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Background: Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors most often caused by activating mutations of the KIT gene. KIT tyrosine kinase inhibitors provide targeted therapy for the underlying genetic mutation, and adjuvant therapy is indicated for patients who are at significant risk of relapse following GIST resection. This is a report of the safety of imatinib in patients with GIST in the adjuvant setting in an expanded access program., Methods: In this multicenter, open-label, single-arm trial, safety was assessed based on the frequency of adverse events (AEs)., Results: Three hundred patients were treated and analyzed; 40 patients discontinued treatment. Median overall exposure during the program was 181 days (range 9-420); most patients (260/300 treated) completed the study. Six patients had disease recurrence, 4 of whom discontinued. In line with previously published reports, the most frequent AEs were nausea, diarrhea, and periorbital edema. The AEs were mild to moderate in most cases (76%)., Conclusions: These findings are in agreement with the known safety profile of imatinib and confirm the safety of imatinib at 400 mg/day in the adjuvant setting. The incidence of severe AEs was low., (© 2019 S. Karger AG, Basel.)

Importance: Little is known about whether the duration of adjuvant imatinib influences the prognostic significance of KIT proto-oncogene receptor tyrosine kinase (KIT) and platelet-derived growth factor receptor α (PDGFRA) mutations., Objective: To investigate the effect of KIT and PDGFRA mutations on recurrence-free survival (RFS) in patients with gastrointestinal stromal tumors (GISTs) treated with surgery and adjuvant imatinib., Design, Setting, and Participants: This exploratory study is based on the Scandinavian Sarcoma Group VIII/Arbeitsgemeinschaft Internistische Onkologie (SSGXVIII/AIO) multicenter clinical trial. Between February 4, 2004, and September 29, 2008, 400 patients who had undergone surgery for GISTs with a high risk of recurrence were randomized to receive adjuvant imatinib for 1 or 3 years. Of the 397 patients who provided consent, 341 (85.9%) had centrally confirmed, localized GISTs with mutation analysis for KIT and PDGFRA performed centrally using conventional sequencing. During a median follow-up of 88 months (completed December 31, 2013), 142 patients had GIST recurrence. Data of the evaluable population were analyzed February 4, 2004, through December 31, 2013., Main Outcomes and Measures: The main outcome was RFS. Mutations were grouped by the gene and exon. KIT exon 11 mutations were further grouped as deletion or insertion-deletion mutations, substitution mutations, insertion or duplication mutations, and mutations that involved codons 557 and/or 558., Results: Of the 341 patients (175 men and 166 women; median age at study entry, 62 years) in the 1-year group and 60 years in the 3-year group), 274 (80.4%) had GISTs with a KIT mutation, 43 (12.6%) had GISTs that harbored a PDGFRA mutation, and 24 (7.0%) had GISTs that were wild type for these genes. PDGFRA mutations and KIT exon 11 insertion or duplication mutations were associated with favorable RFS, whereas KIT exon 9 mutations were associated with unfavorable outcome. Patients with KIT exon 11 deletion or insertion-deletion mutation had better RFS when allocated to the 3-year group compared with the 1-year group (5-year RFS, 71.0% vs 41.3%; P < .001), whereas no significant benefit from the 3-year treatment was found in the other mutational subgroups examined. KIT exon 11 deletion mutations, deletions that involved codons 557 and/or 558, and deletions that led to pTrp557&#95;Lys558del were associated with poor RFS in the 1-year group but not in the 3-year group. Similarly, in the subset with KIT exon 11 deletion mutations, higher-than-the-median mitotic counts were associated with unfavorable RFS in the 1-year group but not in the 3-year group., Conclusions and Relevance: Patients with KIT exon 11 deletion mutations benefit most from the longer duration of adjuvant imatinib. The duration of adjuvant imatinib modifies the risk of GIST recurrence associated with some KIT mutations, including deletions that affect exon 11 codons 557 and/or 558., Trial Registration: clinicaltrials.gov Identifier: NCT00116935.

