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Jonathan A Fletcher

Publications and source records attributed to Jonathan A Fletcher.

At least 55 records · Page 3Linked to original sources
PubMed2003

PDGFRA activating mutations in gastrointestinal stromal tumors.

Most gastrointestinal stromal tumors (GISTs) have activating mutations in the KIT receptor tyrosine kinase, and most patients with GISTs respond well to Gleevec, which inhibits KIT kinase activity. Here we show that approximately 35% (14 of 40) of GISTs lacking KIT mutations have intragenic activation mutations in the related receptor tyrosine kinase, platelet-derived growth factor receptor alpha (PDGFRA). Tumors expressing KIT or PDGFRA oncoproteins were indistinguishable with respect to activation of downstream signaling intermediates and cytogenetic changes associated with tumor progression. Thus, KIT and PDGFRA mutations appear to be alternative and mutually exclusive oncogenic mechanisms in GISTs.

Animals↗
PubMed2003

Genetic and biological subgroups of low-stage follicular thyroid cancer.

Investigations of cancer-specific gene rearrangements have increased our understanding of human neoplasia and led to the use of the rearrangements in pathological diagnosis of blood cell and connective tissue malignancies. Here, we have investigated 3p25 rearrangements of the peroxisome proliferator-activated receptor gamma (PPAR gamma) gene in follicular epithelial tumors of the human thyroid gland. Eleven of 42 (26%) low-stage follicular carcinomas, 0 of 40 follicular adenomas, 1 of 30 Hurthle cell carcinomas, 1 of 90 papillary carcinomas, and 0 of 10 nodular goiters had 3p25 rearrangements by interphase fluorescence in situ hybridization. All 11 follicular carcinomas with 3p25 rearrangement exhibited strong, diffuse nuclear immunoreactivity for PPAR gamma, consistent with expression of PPAR gamma fusion protein. Twelve of 42 (29%) low-stage follicular carcinomas had 3p25 aneusomy without PPAR gamma rearrangement (P = 0.01), suggesting that PPAR gamma rearrangement and aneuploidy are independent early events in follicular cancer. Eleven of 12 follicular carcinomas with 3p25 aneusomy exhibited no PPAR gamma immunoreactivity, supporting the existence of two independent pathways. Follicular carcinoma patients with PPAR gamma rearrangement more frequently had vascular invasion (P = 0.01), areas of solid/nested tumor histology (P < 0.001), and previous non-thyroid cancers (P < 0.01) compared with follicular carcinoma patients without PPAR gamma rearrangement. Our experiments identify genetic subgroups of low-stage follicular thyroid cancer and provide evidence that follicular carcinomas with PPAR gamma rearrangement are a distinct biological entity. The findings support a model in which separate genetic alterations initiate distinct pathways of oncogenesis in thyroid carcinoma subtypes.

Adenocarcinoma, Follicular↗
PubMed2003

The role of chromosomal translocation (15;19) in the carcinoma of the upper aerodigestive tract in children.

OBJECTIVE: To further evaluate the role of chromosomal translocation (15;19) in the presentation of the carcinoma (CA) of the upper aerodigestive tract. STUDY DESIGN AND SETTING: A retrospective study at a tertiary care pediatric medical center. RESULTS: Seven patients with a mean age of 12 years presented with CA of nasopharynx (N = 2), sinonasal region (N = I), parotid gland (N = 2), or larynx (N = 2). Treatments included combinations of surgery (N = 5), chemotherapy (N = 5), and radiation therapy (N = 4). One patient with sinonasal CA and one patient with laryngeal CA had chromosomal translocation (15;19); these patients both died of their disease with a mean survival of 6 months. The 5 patients without translocation (15;19) responded well to treatment and are disease-free with a mean follow-up of 47 months. CONCLUSION: The preliminary results appear to indicate poor prognosis associated with the presentation of chromosomal translocation (15;19) despite aggressive multi-modality treatment. Further investigation is needed to better understand the cause and relationship of the translocation (15;19) and aggressive behavior of these tumors.

Adolescent↗
PubMed2003

Inhibition of FLT3 in MLL. Validation of a therapeutic target identified by gene expression based classification.

