Outcome of patients with advanced gastro-intestinal stromal tumours crossing over to a daily imatinib dose of 800 mg after progression on 400 mg

Clinical practice guidelines for gastrointestinal stromal tumor (GIST) in Japan: English version

Diagnostic and treatment strategies for gastrointestinal stromal tumors (GISTs) have evolved greatly since the introduction of molecularly targeted therapies. Although several clinical practice guidelines are extant, such as those published by the National Comprehensive Cancer Network and the European Society of Medical Oncology, it is not clear as to whether these are appropriate for clinical practice in Japan. Therefore, clinical practice guidelines for the optimal diagnosis and treatment of GIST tailored for the Japanese situation have often been requested. For this reason, the Japanese Clinical Practice Guideline for GIST was proposed by the GIST Guideline Subcommittee, with the official approval of the Clinical Practice Guidelines Committee for Cancer of the Japan Society of Clinical Oncology (JSCO), and was published after assessment by the Guideline Evaluation Committee of JSCO. The GIST Guideline Subcommittee consists of members from JSCO, the Japanese Gastric Cancer Association (JGCA), and the Japanese Study Group on GIST, with the official approval of these organizations. The GIST Guideline Subcommittee is not influenced by any other organizations or third parties. Revision of the guideline may be done periodically, with the approval of the GIST Guideline Subcommittee, either every 3 years or when important new evidence that might alter the optimal diagnosis and treatment of GIST emerges. Here we present the English version of the Japanese Clinical Practice Guideline for GIST prepared by the GIST Guideline Subcommittee.

Gastrointestinal stromal tumors: key to diagnosis and choice of therapy

The common feature of gastrointestinal stromal tumors (GISTs) is the expression of KIT protein or acquisition of activating, constitutive mutations in the KIT or platelet-derived growth factor receptor alpha (PDGFRA) genes that are the early oncogenic events during GIST development. With these discoveries, GIST has emerged as a distinct sarcoma entity, enabling the introduction of targeted therapy using the inhibition of KIT/PDGFRA and their downstream signaling cascade. The introduction of a small-molecule tyrosine kinase inhibitor, imatinib mesylate, to clinical practice has revolutionized the treatment of patients with advanced GISTs and is currently approved as first-line treatment for patients with metastatic and/or inoperable GISTs. Mutation screening is currently a tool in GIST diagnosis, assessment of sensitivity to tyrosine kinase inhibitors, and prediction of achieving response to molecularly targeted therapy. This article discusses the histologic and molecular criteria for distinguishing GISTs from other types of sarcoma, and the molecular diagnostic tools that are currently available or in development to assist in therapy decisions.

Response of Carney's triad‐related metastatic gastrointestinal stromal tumor to sunitinib

Background:  Metastatic Carney's triad is a rare syndrome of gastrointestinal stromal tumour, paraganglioma and pulmonary chondroma associated with unique clinical behavior and relative resistance to imatinib

Case:  A 50‐year‐old woman was diagnosed with metastatic gastrointestinal stromal tumour, after having complete remission for almost three decades following gastrectomy for her original gastric tumour. She was c‐kit‐wild type and developed various paragangliomas and possible pulmonary chondromas during the course of her disease. Treatment with the tyrosine kinase inhibitor imatinib mesylate and subsequently the multikinase inhibitor sunitinib were associated with periods of radiological response and clinical benefit before the patient died of progressive disease.

Conclusion:  Identification of patients with Carney's triad tumours is important in clinical practice as they have distinct clinical behavior, mutational status and relative lack of responsiveness to the current available targeted therapy compared to the typical c‐kit positive gastrointestinal stromal tumours.

Management of gastrointestinal stromal tumors

A gastrointestinal stromal tumor (GIST) is a rare mesenchymal malignancy of the gastrointestinal (GI) tract. Malignant GISTs were first defined as a separate entity from a collection of nonepithelial malignancies of the GI tract in the 1980s and 1990s based on pathologic and clinical behavior. The discovery of activating KIT mutations as a near-uniform occurrence in these tumors greatly influenced the classification [1] and revolutionized therapeutic management of these tumors. To meet the next challenges, newer tyrosine kinase inhibitors and targeted agents are being developed with the goal of providing improved response rates or alternative therapies for patients progressing on established agents. In this article, the authors describe the management of GISTs, concentrating on surgical management and targeted therapies.

Surgical intervention following imatinib treatment in patients with advanced gastrointestinal stromal tumors (GISTs)

BACKGROUND

We investigated the role of surgical intervention for advanced GIST after imatinib.

METHODS

Among 256 patients treated with imatinib for advanced GIST, the medical records of the 34 patients who underwent surgery of residual tumors after imatinib treatment were reviewed.