Purpose: Three years of adjuvant imatinib therapy are recommended for patients with GI stromal tumor (GIST) with high-risk features, according to survival findings in the Scandinavian Sarcoma Group XVIII/AIO (Arbeitsgemeinschaft Internistische Onkologie) trial. To investigate whether the survival benefits have persisted, we performed the second planned analysis of the trial., Patients and Methods: Eligible patients had macroscopically completely excised, KIT-positive GIST with a high risk of recurrence, as determined by using the modified National Institutes of Health criteria. After surgery, the patients were randomly assigned to receive imatinib for either 1 or 3 years. The primary objective was recurrence-free survival (RFS), and the secondary objectives included survival., Results: A total of 400 patients were entered onto this open-label study between February 4, 2004, and September 29, 2008. During a median follow-up of 90 months, 171 recurrences and 69 deaths were detected. Patients assigned to the 3-year group had longer RFS than those assigned to the 1- year group; 5-year RFS was 71.1% versus 52.3%, respectively (hazard ratio [HR], 0.60; 95% CI 0.44 to 0.81; P < .001), and survival was 91.9% versus 85.3% (HR, 0.60; 95% CI, 0.37 to 0.97; P = .036). Patients in the 3-year group survived longer in the subset with centrally confirmed GIST and without macroscopic metastases at study entry (93.4% v 86.8%; HR, 0.53; 95% CI, 0.30 to 0.93; P = .024). Similar numbers of cardiac events and second cancers were recorded in the groups., Conclusion: Three years of adjuvant imatinib therapy results in longer survival than 1 year of imatinib. High 5-year survival rates are achievable in patient populations with high-risk GIST., (© 2015 by American Society of Clinical Oncology.)

Background: Little is known about the factors that predict for gastrointestinal stromal tumor (GIST) recurrence in patients treated with adjuvant imatinib., Methods: Risk factors for GIST recurrence were identified, and 2 risk stratification scores were developed using the database of the Scandinavian Sarcoma Group (SSG) XVIII trial, where 358 patients with high-risk GIST with no overt metastases were randomly assigned to adjuvant imatinib 400 mg/day either for 12 or 36 months after surgery. The findings were validated in the imatinib arm of the American College of Surgeons Oncology Group Z9001 trial, where 359 patients with GIST were randomized to receive imatinib and 354 were to receive placebo for 12 months., Results: Five factors (high tumor mitotic count, nongastric location, large size, rupture, and adjuvant imatinib for 12 months) were independently associated with unfavorable recurrence-free survival (RFS) in a multivariable analysis in the SSGXVIII cohort. A risk score based on these 5 factors had a concordance index with GIST recurrence of 78.9%. When a simpler score consisting of the 2 strongest predictive factors (mitotic count and tumor site) was devised, the groups with the lowest, intermediate high, and the highest risk had 5-year RFS of 76.7%, 47.5%, and 8.4%, respectively. Both scores were strongly associated with RFS in the validation cohort (P < .001 for each comparison)., Conclusions: The scores generated were effective in stratifying the risk of GIST recurrence in patient populations treated with adjuvant imatinib. Patients with nongastric GIST with a high mitotic count are at a particularly high risk for recurrence., (© 2014 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society.)

