Update of phase I study of imatinib (STI571) in advanced soft tissue sarcomas and gastrointestinal stromal tumors: a report of the EORTC Soft Tissue and Bone Sarcoma Group

Using body composition to predict treatment-related adverse events and disease-free survival in patients with gastrointestinal stromal tumors treated with imatinib: a retrospective cohort study

Background

Imatinib (IM) is the primary treatment for Gastrointestinal stromal tumor (GIST), but it faces significant challenges with resistance and a high incidence of adverse events. This study aims to assess the predictive value of baseline body composition parameters on treatment-related adverse events and disease-free survival (DFS) in GIST patients treated with imatinib.

Materials and Methods

A single-center retrospective analysis was conducted on 107 moderate or high-risk stratification GIST patients diagnosed from 2014 to 2020 at the First Affiliated Hospital of Nanjing Medical University. Body composition parameters, including skeletal muscle index (SMI), myosteatosis, cachexia index (CXI), and Fat-Free Mass (FFM), etc. were obtained using abdominal CT images and clinical data. Logistic and COX regression models were used to analyze the relationship between these indicators and treatment-related adverse events and DFS.

Results

Multivariate analysis revealed that myosteatosis (OR=7.640, P<0.001) and drug dose (OR=1.349, P=0.010) were independent risk factors for adverse events, while a higher CXI (OR=0.983, P=0.017) was protective. Additionally, LAMA/SMA% (OR=1.072, P=0.028) was identified as an independent risk factor for dose-limiting toxicity (DLT). Independent predictors of DFS included sarcopenia (HR=3.067, P=0.013), myosteatosis (HR=6.985, P=0.024), risk stratification (HR=9.562, high-risk vs. moderate-risk, P=0.003), and C-KIT mutation (HR=3.615, C-KIT exon 9 mutation vs. 11, P=0.013).

Conclusions

Baseline body composition parameters, particularly myosteatosis, effectively predict the adverse events and DFS in patients taking imatinib. Personalized treatment, such as targeted nutritional and exercise interventions, and close monitoring of patients with myosteatosis or sarcopenia can enhance compliance and improve survival rates.

Low-dose Imatinib Efficacy in a Gastrointestinal Stromal Tumor Patient With KIT Exon 11 W557_K558 Deletion

BACKGROUND/AIM

Gastrointestinal stromal tumors (GISTs) are rare cancers originating from Cajal's stromal cells in the gastrointestinal tract. The most common driver mutation in these cancers is the KIT mutation. This report presents a case of response to low-dose imatinib in a patient with GIST harboring KIT exon 11 W557_K558 deletion.

CASE REPORT

In June 2023, an 82-year-old male developed perineal pain. Computed tomography (CT) imaging revealed a mass measuring >9 cm, extending from the rectum to the prostate. Submucosal tumor biopsy revealed a tumor with CD117-positive and DOG1-positive spindle-shaped cells leading to a diagnosis of GIST. c-Kit gene mutation analysis detected a W557_K558 deletion in exon 11. Treatment with imatinib (400 mg/day) was initiated in late October 2023 to preserve organ function; the dose was reduced to 300 mg/day after 5 days of treatment and further reduced to 200 mg/day after 10 days, with continued treatment at this dose. The CT performed in January, April, and June 2024 showed that the rectal GIST had shrunk. The blood imatinib concentration remained at approximately 650 ng/ml from January to March 2024 and decreased to 391 ng/ml in May 2024.

CONCLUSION

The response rate of GISTs to imatinib is influenced by genetic mutations. GIST with KIT exon 11 W557_K558 deletion is associated with a high risk of recurrence. In vitro data showed that low-dose imatinib was effective in such cases. Low-dose imatinib is a treatment option for patients with GIST harboring KIT exon 11 W557_K558 deletion who are intolerant to high-dose imatinib.

