. We demonstrate coprecipitation of strongly tyrosine phosphorylated talins with the VCL‐ALK oncoprotein, suggesting that ALK oncogenic crossphosphorylation is mediated by interactions between neighboring VCL‐ALK proteins on a talin scaffold. This report widens the spectrum of ALK‐related tumors and ALK fusion partners, and provides a rationale for treating RMC with targeted ALK inhibitors. © 2010 Wiley‐Liss, Inc.