Purpose: Purpose of the study was to compare radiological treatment response according to RECIST, Choi and volumetry in GIST-patients under 2nd-line-sunitinib-therapy and to correlate the results of treatment response assessment with disease-specific survival (DSS)., Patients and Methods: 20 patients (mean: 60.7 years; 12 male/8 female) with histologically proven GIST underwent baseline-CT of the abdomen under imatinib and follow-up-CTs 3 months and 1 year after change to sunitinib. 68 target lesions (50 hepatic, 18 extrahepatic) were investigated. Therapy response (partial response (PR), stable disease (SD), progressive disease (PD)) was evaluated according to RECIST, Choi and volumetric criteria. Response according to the different assessment systems was compared and correlated to the DSS of the patients utilizing Kaplan-Meier statistics., Results: The mean DSS (in months) of the response groups 3 months after therapy change was: RECIST: PR (0/20); SD (17/20): 30.4 (months); PD (3/20) 11.6. Choi: PR (10/20) 28.6; SD (8/20) 28.1; PD (2/20) 13.5. Volumetry: PR (4/20) 29.6; SD (11/20) 29.7; PD (5/20) 17.2. Response groups after 1 year of sunitinib showed the following mean DSS: RECIST: PR (3/20) 33.6; SD (9/20) 29.7; PD (8/20) 20.3. Choi: PR (10/20) 21.5; SD (4/20) 42.9; PD (6/20) 23.9. Volumetry: PR (6/20) 27.3; SD (5/20) 38.5; PD (9/20) 19.3., Conclusion: One year after modification of therapy, only partial response according to RECIST indicated favorable survival in patients with GIST. The value of alternate response assessment strategies like Choi criteria for prediction of survival in molecular therapy still has to be demonstrated., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Background: The management of primary gastrointestinal stromal tumours (GISTs) has evolved with the introduction of adjuvant therapy. Recently reported results of the SSG XVIII/AIO trial by the Scandinavian Sarcoma Group (SSG) and the German Working Group on Medical Oncology (AIO) represent a significant change in the evidence for adjuvant therapy duration. The objectives of this European Expert Panel meeting were to describe the optimal management and best practice for the systemic adjuvant treatment of patients with primary GISTs., Materials and Methods: A panel of medical oncology experts from European sarcoma research groups were invited to a 1-day workshop. Several questions and discussion points were selected by the organising committee prior to the conference. The experts reviewed the current literature of all clinical trials available on adjuvant therapy for primary GISTs, considered the quality evidence and formulated recommendations for each discussion point., Results: Clinical issues were identified and provisional clinical opinions were formulated for adjuvant treatment patient selection, imatinib dose, duration and patient recall, mutational analysis and follow-up of primary GIST patients. Adjuvant imatinib 400 mg/day for 3 years duration is a standard treatment in all patients with significant risk of recurrence following resection of primary GISTs. Patient selection for adjuvant therapy should be based on any of the three commonly used patient risk stratification schemes. R1 surgery (versus R0) alone is not an indication for adjuvant imatinib in low-risk GIST. Recall and imatinib restart could be proposed in patients who discontinued 1-year adjuvant imatinib within the previous 3 months and may be considered on a case-by-case basis in patients who discontinued within the previous year. Mutational analysis is recommended in all cases of GISTs using centralised laboratories with good quality control. Treatment is not recommended in an imatinib-insensitive D842V-mutated GIST. During adjuvant treatment, patients are recommended to be clinically assessed at 1- to 3-month intervals. Upon discontinuation, computed tomography scan (CT) scans are recommended every 3 to 4 months for 2 years when the risk of relapse is highest, followed by every 6 months until year 5 and annually until year 10 after treatment discontinuation., Conclusions: Key points in systemic adjuvant treatment and clinical management of primary GISTs as well as open questions were identified during this European Expert Panel meeting on GIST management.

Background: This phase III open-label trial investigated the efficacy of nilotinib in patients with advanced gastrointestinal stromal tumors following prior imatinib and sunitinib failure., Patients and Methods: Patients were randomized 2:1 to nilotinib 400 mg b.i.d. or best supportive care (BSC; BSC without tyrosine kinase inhibitor, BSC+imatinib, or BSC+sunitinib). Primary efficacy end point was progression-free survival (PFS) based on blinded central radiology review (CRR). Patients progressing on BSC could cross over to nilotinib., Results: Two hundred and forty-eight patients enrolled. Median PFS was similar between arms (nilotinib 109 days, BSC 111 days; P=0.56). Local investigator-based intent-to-treat (ITT) analysis showed a significantly longer median PFS with nilotinib (119 versus 70 days; P=0.0007). A trend in longer median overall survival (OS) was noted with nilotinib (332 versus 280 days; P=0.29). Post hoc subset analyses in patients with progression and only one prior regimen each of imatinib and sunitinib revealed a significant difference in median OS of >4 months in favor of nilotinib (405 versus 280 days; P=0.02). Nilotinib was well tolerated., Conclusion: In the ITT analysis, no significant difference in PFS was observed between treatment arms based on CRR. In the post hoc subset analyses, nilotinib provided significantly longer median OS.