RESULTS

Surgery was performed on 24 patients with responsive disease (RD) after imatinib, on 3 with focal progressive disease (FP), and on 7 with generalized progressive disease (GP). All gross tumors were completely resected in 19/24 (79%), 1/3 (33%), and 1/7 (14%) patients, respectively. Disease status at surgery was associated with prognosis after surgery; with a median follow-up of 25.7 months, the median progression-free survival of patients resected for RD, FP, and GP were 27.8 months (95% CI, 17.8-37.8 months), 5.1 months (95% CI, 4.7-5.6 months), and 3.3 months (95% CI, 2.7-3.9 months), respectively (P < 0.001). Median overall survival was not reached in patients resected for RD, and was 22.5 months (95% CI, 1.4-43.0 months) and 23.5 months (95% CI, 3.0-43.9) for patients resected for FP and GP, respectively (P < 0.001).

CONCLUSION

Surgical resection of tumors responsive to imatinib may be beneficial in patients with advanced GIST. Debulking surgery, however, is not recommended for patients who have already developed imatinib resistance.

Advances in the treatment of gastrointestinal stromal tumours

Imatinib, a selective tyrosine kinase inhibitor, is currently the standard of care first-line treatment for unresectable or metastatic gastrointestinal stromal tumour (GIST), improving survival time and delaying disease progression in many patients. Nevertheless, primary and secondary (acquired) resistance to imatinib is a substantial problem in routine clinical practice. Sunitinib is an oral, multitargeted tyrosine kinase inhibitor that was approved for the treatment of imatinib-resistant or -intolerant GIST. In the pivotal phase III study, sunitinib provided substantial clinical benefits including disease control and superior survival versus placebo as second-line treatment. Treatment with sunitinib was reasonably well tolerated. The availability of sunitinib represents an important clinical advance in GIST management, providing physicians and patients with an effective therapy when resistance to imatinib develops.

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.

Relationship of imatinib-free plasma levels and target genotype with efficacy and tolerability

Imatinib has revolutionised the treatment of chronic myeloid leukaemia (CML) and gastrointestinal stromal tumours (GIST). Using a nonlinear mixed effects population model, individual estimates of pharmacokinetic parameters were derived and used to estimate imatinib exposure (area under the curve, AUC) in 58 patients. Plasma-free concentration was deduced from a model incorporating plasma levels of alpha₁-acid glycoprotein. Associations between AUC (or clearance) and response or incidence of side effects were explored by logistic regression analysis. Influence of KIT genotype was also assessed in GIST patients. Both total (in GIST) and free drug exposure (in CML and GIST) correlated with the occurrence and number of side effects (e.g. odds ratio 2.7±0.6 for a two-fold free AUC increase in GIST; P<0.001). Higher free AUC also predicted a higher probability of therapeutic response in GIST (odds ratio 2.6±1.1; P=0.026) when taking into account tumour KIT genotype (strongest association in patients harbouring exon 9 mutation or wild-type KIT, known to decrease tumour sensitivity towards imatinib). In CML, no straightforward concentration–response relationships were obtained. Our findings represent additional arguments to further evaluate the usefulness of individualising imatinib prescription based on a therapeutic drug monitoring programme, possibly associated with target genotype profiling of patients.

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.

Long-term results from a randomized phase II trial of standard- versus higher-dose imatinib mesylate for patients with unresectable or metastatic gastrointestinal stromal tumors expressing KIT

PURPOSE

The outcome of patients diagnosed with advanced gastrointestinal stromal tumor (GIST) and treated long-term with imatinib mesylate is unknown. A previous report of a randomized phase II trial of imatinib mesylate in patients with incurable GIST detailed high response rates at both the 400 and the 600 mg/d dose levels. We conducted a long-term analysis of patients treated on the trial, including patients followed during an extension phase, to evaluate survival, patterns of failure, and potential prognostic factors, including tumor mutational status.

PATIENTS AND METHODS

Patients with advanced GIST were enrolled onto an open-label, multicenter trial and were randomly assigned (1:1) to receive imatinib 400 versus 600 mg/d. Data were prospectively collected on KIT mutational status, total tumor area, and other potential prognostic factors. Patients were followed for a median of 63 months.

RESULTS

One hundred forty-seven patients were enrolled: 73 were in arm A (imatinib 400 mg/d), and 74 were in arm B (imatinib 600 mg/d). Response rates, median progression-free survival, and median overall survival were essentially identical on both arms, and median survival was 57 months for all patients. Forty-one patients overall (28%) remained on the drug long-term. Female sex, the presence of an exon 11 mutation, and normal albumin and neutrophil levels were independently associated with better survival.

CONCLUSION

Nearly 50% of patients with advanced GIST who were treated with imatinib mesylate survived for more than 5 years, regardless of a 400 or 600 mg/d starting dose.