The Role of Macrophages in Sarcoma Tumor Microenvironment and Treatment

Sarcomas are a heterogeneous group of malignant mesenchymal tumors, including soft tissue and bone sarcomas. Macrophages in the tumor microenvironment, involved in immunosuppression and leading to tumor development, are called tumor-associated macrophages (TAMs). TAMs are very important in modulating the microenvironment of sarcomas by expressing specific markers and secreting factors that influence immune and tumor cells. They are involved in many signaling pathways, such as p-STAT3/p-Erk1/2, PI3K/Akt, JAK/MAPK, and JAK/STAT3. TAMs also significantly impact the clinical outcomes of patients suffering from sarcomas and are mainly related to poor overall survival rates among bone and soft tissue sarcomas, for example, chondrosarcoma, osteosarcoma, liposarcoma, synovial sarcoma, and undifferentiated pleomorphic sarcoma. This review summarizes the current knowledge on TAMs in sarcomas, focusing on specific markers on sarcoma cells, cell-cell interactions, and the possibly involved molecular pathways. Furthermore, we discuss the clinical significance of macrophages in sarcomas as a potential target for new therapies, presenting clinical relevance, possible new treatment options, and ongoing clinical trials using TAMs in sarcoma treatment.

A systematic review and network meta-analysis of the efficacy and safety of third-line and over third-line therapy after imatinib and TKI resistance in advanced gastrointestinal stromal tumor

Tyrosine kinase inhibitors (TKIs) have greatly improved the prognosis of unresectable and metastatic gastrointestinal stromal tumors (GISTs) in the last two decades. Imatinib and sunitinib are recommended as first-line and second-line therapies, respectively. However, there is a lack of precision therapy for refractory GISTs regarding therapy after imatinib and sunitinib. We comprehensively searched electronic databases, including PubMed, EMBASE, Web of Science, Cochrane Library, and ClinicalTrials, from inception to October 2022. Randomized controlled trials featuring comparisons with third-line or over third-line therapies against GISTs were eligible. The primary outcome was progression-free survival (PFS). All network calculations were performed using random effect models, and the ranking of regimens were numerically based on the surface under the cumulative ranking (SUCRA) statistics. A total of seven studies were eligible for inclusion in this network meta-analysis. After analysis, ripretinib was ranked at the top in progression-free survival (PFS), overall survival (OS), and disease control rate (DCR) (SUCRA statistics: 83.1%, 82.5%, and 86.5%, respectively), whereas nilotinib and pimitespib presented better tolerability (SUCRA statistics: 64.9% and 63.8%, respectively). We found that regorafenib seemed more reliable for clinical administration, and ripretinib showed good effectiveness for the over third-line therapy. Precise targeted therapy is a critical direction for the future treatment of GIST, and more high-quality studies of new agents are expected.

Characteristics of 18F-FDG and 18F-FDOPA PET in an 8-year-old neutered male Yorkshire Terrier dog with glioma: long-term chemotherapy using hydroxyurea plus imatinib with prednisolone and immunoreactivity for PDGFR-β and LAT1

An 8-year-old neutered male Yorkshire Terrier dog presented with head pressing, vestibular ataxia, neck tenderness, and no oculocephalic reflex. A demarcated lesion in the pons was identified on MRI. The patient was tentatively diagnosed with a glioma and was treated with hydroxyurea plus imatinib and prednisolone. After 30 days of therapeutic treatment, the patient showed a clear improvement in neurological signs, which lasted for 1117 days. On day 569 after the initiation of treatment, ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) was performed with no significant findings on visual analysis. The average and maximal standardized uptake values (SUVs) were 1.92 and 2.29, respectively. The tumor-to-normal-tissue (T/N) ratio was 0.97. The first evidence of clinical deterioration was noticed on day 1147. On day 1155, 3,4-dihydroxy-6-[¹⁸F]-fluoro-l-phenylalanine (¹⁸F-FDOPA)-PET was performed. High uptake of ¹⁸F-FDOPA was observed in the intracranial lesion. The mean and maximal SUVs of the tumor were 1.59 and 2.29, respectively. The T/N ratio was 2.22. The patient was euthanized on day 1155 and histopathologic evaluations confirmed glioma (astrocytoma). This case shows that chemotherapy with hydroxyurea plus imatinib may be considered in the treatment of canine glioma. Furthermore, this is the first case describing the application of ¹⁸F-FDG and ¹⁸F-FDOPA in a dog with glioma.