Purpose: Effective and safe treatment options are needed for patients with advanced gastrointestinal stromal tumors (GIST) who are initially unresponsive to the tyrosine kinase inhibitor (TKI) imatinib, or develop acquired secondary imatinib resistance., Case Report: We report a 39-year-old woman with primary rectal GIST who underwent abdominoperineal resection in December 2004, achieving R0 margins. In August 2009, the patient was referred to our clinic, and we detected metastatic GIST of the liver, as well as peritoneal and gluteal lesions. The patient was treated with imatinib 400 mg/day for 3 weeks and subsequently switched to nilotinib (400 mg bid) after enrolling in a clinical trial. After 8 weeks of nilotinib treatment, a response was observed in the liver metastasis, and metabolic activity was no longer detected. Also, the gluteal and peritoneal lesions were no longer detected. After 16 weeks of nilotinib treatment, a cystic mass was identified in the liver metastasis. Tumor rupture was considered a strong possibility, prompting resection of the liver metastasis. Greater than 80% of the resected tumor mass was necrotic, consistent with the lack of metabolism observed 8 weeks prior. The patient resumed nilotinib treatment (400 mg bid) shortly after surgery and continues treatment while remaining disease-free for more than 9 months with normal liver function., Conclusion: This is the first report demonstrating the feasibility of nilotinib (400 mg bid) for the first-line treatment of metastatic GIST. Furthermore, these results underscore that responses to TKIs may be underestimated by Response Evaluation Criteria in Solid Tumors.

Context: Adjuvant imatinib administered for 12 months after surgery has improved recurrence-free survival (RFS) of patients with operable gastrointestinal stromal tumor (GIST) compared with placebo., Objective: To investigate the role of imatinib administration duration as adjuvant treatment of patients who have a high estimated risk for GIST recurrence after surgery., Design, Setting, and Patients: Patients with KIT-positive GIST removed at surgery were entered between February 2004 and September 2008 to this randomized, open-label phase 3 study conducted in 24 hospitals in Finland, Germany, Norway, and Sweden. The risk of GIST recurrence was estimated using the modified National Institutes of Health Consensus Criteria., Intervention: Imatinib, 400 mg per day, orally for either 12 months or 36 months, started within 12 weeks of surgery., Main Outcome Measures: The primary end point was RFS; the secondary end points included overall survival and treatment safety., Results: Two hundred patients were allocated to each group. The median follow-up time after randomization was 54 months in December 2010. Diagnosis of GIST was confirmed in 382 of 397 patients (96%) in the intention-to-treat population at a central pathology review. KIT or PDGFRA mutation was detected in 333 of 366 tumors (91%) available for testing. Patients assigned for 36 months of imatinib had longer RFS compared with those assigned for 12 months (hazard ratio [HR], 0.46; 95% CI, 0.32-0.65; P < .001; 5-year RFS, 65.6% vs 47.9%, respectively) and longer overall survival (HR, 0.45; 95% CI, 0.22-0.89; P = .02; 5-year survival, 92.0% vs 81.7%). Imatinib was generally well tolerated, but 12.6% and 25.8% of patients assigned to the 12- and 36-month groups, respectively, discontinued imatinib for a reason other than GIST recurrence., Conclusion: Compared with 12 months of adjuvant imatinib, 36 months of imatinib improved RFS and overall survival of GIST patients with a high risk of GIST recurrence., Trial Registration: clinicaltrials.gov Identifier: NCT00116935.