We recently found that MLL-rearranged acute lymphoblastic leukemias (MLL) have a unique gene expression profile including high level expression of the receptor tyrosine kinase FLT3. We hypothesized that FLT3 might be a therapeutic target in MLL and found that 5 of 30 MLLs contain mutations in the activation loop of FLT3 that result in constitutive activation. Three are a newly described deletion of I836 and the others are D835 mutations. The recently described FLT3 inhibitor PKC412 proved cytotoxic to Ba/F3 cells dependent upon activated FLT3 containing either mutation. PKC412 is also differentially cytotoxic to leukemia cells with MLL translocations and FLT3 that is activated by either overexpression of the wild-type receptor or mutation. Finally, we developed a mouse model of MLL and used bioluminescent imaging to determine that PKC412 is active against MLL in vivo.

Animals↗
PubMed2003

Detection by the fluorescence in situ hybridization technique of MYC translocations in paraffin-embedded lymphoma biopsy samples.

The detection of chromosomal translocations by fluorescence in situ hybridization (FISH) is widely performed, but very few studies have attempted to apply this technique to paraffin-embedded routine biopsy samples. We report the analysis of paraffin sections from 36 B-cell lymphoma biopsies for MYC translocation breakpoints by FISH. The probes consisted of multi-YAC constructs that flanked the breakpoint region and that, therefore, separate upon a chromosomal translocation and generate split (or "segregated") signals (rather than a more ambiguous "co-localization" pattern, obtained when the two partners in a hybrid gene are detected). The results were assessed by a simple approach that avoids the counting of signal numbers per nucleus and so is appropriate for use in routine practice. A total of 19 of the 36 lymphomas were scored as positive for MYC translocation and this included 16 of the 20 patients in whom classic cytogenetics had shown the presence of the (8;14) translocation (or one of its two variants). We conclude that this two-colour "split-signal" technique based on breakpoint flanking probes can readily detect chromosomal translocations in paraffin sections. Furthermore, our results suggest that cases categorized as "atypical Burkitt's/Burkitt-like" lymphoma (at least for adult patients) are heterogeneous with respect to translocations involving the MYC oncogene, as well as immunophenotype and clinical features.

Adolescent↗
PubMed2003

HER-2/neu testing in breast cancer.

The testing of newly diagnosed breast cancer specimens for HER-2/neu status has achieved "standard of practice" status for the management of breast cancer in the United States. The discussion as to the best method to determine HER-2/neu status in these samples continues, with the fluorescence in situ hybridization method gaining popularity owing to the recent evidence that it, in comparison with immunohistochemical analysis, might more accurately predict clinical responses to trastuzumab-based therapies. With trastuzumab achieving excellent results in the treatment of HER-2/neu-positive advanced disease and under extensive evaluation in major clinical trials for its potential efficacy when used at earlier clinical stages, the potential role(s) for HER-2/neu testing as a predictor of response to other therapies being resolved by large prospective clinical outcome studies, and the more convenient gene-based chromogenic in situ hybridization technique "waiting in the wings," the saga of HER-2/neu testing in breast cancer will continue to unfold over the next several years.

Antibodies, Monoclonal↗
PubMed2003

The Her-2/neu gene and protein in breast cancer 2003: biomarker and target of therapy.

The HER-2/neu oncogene encodes a transmembrane tyrosine kinase receptor with extensive homology to the epidermal growth factor receptor. In this review, the association of HER-2/neu gene and protein abnormalities with prognosis and response to therapy with trastuzumab and to other therapies in breast cancer is presented. By considering a series of 80 published studies encompassing more than 25,000 patients, the relative advantages and disadvantages of Southern blotting, polymerase chain reaction amplification, and fluorescence in situ hybridization assays designed to detect HER-2/neu gene amplification are compared with HER-2/neu protein overexpression assays performed by immunohistochemical techniques applied to frozen and paraffin-embedded tissues and enzyme immunoassays performed on tumor cytosols. The significance of HER-2/neu overexpression in ductal carcinoma in situ and the HER-2/neu status in uncommon female breast conditions and male breast cancer are also considered. The role of HER-2/neu testing for the prediction of response to trastuzumab therapy in breast cancer is presented as well as its potential impact on responses to standard and newer hormonal therapies, cytotoxic chemotherapy, and radiation. The review also evaluates the status of serum-based testing for circulating HER-2/neu receptor protein and its ability to predict disease outcome and therapy response.