The Impact of Immunological Checkpoint Inhibitors and Targeted Therapy on Chronic Pruritus in Cancer Patients

Although pruritus may sometimes be a consequential situation to neoplasms, it more frequently emerges after commencing chemotherapy. In this review, we present our analysis of the chemotherapy treatments that most often induce skin changes and itching. After discussing conventional chemotherapies capable of inducing pruritus, we present our evaluation of new drugs such as immunological checkpoint inhibitors (ICIs), tyrosine kinase inhibitors, and monoclonal antibodies. Although ICIs and targeted therapy are thought to damage tumor cells, these therapies can modify homeostatic events of the epidermis and dermis, causing the occurrence of cutaneous toxicities in treated subjects. In the face of greater efficacy, greater skin toxicity has been reported for most of these drugs. A remarkable aspect of some reports is the presence of a probable correlation between cutaneous toxicity and treatment effectiveness in tumor patients who were treated with novel drugs such as nivolumab or pembrolizumab. Findings from these experiments demonstrate that the occurrence of any grade of skin side effects can be considered as a predictor of a better outcome. In the near future, studies on the relationship between the onset of skin alterations and outcomes could open new perspectives on the treatment of neoplasms through specific target therapy.

Surgical resection improves overall survival of patients with small bowel leiomyosarcoma

PURPOSE

Small bowel leiomyosarcoma (SB LMS) is a rare disease with few studies characterizing its outcomes. This study aims to evaluate surgical outcomes for patients with SB LMS.

METHODS

The National Cancer Database was queried from 2004 to 2016 to identify patients with SB LMS who underwent surgical resection. The primary outcome was overall survival.

RESULTS

A total of 288 patients with SB LMS who had undergone surgical resection were identified. The median age was 63, and the majority of patients were female (56%), White (82%), and had a Charlson comorbidity score of zero (76%). Eighty-one percent of patients had negative margins following surgical resection. Fourteen percent of patients had metastatic disease at the time of diagnosis. Nineteen percent of patients received chemotherapy and 3% of patients received radiation. One-year overall survival was 77% (95% CI: 72-82%) and 5-year overall survival was 43% (95% CI: 36-49%). Higher grade (HR: 1.98, 95% CI: 1.10-3.55, p = 0.02) and metastatic disease at diagnosis (HR: 2.57, 95% CI: 1.45-4.55, p = 0.001) were independently associated with higher risk of death.

CONCLUSION

SB LMS is a rare disease entity, with treatment centering on complete surgical resection. Our results demonstrate that overall survival is higher than previously thought. Timely diagnosis to allow for complete surgical resection is key, and investigation into the possible role of chemotherapy or radiation therapy is needed.

Pharmacogenetics in the treatment of gastrointestinal stromal tumors - an updated review

INTRODUCTION

Gastrointestinal stromal tumors (GIST) are the best example of a targeted therapy in solid tumors. The introduction of tyrosine kinase inhibitors (TKIs) deeply improved the prognosis of this tumor. However, a degree of inter-patient variability is still reported in response rates and pharmacogenetics may play an important role in the final clinical outcome.

AREAS COVERED

In this review, the authors provide an updated overview of the pharmacogenetic literature analyzing the role of polymorphisms in both GIST treatment efficacy and toxicity.

EXPERT OPINION

Besides the primary role of somatic DNA in dictating the clinical response to TKIs, several polymorphisms influencing their pharmacokinetics and pharmacodynamics have been identified as being potentially involved. In the last 10 years, many potential biomarkers have been proposed to predict clinical response and toxicity after TKI administration. However, the evidence is still too limited to promote a clinical translation. To date, the somatic mutational status represents the main player in clinical response to TKIs in GIST treatment; however, pharmacogenetics could still explain the degree of inter-patient variability observed in GIST patients. A combination of different theoretical approaches, experimental model systems, and statistical methods is clearly needed, in order to translate pharmacogenetics to clinical practice in the near future.

Lack of Prognostic Significance of Connexin-43 Labeling in a Series of 46 Gastrointestinal Stromal Tumors

Background

Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors with variable malignant potential. Connexin-43 (C×43) is the commonest gap-junction protein and has been frequently investigated in oncology. Our aim was to establish the immunohistochemical expression of C×43 in relation to GIST location, size, Ki67 index, tumor grade and follow-up.

Materials and methods

The study included postoperative samples of 46 patients treated for GIST in the 1999–2010 time frame. Complete clinical workup was available for 38 patients (82.6%); total surgical resection was carried out in 32 (84.2%) patients, while 13 (34.2%) patients underwent chemotherapy. Median follow-up was 40.7 months (range, 1-134).