Background: Studies on gastrointestinal stromal tumours (GIST) in the paediatric population are limited to case reports or small case series., Patients and Methods: We conducted a retrospective study to describe the long-term outcome of children and adolescents with GIST registered in the database of the Cooperative Weichteilsarkom Studiengruppe (CWS)., Results: Sixteen patients (female, n = 11) were identified. Median age at diagnosis was 13.5 years. In four female patients presence of thoracic masses in addition to GIST led to the diagnosis of complete or incomplete Carney triad. Three female patients had metastatic disease at diagnosis, the remaining thirteen GIST were localised. The stomach was the most common primary site of the tumour, followed by the small bowel and colon/abdomen. All patients underwent tumour resection. Receptor tyrosine kinase inhibitors (RTKI) were administered in five patients. With a median follow-up of 96 months all patients are alive, nine of them in first CR. Four female patients developed local or distant recurrence; three of them achieved second CR and one a PR. Two individuals have extensive progressive (n = 1) or stable (n = 1) disease. Estimated progression-free survival at 5 years is 0.63 (95%CI: 0.50-0.86)., Conclusions: Although long-term overall survival is favourable, approximately 30 percent of patients develop disease progression. International cooperation in registration, tissue collection and molecular studies are required to obtain reliable data on the clinical course of these rare tumours in the paediatric population. Biological studies are a prerequisite for initiation of studies with RTKI., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Gastrointestinal stromal tumors (GIST) are mesenchymal tumors that in the past were classified as leiomyosarcomas or leiomyomas not responding to standard sarcoma chemotherapy. In several phase I and II trials the efficacy and safety of imatinib was shown before the largest trial ever performed in a single sarcoma entity revealed response rates (CR/PR) of 52 %. This multicenter phase II trial presented here was performed to open access to imatinib for patients with unresectable or metastastatic GIST when the EORTC 62005 trial had been closed before imatinib was approved in Germany. It was designed to follow the best clinical response and to assess the efficacy, safety and tolerability of imatinib 400mg/d in patients with unresectable or metastatic gastrointestinal stromal tumor. - 95 patients were treated in this trial with Imatinib 400mg/d. Four patients (4.6 %) attained a complete response and 26 patients (29.9%) a partial response to imatinib treatment. Forty-one patients (47.1 %) revealed a stable disease and 16 patients (18.4 %) had a progressive disease. - Of the progressive patients 22% showed a partial response and 67 % showed stable disease after escalating the dose to 800 mg. According to SWOG tumor response classification, 66 patients (70%) were free of progression within the first year of treatment. - Seventy-one patients (74.7%) experienced adverse events or severe adverse events with a suspected relationship to the study drug. Among these, the most common were nausea (n=27 patients, 28.4 %), eyelid edema and peripheral edema in 23 patients each (24.2 %), diarrhea in 20 patients (21.1 %), muscle cramps in 15 patients (15.8 %) and fatigue in 13 patients (13.7 %). - Imatinib 400 mg/d led to disease stabilisation in 81,6% of patients with unresectable or metastatic malignant GIST. Thirty-four percent of patients attained a tumor remission (partial or complete response). The safety profile of imatinib based on adverse event assessment is favorable. Imatinib is generally well tolerated in patients with gastrointestinal stromal tumors.

Purpose: Advanced gastrointestinal stromal tumours (GISTs) are treated with tyrosine kinase inhibitors, which also have antiangiogenic properties. Dual-energy CT (DECT) allows to acquire semi-quantitative iodine images which might correlate with blood pool and tumor vascularity. In this feasibility-study, we correlated lesional iodine uptake estimations in correlation to tumor size changes under targeted therapy as first step in the evaluation of dedicated DECT based strategies for monitoring molecular therapies in GIST., Patients and Methods: 48 tumor lesions in 18 patients with metastasized histologically proven GIST under tyrosine kinase inhibitor (TKI) therapy were analyzed. Patients were examined with a dual-source CT in dual-energy mode (Voltage tube A: 80 kV, tube B: 140 kV). Using the dual-energy software virtual unenhanced, selective iodine (overlay) and mixed CT numbers (similar to CT numbers at 120 kV) of lesions were calculated. The largest diameter of each lesion on cross-sectional axial images was measured. The mean difference of overlay CT numbers in the baseline and follow-up examinations was calculated and this marker of lesional iodine uptake was compared to lesional size changes under molecular therapy., Results: Utilizing the cut-off value 15 HU of change in overlay, DECT allowed to identify lesions with a stable, increased or decreased lesional iodine uptake with corresponding typical lesion size change patterns after 3 months of targeted therapy: 30 lesions had no significant change of overlay CT numbers (OL) (mean: -2.4 HU) or lesion size (mean: +1.5%). A strong decline of the OL (mean: - 24 HU) in 13 lesions was combined with a pronounced growth (mean: + 26%). 5 lesions showed a strong increase of the absolute OL (mean: + 23 HU) associated with a moderate increase in size (+ 8%)., Conclusion: Determination of the overlay CT number with DECT enables to stratify metastases with stable, increasing or decreasing iodine uptake over time with -in our collective- typical lesion size change patterns. Investigation of a larger patient cohort, comparison to histology, alternate imaging biomarkers and correlatrion to long-term response will further clarify the significance of these findings for monitoring targeted therapies in GIST.