Phase III Randomized, Intergroup Trial Assessing Imatinib Mesylate At Two Dose Levels in Patients With Unresectable or Metastatic Gastrointestinal Stromal Tumors Expressing the Kit Receptor Tyrosine Kinase: S0033

Purpose

To assess potential differences in progression-free or overall survival when imatinib mesylate is administered to patients with incurable gastrointestinal stromal tumors (GIST) at a standard dose (400 mg daily) versus a high dose (400 mg twice daily).

Patients and Methods

Patients with metastatic or surgically unresectable GIST were eligible for this phase III open-label clinical trial. At registration, patients were randomly assigned to either standard or high-dose imatinib, with close interval follow-up. If objective progression occurred by Response Evaluation Criteria in Solid Tumors, patients on the standard-dose arm could reregister to the trial and receive the high-dose imatinib regimen.

Results

Seven hundred forty-six patients with advanced GIST from 148 centers across the United States and Canada were enrolled onto this trial in 9 months. With a median follow-up of 4.5 years, median progression-free survival was 18 months for patients on the standard-dose arm, and 20 months for those receiving high-dose imatinib. Median overall survival was 55 and 51 months, respectively. There were no statistically significant differences in objective response rates, progression-free survival, or overall survival. After progression on standard-dose imatinib, 33% of patients who crossed over to the high-dose imatinib regimen achieved either an objective response or stable disease. There were more grade 3, 4, and 5 toxicities noted on the high-dose imatinib arm.

Conclusion

This trial confirms the effectiveness of imatinib as primary systemic therapy for patients with incurable GIST but did not show any advantage to higher dose treatment. It appears reasonable to initiate therapy with 400 mg daily and to consider dose escalation on progression of disease.

Optimizing the dose of imatinib for treatment of gastrointestinal stromal tumours: lessons from the phase 3 trials

Imatinib therapy for unresectable or metastatic gastrointestinal stromal tumour (GIST) is typically initiated at a dosage of 400mg/d. Two phase 3 studies investigated whether the higher dose of 800 mg/d - administered initially or upon progression on the 400-mg dose - would improve outcomes. Both the studies confirmed the 400mg/d starting dose for most patients. However, two groups benefited from the treatment with 800 mg/d of imatinib: patients with disease progression on standard-dose therapy, and patients whose tumour harbours an exon 9 mutation in KIT. Initial treatment with 800 mg/d of imatinib (400mg BID) should be considered for patients with KIT exon 9-mutant GIST. In unselected patients, dose optimisation to 800 mg/d may be warranted as a first step in managing progressive disease; such patients should be closely monitored.

Focal progression in patients with gastrointestinal stromal tumors after initial response to imatinib mesylate: a three-center-based study of 38 patients

BACKGROUND

This study aimed to investigate the outcome of patients with advanced gastrointestinal stromal tumors (GISTs) exhibiting focal disease progression during imatinib therapy, treated by surgical resection and imatinib continuation.

METHODS

A consecutive series of 38 patients with metastatic GISTs who underwent treatment with imatinib at our centers during a defined period of time was evaluated. Patients were evaluated for demographics including tumor-related features, initial response, disease recurrence, and salvage treatment modalities, and were classified as having either focal or generalized progression upon presentation prior to salvage therapy.

RESULTS

After a median follow-up of 31.8 months, 25 of the 38 (65.8%) patients had progressed. Nine (36%) patients were classified as having focal and 16 (64%) as having generalized progression. Salvage therapies were: surgical resection and imatinib dose escalation in patients exhibiting focal progression and imatinib dose escalation alone in the majority of patients exhibiting generalized progression. Focal progression was associated with prolonged progression-free survival (PFS) and overall survival (OS) after salvage therapy as compared with generalized progression (median PFS and OS, 11.3 months and not attained, versus 2.5 and 22.8 months, respectively). Six-month PFS was 89% and 39% in patients exhibiting focal and generalized progression, respectively. KIT mutation analysis of controlled and progressive lesions was performed in 4 patients with focal progression. Secondary KIT mutations affected progressive lesions, whereas nonprogressive lesions harbored the original mutations only.

CONCLUSION

Patients with advanced GIST exhibiting focal disease progression during imatinib therapy may benefit from surgical resection and imatinib continuation. Imatinib resistance seems to be partial in these patients.

Pharmacogenetics and stomach cancer: an update

Although new drugs and association regimens have been used in recent years, the chemotherapeutic outcome for gastric cancer is still poor and improvement in patient survival is not satisfactory. Pharmacogenetics could represent a useful approach to optimize chemotherapeutic treatments in order to identify individuals that are true candidates for clinical benefits from therapy, avoiding the development of severe side effects. The most recent update regarding gastric cancer pharmacogenetics highlights a prominent role of genetic polymorphisms of thymidylate synthase and glutathione S-transferase in the pharmacological treatment with commonly used drugs, such as 5-fluorouracil and platinum derivatives. In order to validate the genetic markers, further larger scale and controlled studies are required. A future challenge is represented by the introduction of targeted therapy in gastric cancer treatment, with the potential emerging tool of pharmacogenetic impact on this field.