Results

The calculated incidence of GIST in our setting was 11.5 per million. C×43 was expressed in 43/46 (93.5%) GIST cases, with a significant difference between stomach- and small intestine-derived tumors (p=0.006). Ki67 was 10% on average (range, 1–22) and was not correlated with tumor location (p=0.194). C×43 did not show significance with regard to tumor size (p=0.264) or higher tumor grade (p=0.658), as opposed to Ki67, which significantly correlated with both (p=0.0048 and p<0.001, respectively). C×43 and Ki67 were not significantly correlated (p=0.708). Ki67 correlated with time to recurrence (p=0.022). Ki67 >11% was taken as the indication to start imatinib chemotherapy (sensitivity 61.5%, specificity 92.0%, p=0.022). Ten (66.7%) of 15 patients with long-term (>5 years) follow-up were in remission.

Conclusion

C×43 was frequently expressed in GISTs regardless of tumor site. However, no significant relationships to histopathological parameters suggestive for prognosis were found. Further investigations might clarify the roles of C×43 in GIST oncogenesis.

Gastrointestinal Stromal Tumors (GISTs): From Science to Targeted Therapy

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. GISTs represent a distinct category of tumors characterized by oncogenic mutations of the KIT receptor tyrosine kinase in a majority of patients. KIT is useful not only for the diagnosis but also for targeted therapy of this disease. Imatinib, a tyrosine kinase inhibitor, is widely used in advanced and metastatic GISTs. This agent revolutionized the treatment strategy of advanced disease and is being tested in the neoadjuvant and adjuvant settings with encouraging results. New therapeutic agents like sunitinib have now been approved, enriching the treatment scenario for imatinib-resistant GISTs. The present review reports on the peculiar characteristics of this disease through its biology and molecular patterns, focusing on the predictive value of KIT mutations and their correlation with clinical outcome as well as on the activity of and resistance to approved targeted drugs.

Systemic Therapy in Metastatic or Unresectable Well-Differentiated/Dedifferentiated Liposarcoma

Liposarcoma is one of the most common subtypes of soft-tissue sarcoma and consists of three main subtypes, of which well-differentiated liposarcoma and dedifferentiated liposarcoma account for 40–45%. The current mainstay of systemic treatment for patients with metastatic or unresectable disease remains doxorubicin with or without ifosfamide in the first-line setting. Recently, eribulin and trabectedin have been approved by the US Food and Drug Administration for recurrent liposarcomas and progress in molecular characterization of these tumors has opened up new and potential novel treatment targets. This review will focus on the evidence base for current treatment strategies and will also discuss potential future options.

Management of Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors had the reputation for poor outcomes because of their lack of response to nonsurgical interventions. The discovery of gain-of-function mutations involving receptor tyrosine kinase growth factor receptors altered the biological understanding and management. Beginning in 2000, management of these tumors has changed dramatically because of the availability of tyrosine kinase inhibitors. The role of surgery continues to be refined. This article reviews how surgery and systemic therapy are being used, incorporating definitions of risk. Decisions on how to treat a patient is based on the risk of progression, pathologic characteristics, and tumor location.

Possible Role of Interleukin-31/33 Axis in Imatinib Mesylate-Associated Skin Toxicity

Imatinib mesylate is a small-molecule tyrosine kinase inhibitor (TKi) designed to target c-ABL and BCR-ABL, approved for the treatment of chronic myeloid leukemia and gastrointestinal stromal tumors. Adverse cutaneous reactions induced by imatinib are frequent, generally moderate, and dose-dependent. The aim of this work was to investigate the possible contribution of interleukin (IL)-33 and IL-31, cytokines involved in disorders associated with itching, in the pathogenesis of pruritus in a patient undergoing imatinib mesylate treatment. His IL-31 and IL-33 serum levels were significantly higher than in the control group (respectively 96.6 pg/mL vs. 7.623±7.681 pg/mL and 27.566 pg/mL vs. 6.170±7.060 pg/mL). In light of these findings, imatinib mesylate-related symptoms of dermatologic toxicities might be related to the release of IL-31 and IL-33. In particular, it is supposable that TKi usage could cause keratinocyte injury, the release of IL-33, and the consequent interaction with its receptor on mast cells that induces the secretion of several factors capable of causing skin manifestations, including IL-31, a known pruritus-inducing cytokine. This report, to the best of our knowledge, is the first work describing the possible involvement of the IL-31/IL-33 axis in the pathogenesis of skin side effects related to imatinib mesylate treatment.