Rationale and Objective: The aim of this pilot study was the evaluation of CT perfusion patterns in metastatic GIST lesions under specific molecular therapy with sunitinib or imatinib both in responders and non-responders., Patients and Methods: 24 patients with metastatic GIST under tyrosine kinase inhibition were retrospectively evaluated. A total of 46 perfusion and venous phase CT scans were acquired. Volume of distribution, blood flow, blood volume, permeability and hepatic perfusion index measurements of metastatic lesions were carried out. Lesions were classified as "good response" or "poor response" to therapy, and perfusion parameters were compared for these two types of lesions., Results: 24 patients were evaluated. In the extrahepatic abdominal lesions (N = 15), good responders showed significant lower perfusion values than poor responders (volume of distribution: 3.3 ± 2.0 vs. 13.0 ± 1.8 ml/100ml, p = 0.001). The same tendency was observed in intrahepatic lesions (N = 31) (liver volume of distribution: 2.1 ± 0.3 vs. 7.1 ± 1.3 ml/100ml, p = 0.003); (hepatic perfusion index: 24.3 ± 7.9 vs. 76.1 ± 1.5%, p = 0.0001)., Conclusion: Our data indicate that there are characteristic perfusion patterns of metastatic GIST lesions showing a good or poor response to molecular pharmacotherapy. Perfusion should be further evaluated in cross-sectional imaging studies as a possible biomarker for treatment response in targeted therapies of GIST., (Copyright © 2009 Elsevier Ireland Ltd. All rights reserved.)

Background: Sunitinib inhibits KIT and other members of the split-kinase-domain family of receptor tyrosine kinases. Sunitinib prolongs survival in adult patients with imatinib-resistant gastrointestinal stromal tumor (GIST). We report the experience with sunitinib in pediatric patients with advanced GIST following failure of imatinib., Procedure: Sunitinib therapy was provided through a treatment-use protocol. Patients were 10-17 years old at enrollment. All patients had GIST resistant to imatinib therapy. Sunitinib was administered daily for 4 weeks in 6-week treatment cycles. KIT and platelet-derived growth factor receptor alpha (PDGFRA) genotyping of tumor tissue were performed., Results: One patient achieved a partial response, five patients had stable disease and one patient had progressive disease on sunitinib. The duration of disease stabilization was between 7 and 21+ months, with a mean of 15 months. Time to tumor progression was longer on sunitinib than on prior imatinib treatment for five of six patients. Two patients experienced grade 3 adverse events. All other adverse events were grade 1-2. None of the five patients tested had mutations in KIT or PDGFRA., Conclusion: Sunitinib treatment was associated with substantial initial antitumor activity and acceptable tolerability in this group of pediatric patients with imatinib-resistant GIST., ((c) 2009 Wiley-Liss, Inc.)

Gastrointestinal stromal tumors (GISTs) are most often associated with oncogenic mutations of the KIT gene resulting in activation of the tyrosine kinase receptor KIT. Familial GIST syndrome based on a hereditary predisposition to develop GIST owing to a germline mutation is exceedingly rare. We describe a kindred with familial GIST displaying a novel germline mutation in exon 17. Three siblings (2 females, 1 male; 42 to 49 y) underwent surgery for multiple intra-abdominal tumors within a 3-year period. Their father had been operated on for gastric and jejunal tumors 20 years previously. The GIST was confirmed by immunohistochemistry in each sibling. Tumor and blood samples of the family members were analyzed for mutations in KIT and platelet-derived growth factor receptor (PDGFRalpha) genes. All examined lesions were of spindle cell type with expression of CD117. The tumor material exhibited a novel point mutation in codon 822 in exon 17 resulting in the replacement of asparagine by tyrosine (N822Y). The same mutation was detected in the father's blood sample. One healthy brother of the 3 siblings showed a wild-type sequence of the KIT gene. The germline mutation in exon 17 of the KIT gene identified in this kindred is very different from previously reported mutations of the KIT gene in familial GIST. Although the penetrance of KIT mutations is as yet unknown, assessment of the unaffected kindred of GIST patients for the presence of this mutation could help to distinguish individuals at high risk from those at virtually no risk.