Pharmacokinetic investigation of imatinib using accelerator mass spectrometry in patients with chronic myeloid leukemia

PURPOSE

To investigate the potential use of accelerator mass spectrometry (AMS) in the study of the clinical pharmacology of imatinib.

EXPERIMENTAL DESIGN

Six patients who were receiving imatinib (400 mg/d) as part of their ongoing treatment for chronic myeloid leukemia (CML) received a dose containing a trace quantity (13.6 kBq) of (14)C-imatinib. Blood samples were collected from patients before and at various times up to 72 h after administration of the test dose and were processed to provide samples of plasma and peripheral blood lymphocytes (PBL). Samples were analyzed by AMS, with chromatographic separation of parent compound from metabolites. In addition, plasma samples were analyzed by liquid chromatography/mass spectrometry (LCMS).

RESULTS

Analysis of the AMS data indicated that imatinib was rapidly absorbed and could be detected in plasma up to 72 h after administration. Imatinib was also detectable in PBL at 24 h after administration of the (14)C-labeled dose. Comparison of plasma concentrations determined by AMS with those derived by LCMS analysis gave similar average estimates of area under plasma concentration time curve (26 +/- 3 versus 27 +/- 11 microg/mL.h), but with some variation within each individual.

CONCLUSIONS

Using this technique, data were obtained in a small number of patients on the pharmacokinetics of a single dose of imatinib in the context of chronic dosing, which could shed light on possible pharmacologic causes of resistance to imatinib in CML.

Drug Insight: advances in renal cell carcinoma and the role of targeted therapies

In metastatic renal cell carcinoma (RCC) immunotherapy results in a small but important improvement in overall survival, but a need exists to develop more-effective systemic therapies. Recent developments in our understanding of the molecular biology of RCC have identified several pathways associated with the development of the disease. A number of strategies designed specifically to target these pathways have resulted. Initial studies have shown marked clinical benefits of so-called 'targeted therapies'. Sunitinib, sorafenib and axitinib are kinase inhibitors that inhibit the VEGF, platelet-derived growth factor and c-kit receptor tyrosine kinases. Bevacizumab is a monoclonal antibody that is directed against VEGF. Temsirolimus inhibits the mammalian target of rapamycin. These agents have all shown considerable activity with manageable toxicity in phase II and III studies in both previously treated and untreated patients. In phase III studies, sorafenib and bevacizumab have been associated with prolonged progression-free survival compared with placebo. Phase III data have shown improvements in progression-free and overall survival with sunitinib and temsirolimus, respectively, compared with interferon alfa. Additional studies are needed to determine the optimum utilization of these agents at the appropriate stage of disease and in the best combinations for maximal clinical benefit.

Second line therapies for the treatment of gastrointestinal stromal tumor

PURPOSE OF REVIEW

Most gastrointestinal stromal tumors eventually acquire resistance to imatinib mesylate. This review focuses on recent progress on management of patients whose disease progresses on the standard dose of imatinib.

RECENT FINDINGS

Approximately 30% of patients failing standard-dose imatinib achieve disease stabilization with high-dose imatinib, but objective responses are few and the clinical benefit usually short-lived. Patients receiving enzyme-inducing drugs may need high imatinib doses to achieve therapeutic blood concentrations. Surgical excision of a single growing metastasis leads to a median progression-free survival time of 7-11 months. Sunitinib malate is effective following imatinib failure. The median time to disease progression is approximately 6 months with sunitinib therapy versus 6 weeks with placebo following discontinuation of imatinib, but few (5%) patients achieve objective response. Patients with gastrointestinal stromal tumor with KIT exon 9 mutation may benefit more from sunitinib than those with exon 11 mutation. Sunitinib frequently causes abnormal thyroid function.

SUMMARY

Sunitinib is now the approved second line therapy following imatinib failure and for patients intolerant to imatinib. The clinical benefit is only moderate, and thyroid function monitoring is required. Several investigational agents are being evaluated for imatinib-resistant gastrointestinal stromal tumor. Palliative procedures, such as hepatic arterial embolization, also require study.

Improved Insight into Resistance Mechanisms to Imatinib in Gastrointestinal Stromal Tumors: A Basis for Novel Approaches and Individualization of Treatment

Gastrointestinal stromal tumor (GIST) is one of the first solid tumor types in which a tyrosine kinase inhibitor, imatinib, has become standard of care for patients with advanced disease. Although imatinib yields antitumor activity in the vast majority of patients, it is likely that all patients eventually experience progressive disease given enough time. In recent years, major progress has been made in the elucidation of mechanisms conferring resistance to imatinib that result in progressive disease. Insight into these resistance mechanisms has already resulted in the availability of strategies that can be applied in cases of progressive disease and it is likely that more approaches will be defined in the next years. Additionally, it can be anticipated that in the near future treatment will be guided according to factors determining sensitivity to imatinib. This review focuses on the factors inducing imatinib resistance that have been elucidated so far, the currently available and potential novel treatment options for patients with progressive disease, and how insight into resistance mechanisms may allow individualized treatment in the near future for patients with advanced GISTs.