MicroRNAs and Gastrointestinal Stromal Tumor

Gastrointestinal stromal tumor (GIST) is the most commonly diagnosed mesenchymal tumor in the gastrointestinal tract. This tumor type is driven by gain-of-function mutations in receptor tyrosine kinases (such as KIT, PDGFRA, and BRAF) or loss-of-function mutations in succinate dehydrogenase complex subunit genes (SDHx). Molecular studies on GIST have improved our understanding of the biology of the disease and have led to the use of targeted therapy approach, such as imatinib for KIT/PDGFRA-mutated GIST. Recently, microRNAs have emerged as important regulators of KIT expression, cancer cell behavior, and imatinib response in GIST. This chapter aims to provide an overview on current understanding of the biological roles of microRNAs in GIST and possible implications in prognosis and therapeutic response.

Management of a Gastrobronchial Fistula Connected to the Skin in a Giant Extragastric Stromal Tumor

Introduction. Gastrointestinal stromal tumors first treatment should be surgical resection, but when metastases are diagnosed or the tumor is unresectable, imatinib must be the first option. This treatment could induce some serious complications difficult to resolve. Case Report. We present a 47-year-old black man with a giant unresectable gastric stromal tumor under imatinib therapy who presented serious complications such as massive gastrointestinal bleeding and a gastrobronchial fistula connected with the skin, successfully treated by surgery and gastroscopy. Discussion. Complications due to imatinib therapy can result in life threatening. They represent a challenge for surgeons and digestologists; creative strategies are needed in order to resolve them.

PET/Computed Tomography in the Diagnosis and Staging of Gastric Cancers

Although there has been a reduction of the incidence and mortality of gastric cancer, it remains among the commonest causes of cancer-related death. Accurate staging and evaluation of treatment response are vital for management. PET is used to complement anatomic imaging in cancer management. PET/computed tomography (CT) has demonstrated its potential value for preoperative staging, evaluation of response to therapy, and detection of recurrence. Not all types of gastric cancers have a high affinity for fluorodeoxyglucose. PET/CT in the evaluation and staging of gastric cancer is not established, but studies indicate that there may be an evolving role for this imaging modality.

The DREAM complex in antitumor activity of imatinib mesylate in gastrointestinal stromal tumors

PURPOSE OF REVIEW

Although most gastrointestinal stromal tumors respond well to treatment with the small molecule kinase inhibitor imatinib mesylate (Gleevec), complete remissions are rare and the majority of patients achieve disease stabilization. Furthermore, discontinuation of treatment in the presence of residual tumor mass almost inevitably leads to tumor progression. These observations suggest that a subset of tumor cells not only persists under imatinib treatment, but remains viable. The current article reviews the molecular basis for these findings and explores strategies to exploit them therapeutically.

RECENT FINDINGS

Although imatinib induces apoptosis in a subset of gastrointestinal stromal tumor cells, it leads to a reversible exit from the cell division cycle and entry into G0, a cell cycle state called quiescence, in the remaining cells. Mechanistically, this process involves the DREAM complex (DP, p130/RBL2, E2F4 and MuvB), a newly identified key regulator of quiescence. Interfering with DREAM complex formation either by siRNA-mediated knockdown or by pharmacological inhibition of the regulatory kinase dual-specificity tyrosine phosphorylation-regulated kinase 1A was shown to enhance imatinib-induced gastrointestinal stromal tumor cell death.

SUMMARY

Targeting the DREAM complex and imatinib-induced quiescence could provide opportunities for future therapeutic interventions toward more efficient imatinib responses.

The GIST of targeted therapy for malignant melanoma

The high response rates to the tyrosine kinase inhibitor imatinib in KIT-mutated gastrointestinal stromal tumors (GIST) has led to a paradigm shift in cancer treatment. In a parallel fashion, the field of melanoma is shifting with the utilization of targeted therapy to treat BRAF-mutated melanoma. We reviewed published literature in PubMed on GIST and melanoma, with a focus on both past and current clinical trials. The data presented centers on imatinib, vemurafenib, and most recently dabrafenib, targeting KIT and BRAF mutations and their outcomes in GIST and melanoma. The BRAF(V600E) melanoma mutation, like the KIT exon 11 mutation in GIST, has the highest response to therapy. High response rates with inhibition of KIT in GIST have not been recapitulated in KIT-mutated melanoma. Median time to resistance to targeted agents occurs in ~7 months with BRAF inhibitors and 2 years for imatinib in GIST. In GIST, the development of secondary mutations leads to resistance; however, there have been no similar gatekeeper mutations found in melanoma. Although surgery remains an important component of the treatment of early GIST and melanoma, surgeons will need to continue to define the thresholds and timing for operation in the setting of metastatic disease with improved targeted therapies. Combination treatment strategies may result in more successful clinical outcomes in the management of melanoma in the future.