Adult↗
PubMed2003

Gonadotropic pituitary carcinoma: HER-2/neu expression and gene amplification. Report of two cases.

The authors report on two gonadotropic carcinomas of the adenohypophysis that occurred in a55-year-old man (Case 1) and a 53-year-old woman (Case 2), with signs of mass effect and amenorrhea, respectively. Both lesions were macroadenomas. The tumor in Case 1 metastasized to dura mater, skull, nasal sinus, and larynx 2 years after patient presentation, whereas that in Case 2 spread to vertebral bodies and ribs after a 19-year latency. Histologically, the primary, recurrent, and metastatic lesions in Case 1 featured brisk mitotic activity and high MIB-1 levels as well as p53 labeling indices. Immunoreactivity for HER-2/neu was assessable only in rare neoplastic cells of the second recurrence and in 80% of cells of the dural metastasis. Low-level HER-2/neu gene amplification was evident in the recurrent tumors and metastasis. The sellar and metastatic tumors in Case 2 resembled benign gonadotropic adenoma with oncocytic change; p53 accumulation, HER-2/neu overexpression, and HER-2/neu gene amplification were not present. The results indicate that low-level amplification of the HER-2/neu gene might be associated with pituitary carcinomas in which more aggressive behavior is seen. Further studies are needed to determine whether HER-2/neu plays a role in the pathogenesis of pituitary carcinoma.

Brain Neoplasms↗
PubMed2003

Soft tissue sarcomas of adults: state of the translational science.

Sarcomas--like leukemias, which are also mesodermal malignancies--carry biological significance disproportionate to their clinical frequency. Identification of mutations and translocations associated with these tumors has illuminated aberrant signaling pathways that cause these diseases, determine their behavior, and are therapeutic targets. Activated receptor-associated tyrosine kinase c-kit, mutated in most gastrointestinal stromal tumors, has proven a clinically effective target for enzyme inhibition. A translocation involving a single gene family, consisting of EWS and related genes, has been identified in five different sarcomas, and its chimeric protein products could prove similarly amenable to inhibitors. Resolution of the histopathological complexity is being aided by data from molecular and chromosomal characterization. Improvements in imaging, definition of prognostic factors, and surgical and radiotherapeutic treatment have resulted in improved local control. Continued progress will depend on further adapting the rapidly evolving technologies of genomics and proteomics. It will also depend upon accurate histopathological diagnosis based on validated reagents and consistent methodologies applied to adequate tissue samples derived from patients with complete clinical data. Finally, multicenter, coordinated trials, such as those that occurred with assessment of imatinib mesylate in metastatic gastrointestinal stromal tumors, will assure the most rapid reductions in morbidity and mortality.

Adult↗
PubMed2002

Constitutive activation of insulin receptor substrate 1 is a frequent event in human tumors: therapeutic implications.

Insulin receptor substrate 1 (IRS-1) is a major substrate of insulin, insulin-like growth factors, and cytokine signaling and plays an important role in mediating apoptosis, cell differentiation, and cell transformation. We found that IRS-1 is constitutively activated in a variety of solid tumors, including breast cancers, leiomyomas, Wilms' tumors, rhabdomyosarcomas, liposarcomas, leiomyosarcomas, and adrenal cortical carcinomas. Blocking the constitutively activated IRS-1 signaling in breast cancer cells with a dominant-negative IRS-1, an IRS-1 with all 18 potential tyrosine-phosphorylation sites replaced by phenylalanines (F18), dramatically reduced cancer cell growth. Breast cancer cells that expressed F18 also formed smaller and far fewer colonies in soft agar culture than did the cells that did not express F18. These studies suggest that constitutive IRS-1 activation is a common phenomenon in tumors and that activated IRS-1 may present an attractive therapeutic target.

Breast Neoplasms↗
PubMed2002

Prognostic value of KIT mutation type, mitotic activity, and histologic subtype in gastrointestinal stromal tumors.