Gastrointestinal stromal tumour

Gastrointestinal stromal tumours are the most common mesenchymal neoplasm of the gastrointestinal tract and are highly resistant to conventional chemotherapy and radiotherapy. Such tumours usually have activating mutations in either KIT (75-80%) or PDGFRA (5-10%), two closely related receptor tyrosine kinases. These mutations lead to ligand-independent activation and signal transduction mediated by constitutively activated KIT or PDGFRA. Targeting these activated proteins with imatinib mesylate, a small-molecule kinase inhibitor, has proven useful in the treatment of recurrent or metastatic gastrointestinal stromal tumours and is now being tested as an adjuvant or neoadjuvant. However, resistance to imatinib is a growing problem and other targeted therapeutics such as sunitinib are available. The important interplay between the molecular genetics of gastrontestinal stromal tumour and responses to targeted therapeutics serves as a model for the study of targeted therapies in other solid tumours.

Practical aspects of managing gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are rare tumors of the digestive tract. Despite their rarity, GISTs are of great importance for oncology. Gastrointestinal stromal tumors are one of the first solid tumor types in which specific factors responsible for malignant behavior have been elucidated and for which drugs specifically targeting these factors form the mainstay of treatment in advanced-stage disease. This review addresses several aspects of the current management of GIST as well as some novel developments.

Results of tyrosine kinase inhibitor therapy followed by surgical resection for metastatic gastrointestinal stromal tumor

INTRODUCTION

Gastrointestinal stromal tumor (GIST) is the most common sarcoma of the intestinal tract. Nearly all tumors have an activating mutation in the KIT or, less often, PDGFRalpha, gene. Therapy with tyrosine kinase inhibitors benefits over 80% of patients with advanced GIST, but most patients eventually develop drug resistance.

METHODS

Forty patients with metastatic GIST were treated with tyrosine kinase inhibitors and then underwent surgical resection. Based on the growth of their tumors by serial radiologic imaging, patients were categorized at the time of operation as having responsive disease, focal resistance (1 tumor growing), or multifocal resistance (more than 1 tumor growing). Patients were followed for a median of 15 months (range, 6-46 months) after surgery.

RESULTS

Initially, molecular therapy achieved stable disease or a partial response in all but 1 patient. Surgery was performed after a median of 15 months, and there were no perioperative deaths. After operation, the 20 patients with responsive disease had a 2-year progression-free survival of 61% and 2-year overall survival of 100%. In contrast, the 13 patients with focal resistance progressed after surgery at a median of 12 months and the 2-year overall survival was 36%. There were 7 patients with multifocal resistance and they progressed postoperatively at a median of 3 months and had a 1-year overall survival of 36%.

CONCLUSION

Selected patients with metastatic GIST who have responsive disease or focal resistance to tyrosine kinase inhibitor therapy may benefit from elective surgical resection. Surgery for patients with metastatic GIST who have multifocal resistance is generally not indicated, and these patients should be considered for clinical trials of new systemic agents.

Imatinib does not induce cardiac left ventricular failure in gastrointestinal stromal tumours patients: Analyis of EORTC-ISG-AGITG study 62005

Recent publications have suggested that imatinib (Glivec) may be cardiotoxic. We have therefore assessed the largest study on the agent performed in patients with gastrointestinal stromal tumours, randomising a daily dose of 400mg versus 800 mg. 946 Patients were entered, 942 patients received at least one dose of imatinib. The median time on treatment was 24 months. A total of 24,574 exposure months could be analysed. We could not identify an excess of cardiac events in the study population. In 2 patients (0.2%) a possible cardiotoxic effect of imatinib could not fully be excluded. The current analysis of a large randomised prospective study could not confirm previous suggestions of imatinib induced cardiac toxicity.

Population pharmacokinetics of imatinib and the role of alpha-acid glycoprotein

AIMS

The aims of this observational study were to assess the variability in imatinib pharmacokinetics and to explore the relationship between its disposition and various biological covariates, especially plasma alpha1-acid glycoprotein concentrations.

METHODS

A population pharmacokinetic analysis was performed using NONMEM based on 321 plasma samples from 59 patients with either chronic myeloid leukaemia or gastrointestinal stromal tumours. The influence of covariates on oral clearance and volume of distribution was examined. Furthermore, the in vivo intracellular pharmacokinetics of imatinib was explored in five patients.