Genetics and genomics of melanoma

The rapidly increasing incidence of melanoma, coupled with its highly aggressive metastatic nature, is of urgent concern. In order to design rational therapies, it is of critical importance to identify the genetic determinants that drive melanoma formation and progression. To date, signaling cascades emanating from the EGF receptor, c-MET and other receptors are known to be altered in melanoma. Important mutations in signaling molecules, such as BRAF and N-RAS, have been identified. In this review, some of the major genetic alterations and signaling pathways involved in melanoma will be discussed. Given the great deal of genetic heterogeneity observed in melanoma, it is likely that many more genetic determinants exist. Through the use of powerful genomic technologies, it is now possible to identify these additional genetic alterations in melanoma. A critical step in this analysis will be culling bystanders from functionally important drivers, as this will highlight genetic elements that will be promising therapeutic targets. Such technologies and the important points to consider in understanding the genetics of melanoma will be reviewed.

Some Lessons Learned from Imatinib Mesylate Clinical Development in Gastrointestinal Stromal Tumors

Imatinib mesylate is a molecular-targeted agent, shown to be effective in chronic myeloid leukemia and gastrointestinal stromal tumors (GIST). The latter may currently serve as a model on which speculating how the future of molecular-targeted therapy in solid tumors will be. So far, some lessons have been learnt. 1) Molecular-targeted therapy can be effective in the advanced disease setting, resulting in major tumor responses. 2) Patterns of tumor responses may be peculiar, radiologically and pathologically. 3) Anti-tumor activity may be highly predictable by assessing tumor molecular biology. 4) The methodology of clinical development of molecular-targeted agents may differ from standard chemotherapy in some respects, because, say, the preclinical rationale may be stronger, thus increasing the Bayesian prior probability of efficacy, or the optimal dose cannot be determined separately from the assessment of activity and efficacy. 5) Molecular-targeted agents will hardly remain "orphan drugs", if effective. 6) While an obvious impact on survival in the advanced disease setting has been clearly demonstrated, the biologic and clinical impact of molecular-targeted therapy still needs to be elucidated. Its eradicating capabilities, as well as the implications of secondary resistance, are to be understood. 7) Integrated, multimodality approaches, including surgery, may still be of value in the molecular-targeted therapy era.

Gastrointestinal stromal tumors: management of metastatic disease and emerging therapies

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors of the gastrointestinal tract. Before the advent of tyrosine kinase inhibitors (TKIs) there were few treatment options available to patients with metastatic GIST. Surgery was the mainstay of treatment and the prognosis was dismal. With the advent of imatinib and second-line TKIs the prognosis of metastatic GIST has improved dramatically; however, there is still a need for therapies for patients with disease refractory to TKI therapy. Newer agents are under investigation and may have promise. This article discusses the current standard of care in terms of standard and investigational pharmacotherapy in the management of metastatic GIST.

Analysis of activated platelet-derived growth factor β receptor and Ras-MAP kinase pathway in equine sarcoid fibroblasts

Equine sarcoids are skin tumours of fibroblastic origin affecting equids worldwide. Bovine papillomavirus type-1 (BPV-1) and, less commonly, type-2 are recognized as etiological factors of sarcoids. The transforming activity of BPV is related to the functions of its major oncoprotein E5 which binds to the platelet-derived growth factor β receptor (PDGFβR) causing its phosphorylation and activation. In this study, we demonstrate, by coimmunoprecipitation and immunoblotting, that in equine sarcoid derived cell lines PDGFβR is phosphorylated and binds downstream molecules related to Ras-mitogen-activated protein kinase-ERK pathway thus resulting in Ras activation. Imatinib mesylate is a tyrosine kinase receptors inhibitor which selectively inhibits the activation of PDGFβR in the treatment of several human and animal cancers. Here we show that imatinib inhibits receptor phosphorylation, and cell viability assays demonstrate that this drug decreases sarcoid fibroblasts viability in a dose-dependent manner. This study contributes to a better understanding of the molecular mechanisms involved in the pathology of sarcoids and paves the way to a new therapeutic approach for the treatment of this common equine skin neoplasm.