PURPOSE: Previous studies have reported clinical correlates for KIT mutations in GISTs, but in most of those studies the KIT mutations were found in less than 50% of the GISTs. The aim of this study was to evaluate the prognostic relevance for KIT mutations in a series of GISTs in which the mutations were evaluated intensively by genomic and cDNA sequencing. PATIENTS AND METHODS: A comprehensive clinical and pathologic analysis of 48 patients with GISTs who had snap-frozen tissue was performed. The median tumor size was 10 cm (range, 2 to 30 cm). Median follow-up for disease-free patients was 48 months. KIT genomic and cDNA was sequenced by using nucleic acid templates isolated from frozen tumors. RESULTS: The overall 5-year recurrence-free survival was 41% +/- 6%. Five-year recurrence-free survival for patients with tumors that had mitotic counts of three mitoses or fewer per 30 high-power fields (HPF), more than three to <or= 15 mitoses per 30 HPF, and more than 15 mitoses per 30 HPF were 89% +/- 7%, 49% +/- 12%, and 16% +/- 6%, respectively (P =.0001). The 32 patients with spindle-cell histology had a 49% +/- 7% 5-year recurrence-free survival; in contrast, the 16 patients with epithelioid or mixed histology had a 23% +/- 11% 5-year recurrence-free survival (P =.01). Five-year recurrence-free survival for patients with tumors less than 5 cm, 5 to 10 cm, and more than 10 cm were 82% +/- 12%, 45% +/- 9%, and 27% +/- 8%, respectively (P =.03). Prognostic associations were found with particular KIT mutation types, and patients with missense exon 11 mutations had a 5-year recurrence-free survival of 89% +/- 11% compared with 40% +/- 8% for GISTs with other mutation types (P =.03). The independent predictors for disease-free survival were the presence of deletion/insertion exon 11 mutations (hazard ratio [HR] = 4; P =.006), more than 15 mitoses per 30 HPF (HR = 18; P =.0001), mixed histology (HR = 21; P =.0001), and male sex (HR = 3; P =.05). CONCLUSION: In this series of KIT-expressing GISTs, tumor mitotic activity and histologic subtype were the most important prognostic features. The majority of GISTs contain KIT-activating mutations with the type/location of mutation serving as an independent predictor for disease-free survival. These results suggest that KIT mutation and activation are important in GIST pathogenesis and also may provide important prognostic information.

Adult↗
PubMed2002

Efficacy and safety of imatinib mesylate in advanced gastrointestinal stromal tumors.

BACKGROUND: Constitutive activation of KIT receptor tyrosine kinase is critical in the pathogenesis of gastrointestinal stromal tumors. Imatinib mesylate, a selective tyrosine kinase inhibitor, has been shown in preclinical models and preliminary clinical studies to have activity against such tumors. METHODS: We conducted an open-label, randomized, multicenter trial to evaluate the activity of imatinib in patients with advanced gastrointestinal stromal tumor. We assessed antitumor response and the safety and tolerability of the drug. Pharmacokinetics were assessed in a subgroup of patients. RESULTS: A total of 147 patients were randomly assigned to receive 400 mg or 600 mg of imatinib daily. Overall, 79 patients (53.7 percent) had a partial response, 41 patients (27.9 percent) had stable disease, and for technical reasons, response could not be evaluated in 7 patients (4.8 percent). No patient had a complete response to the treatment. The median duration of response had not been reached after a median follow-up of 24 weeks after the onset of response. Early resistance to imatinib was noted in 20 patients (13.6 percent). Therapy was well tolerated, although mild-to-moderate edema, diarrhea, and fatigue were common. Gastrointestinal or intraabdominal hemorrhage occurred in approximately 5 percent of patients. There were no significant differences in toxic effects or response between the two doses. Imatinib was well absorbed, with pharmacokinetics similar to those reported in patients with chronic myeloid leukemia. CONCLUSIONS: Imatinib induced a sustained objective response in more than half of patients with an advanced unresectable or metastatic gastrointestinal stromal tumor. Inhibition of the KIT signal-transduction pathway is a promising treatment for advanced gastrointestinal stromal tumors, which resist conventional chemotherapy.

Adolescent↗
PubMed2002

Molecular genetic characterization of the EWS/CHN and RBP56/CHN fusion genes in extraskeletal myxoid chondrosarcoma.