RESULTS

A one-compartment model with first-order absorption appropriately described the data, giving a mean (+/-SEM) oral clearance of 14.3 l h-1 (+/-1.0) and a volume of distribution of 347 l (+/-62). Oral clearance was influenced by body weight, age, sex and disease diagnosis. A large proportion of the interindividual variability (36% of clearance and 63% of volume of distribution) remained unexplained by these demographic covariates. Plasma alpha1-acid glycoprotein concentrations had a marked influence on total imatinib concentrations. Moreover, we observed an intra/extracellular ratio of 8, suggesting substantial uptake of the drug into the target cells.

CONCLUSION

Because of the high pharmacokinetic variability of imatinib and the reported relationships between its plasma concentration and efficacy and toxicity, the usefulness of therapeutic drug monitoring as an aid to optimizing therapy should be further investigated. Ideally, such an approach should take account of either circulating alpha1-acid glycoprotein concentrations or free imatinib concentrations.

Population pharmacokinetics of imatinib and the role of alpha-acid glycoprotein

AIMS

The aims of this observational study were to assess the variability in imatinib pharmacokinetics and to explore the relationship between its disposition and various biological covariates, especially plasma alpha1-acid glycoprotein concentrations.

METHODS

A population pharmacokinetic analysis was performed using NONMEM based on 321 plasma samples from 59 patients with either chronic myeloid leukaemia or gastrointestinal stromal tumours. The influence of covariates on oral clearance and volume of distribution was examined. Furthermore, the in vivo intracellular pharmacokinetics of imatinib was explored in five patients.

RESULTS

A one-compartment model with first-order absorption appropriately described the data, giving a mean (+/-SEM) oral clearance of 14.3 l h-1 (+/-1.0) and a volume of distribution of 347 l (+/-62). Oral clearance was influenced by body weight, age, sex and disease diagnosis. A large proportion of the interindividual variability (36% of clearance and 63% of volume of distribution) remained unexplained by these demographic covariates. Plasma alpha1-acid glycoprotein concentrations had a marked influence on total imatinib concentrations. Moreover, we observed an intra/extracellular ratio of 8, suggesting substantial uptake of the drug into the target cells.

CONCLUSION

Because of the high pharmacokinetic variability of imatinib and the reported relationships between its plasma concentration and efficacy and toxicity, the usefulness of therapeutic drug monitoring as an aid to optimizing therapy should be further investigated. Ideally, such an approach should take account of either circulating alpha1-acid glycoprotein concentrations or free imatinib concentrations.

Emerging drugs for the treatment of soft tissue sarcomas

Soft tissue sarcomas are rare cancers of mesenchymal origin. Recent progress in the understanding of the biology of these rare tumours has enabled the identification of distinct molecular and pathological entities within this heterogenous group of neoplasms, and has paved the way for the development of targeted therapeutics directed against activated kinases. One of the most clear examples is the identification of KIT and platelet-derived growth factor receptor-alpha kinase mutations in gastrointestinal stromal tumours, a subset of sarcomas arising from precursors of the interstitial cells of Cajal in the digestive tract, which led to the development of imatinib, sunitinib and other tyrosine kinase inhibitors for the treatment of solid tumours. This model has become the paradigm of a targeted treatment of solid tumours designed to inhibit the causal alteration in the oncogenesis of these tumours. This review summarises treatment strategies in the context of advanced disease and discusses new compounds being developed for patients with soft tissue sarcomas.

Current issues in gastrointestinal stromal tumors: incidence, molecular biology, and contemporary treatment of localized and advanced disease

PURPOSE OF REVIEW

Few areas in oncology have witnessed the major paradigm shift that has been noted in the understanding and management of gastrointestinal stromal tumors. This review highlights the progress made over the last 2 years.

RECENT FINDINGS

Population-based studies have provided insight into the true incidence of gastrointestinal stromal tumors. Improved understanding of the molecular biology has provided prognostic implications and may guide treatment in the future. More mature follow-up data from phase III trials have proven that the targeted tyrosine kinase inhibitor imatinib mesylate is a dramatically effective agent, but the duration of its benefits are finite, and drug resistance is an increasingly more common phenomenon. Adjuvant and neoadjuvant trials of imatinib are currently underway. A second targeted tyrosine kinase inhibitor, sunitinib malate, has been approved for the treatment of imatinib-resistant gastrointestinal stromal tumors after recent encouraging results. Finally, the success with imatinib and sunitinib has encouraged investigators to reevaluate the role of surgery in advanced gastrointestinal stromal tumors.

SUMMARY

The multidisciplinary management of gastrointestinal stromal tumors serves as a model of how new targeted molecular therapies can be combined with traditional treatment modalities to improve survival in advanced malignancies.