Tyrosine kinase inhibitors (TKIs) in human and pet tumours with special reference to breast cancer: a comparative review

Tyrosine kinase receptors (TKRs) play a key role in tumour cell proliferation and survival since they are involved in endothelial cell activation leading to tumour neoangiogenesis. In particular, vascular endothelial growth factor receptors (VEGFRs), platelet-derived growth factor receptor (PDGFR), stem cell factor receptor (c-KitR), and colony-stimulating factor 1 (CSF-1) are overexpressed or constitutively activated in human and pet malignancies. A variety of small molecule inhibitors targeting specific tyrosine kinases (known as tyrosine kinase inhibitors or TKIs) have recently been approved, or are under investigation, for the treatment of human cancer. TKI application in animal cancer is however relatively recent. This review aims to illustrate the major aspects of tyrosine kinase dysfunctions, with special regard to human and animal cancer of the mammary gland, providing an update on the background of the anti-angiogenic and anti-neoplastic properties of TKIs in human and veterinary cancer.

Treatment response monitoring in patients with gastrointestinal stromal tumor using diffusion-weighted imaging: preliminary results in comparison with positron emission tomography/computed tomography

We compared the parameters derived from diffusion-weighted imaging (DWI) and positron emission tomography/computed tomography (PET/CT) for treatment response evaluation and response prediction in patients with gastrointestinal stromal tumor (GIST). Seven patients with histologically proven metastatic disease were enrolled. DWI and PET/CT data were collected from all patients at diagnosis and from six at follow-up. All 37 lesions were identifiable in DWI with a sensitivity of 100%. To achieve higher accuracy, we used the apparent diffusion coefficient (ADC) of liver and background noise as thresholds for the measurement of the ADCs of lesions. Significant inverse correlations were found between ADC(mean_thr) (ADC(mean) with thresholds) and SUV(mean) (mean standardized uptake value) (R(2)=0.523, p<0.001 at diagnosis, and R(2)=0.916, p<0.001 at follow-up), between ADC(mean_thr) and SUV(max) (maximum SUV) (R(2)=0.529, p<0.001 at diagnosis, and R(2)=0.761, p<0.001 at follow-up), between ΔADC(mean_thr) (percentage change in ADC(mean_thr) ) and ΔSUV(mean) (percentage change in SUV(mean) ) (R(2)=0.384, p<0.001), and between ΔADC(mean_thr) and ΔSUV(max) (percentage change in SUV(max) ) (R(2)=0.500, p<0.001). In lesion-based analysis, pre-treatment ADC(mean_thr) outperformed SUV(mean) and SUV(max) in treatment response prediction, with an area under the receiver operating characteristic curve of 0.706. These results show that DWI can provide a quantitative assessment comparable with PET/CT in GIST lesion characterization, treatment response evaluation and response prediction.

New systemic therapy options for advanced sarcomas

The outcome of patients with advanced soft tissue sarcomas (STS) has not improved much during the last decade. Apart from non-pleomorphic rhabdomyosarcoma, adjuvant chemotherapy has no standard role in high risk STS. In metastatic disease little progress has been made, but during recent years much effort has been put into the development of better clinical study protocols, with stratification of patients to at least the most common histological subtypes, preventing the dilution of potential treatment efficacy when measuring results over the total heterogeneous group of STS. The outcome of patients with advanced STS is however not only dependent on the introduction of new drugs, but also on the availability of dedicated sarcoma centers in which multidisciplinary teams with the input of all experts from different disciplines, such as pathology, radiology, nuclear medicine, surgery, orthopedics radiotherapy and medical oncology is present. Long delay, wrong histological diagnoses, under- and overtreatment are not in the favor of these patients, neither with regard to outcome, nor with respect to short- and long-term toxicity. Disappointedly, centralization is not a routine part of daily care of STS patients and their care givers. Patient advocacy groups are more and more aware of the relevance of treatment in centers of expertise and are active in guiding the patients to these hospitals. At the same time the sarcoma centers should be pro-active in putting patients into clinical trials, also for rare indications within the STS group, as only in this way a better outcome for this group of patients can be reached.