Extraskeletal myxoid chondrosarcoma (EMC) is a soft-tissue neoplasm cytogenetically characterized by the translocations t(9;22)(q22;q11-12) or t(9;17)(q22;q11), generating EWS/CHN or RBP56/CHN fusion genes, respectively. In the present study, 18 EMCs were studied both cytogenetically and at the molecular level. Chromosomal aberrations were detected in 16 samples: 13 with involvement of 9q22 and 22q11-12, and three with rearrangements of 9q22 and 17q11. Fifteen cases had an EWS/CHN fusion transcript and three had an RBP56/CHN transcript. The most frequent EWS/CHN transcript (type 1; 10 tumors), involved fusion of EWS exon 12 with CHN exon 3, and the second most common (type 5; two cases) was fusion of EWS exon 13 with CHN exon 3. In all tumors with RBP56/CHN fusion, exon 6 of RBP56 was fused to exon 3 of CHN. By genomic XL PCR and sequence analyses, the breakpoints from 14 cases were mapped in the EWS, RBP56, and CHN genes. In CHN, 12 breakpoints were found in intron 2 and only two in intron 1. In EWS, the breaks occurred in introns 7 (one break), 12 (eight breaks), and 13 (one break), and in RBP56 in intron 6. Repetitive elements such as Alu and LINE sequences seem to have limited, if any, importance in the genesis of EWS/CHN and RBP56/CHN chimeras. Furthermore, there were no chi, chi-like, topoisomerase II, or translin consensus sequences in the introns harboring the translocation breakpoints, nor could the number of topo I sites in EWS, RBP56, and CHN introns explain the uneven distribution of the breakpoints among EWS or CHN introns. Additional genetic events, such as nucleotide insertions, homologies at the junction, deletions, duplications, and inversions, were found to accompany the translocations, indicating that the chromosomal translocations do not require sequence-specific recombinases or extensive homology between the recombined sequences.

Adult↗
PubMed2002

Biology and genetic aspects of gastrointestinal stromal tumors: KIT activation and cytogenetic alterations.

Recent studies have done much to reveal the biological and genetic underpinnings of gastrointestinal stromal tumors (GISTs). Constitutive activation of the KIT receptor tyrosine kinase is a central pathogenetic event in most GISTs and generally results from oncogenic point mutations which can involve either extracellular or cytoplasmic domains of the receptor. Oncogenic mutations enable the KIT receptor to phosphorylate various substrate proteins, leading to activation of signal transduction cascades which regulate cell proliferation, apoptosis, chemotaxis, and adhesion. KIT mutations can be broadly assigned to 2 groups, those that involve the "regulatory" regions responsible for modulating KIT enzymatic activity and those that involve the enzymatic region itself. In vitro studies suggest that GISTs with regulatory-region KIT mutations are more likely to respond to STI-571 than are GISTs with enzymatic-region mutations. A minority of GISTs lack demonstrable KIT mutations, but KIT is nonetheless strongly activated. Such GISTs might contain KIT mutations which are not readily detected by conventional screening methods, or alternately, KIT might be activated by nonmutational mechanisms. Most GISTs have noncomplex cytogenetic profiles, often featuring deletions of chromosomes 14 and 22. Additional chromosomal aberrations are acquired as the GISTs progress to higher histologic grade. These cytogenetic aberrations are undoubtedly important in GIST pathogenesis, but currently they do not play a key role as diagnostic adjuncts.

Chromosome Aberrations↗
PubMed2002

PPARgamma ligands inhibit primary tumor growth and metastasis by inhibiting angiogenesis.

Several drugs approved for a variety of indications have been shown to exhibit antiangiogenic effects. Our study focuses on the PPARgamma ligand rosiglitazone, a compound widely used in the treatment of type 2 diabetes. We demonstrate, for the first time to our knowledge, that PPARgamma is highly expressed in tumor endothelium and is activated by rosiglitazone in cultured endothelial cells. Furthermore, we show that rosiglitazone suppresses primary tumor growth and metastasis by both direct and indirect antiangiogenic effects. Rosiglitazone inhibits bovine capillary endothelial cell but not tumor cell proliferation at low doses in vitro and decreases VEGF production by tumor cells. In our in vivo studies, rosiglitazone suppresses angiogenesis in the chick chorioallantoic membrane, in the avascular cornea, and in a variety of primary tumors. These results suggest that PPARgamma ligands may be useful in treating angiogenic diseases such as cancer by inhibiting angiogenesis.

Angiogenesis Inhibitors↗