Imatinib

Imatinib (Gleevec, Glivec is a small molecule inhibitor of tyrosine kinase that has been evaluated for efficacy in patients with gastrointestinal stromal tumours (GIST). The drug is approved for the treatment of unresectable and/or metastatic, KIT-positive GIST in the US, Europe and many other countries. Imatinib has had a significant impact on the management of advanced GIST, which has traditionally had a poor prognosis, and has quickly become the first choice of treatment in the medical therapy of unresectable and/or metastatic, KIT-positive GIST. In randomised, nonblind trials, imatinib 400-800 mg/day produced complete or partial responses in up to two-thirds of patients, with long-term efficacy, and substantially prolonged progression-free and overall survival. The drug was generally well tolerated in GIST patients, including during long-term treatment. Imatinib dosages higher than 400 mg/day (up to 800 mg/day) may improve progression-free survival, with an increase in dosage benefiting some patients who show disease progression at the lower dosage, particularly in those with exon 9 mutation; however, there is also a dose-related increase in imatinib toxicity. Mutational genotype and other, non-biomolecular factors may aid in guiding imatinib therapy and predicting prognosis in GIST patients. Further data are required to evaluate the use of imatinib in adjuvant and neoadjuvant settings. Nevertheless, imatinib currently provides the most effective treatment option in the management of advanced GIST.

Kinase inhibitors in the treatment of renal cell carcinoma

Immunotherapy confers a small but significant overall survival advantage in metastatic renal cell carcinoma (RCC) but a need exists to develop more effective systemic therapies. Angiogenesis has a key role in the pathophysiology of renal cell carcinoma and vascular endothelial growth factor (VEGF) is an important mediator of this process. Sunitinib, sorafenib and axitinib are new agents which belong to a class of drugs called kinase inhibitors and inhibit the VEGF, platelet-derived growth factor (PDGF) and c-KIT receptor tyrosine kinases. Temsirolimus inhibits the mammalian target of rapamycin (mTOR). All these agents have shown significant activity with manageable toxicity in metastatic RCC in phase 2 studies in patients generally pretreated with immunotherapy, whilst prolonged progression-free survival in a phase 3 study has been reported with sorafenib in comparison with placebo. Further phase 3 trials are recruiting and the combination of kinase inhibitors with other therapies is under investigation.

Pharmacokinetic-Pharmacodynamic Relationships of Imatinib and Its Main Metabolite in Patients with Advanced Gastrointestinal Stromal Tumors

PURPOSE

This study explored factors affecting the pharmacokinetic variability of imatinib and CGP 74588, and the pharmacokinetic-pharmacodynamic correlations in patients with advanced gastrointestinal stromal tumors.

EXPERIMENTAL DESIGN

Thirty-five patients with advanced gastrointestinal stromal tumors received 400 mg of imatinib daily. Six blood samples were drawn: before intake, during 1- to 3- and 6- to 9-hour intervals after intake on day 1, and before intake on days 2, 30, and 60. Plasma imatinib and CGP 74588 concentrations were quantified by reverse-phase high-performance liquid chromatography coupled with tandem mass spectrometry, and analyzed by the population pharmacokinetic method (NONMEM program). The influence of 17 covariates on imatinib clearance (CL) and CGP 74588 clearance (CLM/fm) was studied. These covariates included clinical and biological variables and occasion (OCC = 0 for pharmacokinetic data corresponding to the first administration, or OCC = 1 for the day 30 or 60 administrations).

RESULTS

The best regression formulas were: CL (L/h) = 7.97 (AAG/1.15)(-0.52), and CLM/fm (L/h) = 58.6 (AAG/1.15)(-0.60) x 0.55(OCC), with the plasma alpha1-acid glycoprotein (AAG) levels indicating that both clearance values decreased at a higher AAG level. A significant time-dependent decrease in CLM/fm was evidenced with a mean (+SD) CGP 74588/imatinib area under the curve (AUC) ratio of 0.25 (+/-0.07) at steady state, compared with 0.14 (+/-0.03) on day 1. Hematologic toxicity was correlated with pharmacokinetic variables: the correlation observed with the estimated unbound imatinib AUC at steady-state (r = 0.56, P < 0.001) was larger than that of the total imatinib AUC (r = 0.32, NS).

CONCLUSIONS

The plasma AAG levels influenced imatinib pharmacokinetics. A protein-binding phenomenon needs to be considered when exploring the correlations between pharmacokinetics and pharmacodynamics.

Efficacy and safety of sunitinib in patients with advanced gastrointestinal stromal tumour after failure of imatinib: a randomised controlled trial

BACKGROUND

No effective therapeutic options for patients with unresectable imatinib-resistant gastrointestinal stromal tumour are available. We did a randomised, double-blind, placebo-controlled, multicentre, international trial to assess tolerability and anticancer efficacy of sunitinib, a multitargeted tyrosine kinase inhibitor, in patients with advanced gastrointestinal stromal tumour who were resistant to or intolerant of previous treatment with imatinib.