A recent randomized EORTC phase III trial, comparing two doses of imatinib in patients with advanced gastrointestinal stromal tumours (GISTs), reported dose dependency for progression-free survival. The current analysis of that study aimed to assess if tumour mutational status correlates with clinical response to imatinib. Pre-treatment samples of GISTs from 377 patients enrolled in phase III study were analyzed for mutations of KIT or PDGFRA by combination of D-HPLC and direct sequencing of tumour genomic DNA. Mutation types were correlated with patients' survival data. The presence of exon 9-activating mutations in KIT was the strongest adverse prognostic factor for response to imatinib, increasing the relative risk of progression by 171% (P<0.0001) and the relative risk of death by 190% (P<0.0001) when compared with KIT exon 11 mutants. Similarly, the relative risk of progression was increased by 108% (P<0.0001) and the relative risk of death by 76% (P=0.028) in patients without detectable KIT or PDGFRA mutations. In patients whose tumours expressed an exon 9 KIT oncoprotein, treatment with the high-dose regimen resulted in a significantly superior progression-free survival (P=0.0013), with a reduction of the relative risk of 61%. We conclude that tumour genotype is of major prognostic significance for progression-free survival and overall survival in patients treated with imatinib for advanced GISTs. Our findings suggest the need for differential treatment of patients with GISTs, with KIT exon 9 mutant patients benefiting the most from the 800 mg daily dose of the drug.

Purpose: The aim of this study was to identify factors predicting initial and late resistance of GI stromal tumor (GIST) patients to imatinib and to document the dose-response relationship in the prognostic subgroups. This study is based on the European Organisation for Research and Treatment of Cancer-Italian Sarcoma Group-Australasian Gastrointestinal Trials Group randomized trial comparing two doses of imatinib in advanced disease., Patients and Methods: Initial resistance was defined as progression within 3 months of randomization, and late resistance was defined as progression beyond 3 months. Investigated cofactors include imatinib dose, age, sex, performance status, original disease site, site and size of lesions at trial entry, and baseline hematologic and biologic parameters., Results: Initial resistance was recorded for 116 (12%) of 934 assessable patients and was independently predicted by the presence of lung and absence of liver metastases, low hemoglobin level, and high granulocyte count. Among 818 patients who were alive and progression free at 3 months, 347 subsequent progressions were recorded, and late resistance was independently predicted by high baseline granulocyte count, primary tumor outside of the stomach, large tumor size, and low initial imatinib dose. The impact of initial dose on late resistance was mainly significant in patients with a high baseline granulocyte count (> 5.10(9)/L) and in patients with tumors of GI origin outside of the stomach and small intestine., Conclusion: Our study identifies patients for whom initial and/or long-term treatment needs to be improved and patients who require a high initial dose. Correlation of these results with immunohistochemistry and molecular parameters may further help to understand the biologic mechanisms of resistance.

In the EORTC-ISG-AGITG trial 946 patients with advanced gastro-intestinal stromal tumours (GIST) were randomised to receive 400 or 800 mg of imatinib daily. An increase in progression free survival (PFS) was demonstrated for patients randomised to the high-dose arm. Patients randomised to low-dose could cross-over to high-dose upon progression. We evaluated the feasibility, safety and efficacy of this policy. Of the 241 patients available for follow-up, 133 patients (55%) crossed over to high-dose imatinib according to the protocol. Of these patients, 92% had not had a prior dose reduction. The cumulative incidence of subsequent dose reductions after cross-over was 17% after six months with 51% discontinuing therapy without requiring a dose reduction. The extent of anaemia and fatigue increased significantly after cross-over, whilst neutropenia was less severe than during low-dose treatment. Objective responses after cross-over included three patients (2%) with a partial response and 36 (27%) with stable disease. The median PFS after cross-over was 81 days, although 18.1% of patients were still alive and progression free one year after cross-over. We conclude that a cross-over to high-dose imatinib is feasible and safe in GIST patients who progress on low-dose therapy.