METHODS

Blinded sunitinib or placebo was given orally once daily at a 50-mg starting dose in 6-week cycles with 4 weeks on and 2 weeks off treatment. The primary endpoint was time to tumour progression. Intention-to-treat, modified intention-to-treat, and per-protocol analyses were done. This study is registered at ClinicalTrials.gov, number NCT00075218.

FINDINGS

312 patients were randomised in a 2:1 ratio to receive sunitinib (n=207) or placebo (n=105); the trial was unblinded early when a planned interim analysis showed significantly longer time to tumour progression with sunitinib. Median time to tumour progression was 27.3 weeks (95% CI 16.0-32.1) in patients receiving sunitinib and 6.4 weeks (4.4-10.0) in those on placebo (hazard ratio 0.33; p<0.0001). Therapy was reasonably well tolerated; the most common treatment-related adverse events were fatigue, diarrhoea, skin discolouration, and nausea.

INTERPRETATION

We noted significant clinical benefit, including disease control and superior survival, with sunitinib compared with placebo in patients with advanced gastrointestinal stromal tumour after failure and discontinuation of imatinab. Tolerability was acceptable.

[Effectiveness and safety of imatinib in seven gastrointestinal stromal tumor cases]

OBJECTIVE

To measure the effectiveness and safety of imatinib for gstrointestinal stromal tumors (GISTs).

METHOD

A retrospective study from 1993 through June 2005 by identifying all patients diagnosed with GIST by the Pathology Department. The medical records of those treated with imatinib were reviewed. Demographic, diagnostic, therapeutic, and outcome-related data were collected.

RESULTS

Twenty-five patients were identified, 7 of them treated with imatinib. Total responses were 4/7; 2/7 cases were complete responses, and 2/7 were partial responses. Mean actuarial disease-free survival was 10 months, and overall survival was 44 months. Adverse reactions (ARs) reported included: 33% (5) gastrointestinal events, 40% (6) dermatologic events and/or edema, 14% (2) blood toxicity, and 13% (2) asthenia. In all, 2/7 patients experienced no imatinib-related toxicity.

CONCLUSIONS

In our experience, imatinib is an effective, well tolerated therapy for malignant [c-Kit (CD117)-positive], non-resectable and/or metastatic GIST.

Predicting toxicities for patients with advanced gastrointestinal stromal tumours treated with imatinib: A study of the European Organisation for Research and Treatment of Cancer, the Italian Sarcoma Group, and the Australasian Gastro-Intestinal Trials Group (EORTC–ISG–AGITG)

The aim of this study was to identify prognostic factors for toxicity to treatment with imatinib. The study was based on 942 patients with gastrointestinal stromal tumours (GIST) randomised to receive imatinib at different doses. The correlation between toxicities occurring with a Common Toxicity Criteria (CTC) grade 2 or more (non-haematological) or grade 3 or 4 (haematological) and imatinib dose, age, sex, performance status, original disease site, site and size of lesions at trial entry, baseline haematological and biological parameters was investigated. Anaemia was correlated with dose and baseline haemoglobin level, and neutropaenia with baseline neutrophil count and haemoglobin level. The risk of non-haematological toxicities was dose dependent and higher in females (oedema, nausea, diarrhoea), and in patients of advanced age (oedema, rash fatigue), poor performance status (fatigue and nausea), prior chemotherapy (fatigue), tumour of identified gastrointestinal origin (diarrhoea) and small lesions (rash). A multivariate risk calculator that can be used in the clinic for individual patients is proposed.

Gastrointestinal stromal tumours: consensus statement on diagnosis and treatment

In the multidisciplinary management of gastrointestinal stromal tumours (GISTs), there is a need to coordinate the efforts of pathology, radiology, surgery and oncology. Surgery is the mainstay for resectable nonmetastatic GISTs, but virtually all GISTs are associated with a risk of metastasis. Imatinib 400 mg/day with or without surgery is the recommended first-line treatment for recurrent or metastatic GIST; a higher dose may be considered in patients who progress, develop secondary resistance or present with specific genotypic characteristics. Adjuvant or neoadjuvant imatinib is not advised for resectable nonmetastatic GISTs. Neoadjuvant imatinib may be considered when surgery would result in significant morbidity or loss of organ function. Follow-up computed tomography imaging is recommended every three to six months for at least five years. Patients with metastatic disease should be continued on imatinib due to the high risk of recurrence on discontinuation of therapy. Treatment should be continued until there is progression or intolerable adverse effects. If dose escalation with imatinib fails, a clinical trial with novel agents alone or in combination may be considered. The present recommendations were developed at a surgical subcommittee meeting and a subsequent full Advisory Committee meeting held in Toronto, Ontario, in April 2005, under the sponsorship of Novartis Pharmaceuticals Canada Inc.