Prolonged Therapy with Imatinib Mesylate before Surgery for Advanced Gastrointestinal Stromal Tumor Results of a Phase II Trial

Purpose. Proven efficacy of imatinib mesylate in gastrointestinal stromal tumour (GIST) has led to its use in advanced disease and, more recently, in adjuvant and neoadjuvant settings. The purpose of this study was to evaluate the optimal neoadjuvant imatinib duration to reduce the morbidity of surgery and increase the possibility of resection completeness in advanced tumours. Patients and Method. Patients with advanced GIST were enrolled into a registered open-label multicenter trial and received imatinib daily for a maximum of 12 months, followed by en bloc resection. Data were prospectively collected regarding tumour assessment, response rate, surgical characteristics, recurrence, and survival. Results. Fourteen patients with advanced GIST were enrolled. According to RECIST criteria, 6 patients had partial response and 8 had stable disease. The overall tumour size reduction was 25% (0–62.5%), and there was no tumour progression. Eleven patients underwent tumour resection, and all had R0 resection. After a median followup of 48 months, 4-year OS and DFS were 100% and 64%, respectively. Conclusion. This prospective trial showed that one year of neoadjuvant imatinib in advanced GIST is safe and associated with high rate of complete microscopic resection. It is not associated with increased resistance, progression, or complication rates.

Current and emerging strategies for the management of imatinib-refractory advanced gastrointestinal stromal tumors

Since its approval by the US Food and Drug Administration in February 2002, the tyrosine kinase inhibitor, imatinib, has become the standard of care for patients with metastatic or unresectable KIT-positive gastrointestinal stromal tumors (GISTs). Imatinib functions by blocking the adenosine triphosphate binding site of the constitutively activated mutant KIT or platelet-derived growth factor receptor α, effectively shutting down the oncogenic signal that drives up to 90% of these tumors. In doing so, it has transformed the management of a condition previously refractory to systemic treatments and established GIST as a model for the use of targeted therapies and oncogene addiction in solid tumors. However, while more than 80% of patients will receive clinical benefit from imatinib monotherapy, more than half will develop progressive disease by 2 years. In this article we review the mechanism and patterns of imatinib resistance in GIST; attempt to offer a practical schema for managing imatinib-refractory patients; and lastly, offer some insight as to future directions and emerging therapeutics for the management of this highly interesting and challenging disease.

Gastrointestinal stromal tumour presenting as gastroduodenal intussusception

Gastroduodenal intussusception secondary to gastrointestinal stromal tumour is a very rare cause for intestinal obstruction. The diagnosis of this condition can be challenging, as symptoms are often non-specific and intermittent. This article reports a case where the diagnosis was made preoperatively with abdominal imaging and was treated by a combination of endoscopic reduction and laparoscopic resection.

A long-term prospective population pharmacokinetic study on imatinib plasma concentrations in GIST patients

PURPOSE

Imatinib minimal (trough) plasma concentrations after one month of treatment have shown a significant association with clinical benefit in patients with gastrointestinal stromal tumors (GIST). Considering that a retrospective pharmacokinetic analysis has also suggested that imatinib clearance increases over time in patients with soft tissue sarcoma and GIST, the primary aim of this study was to assess systemic exposure to imatinib at multiple time points in a long-term prospective population pharmacokinetic study. As imatinib is mainly metabolized in the liver, our secondary aim was to elucidate the potential effects of the volume of liver metastases on exposure to imatinib.

EXPERIMENTAL DESIGN

Full pharmacokinetic blood sampling was conducted in 50 patients with GIST on the first day of imatinib treatment, and after one, six, and 12 months. In addition, on day 14, and monthly during imatinib treatment, trough samples were taken. Pharmacokinetic analysis was conducted using a compartmental model. Volume of liver metastases was assessed by computed tomographic (CT) imaging.

RESULTS

After 90 days of treatment, a significant decrease in imatinib systemic exposure of 29.3% compared with baseline was observed (P < 0.01). For every 100 cm(3) increase of metastatic volume, a predicted decrease of 3.8% in imatinib clearance was observed.

CONCLUSIONS

This is the first prospective pharmacokinetic study in patients with GIST, showing a significant decrease of approximately 30% in imatinib exposure after long-term treatment. This means that future "trough level - clinical benefit" analyses should be time point specific. GIST liver involvement, however, has a marginal effect on imatinib clearance.

Outcome of patients with platelet-derived growth factor receptor alpha-mutated gastrointestinal stromal tumors in the tyrosine kinase inhibitor era

PURPOSE

Platelet-derived growth factor receptor-alpha (PDGFRA) mutations are found in approximately 5% to 7% of advanced gastrointestinal stromal tumors (GIST). We sought to extensively assess the activity of imatinib in this subgroup.

EXPERIMENTAL DESIGN

We conducted an international survey among GIST referral centers to collect clinical data on patients with advanced PDGFRA-mutant GISTs treated with imatinib for advanced disease.

RESULTS

Fifty-eight patients were included, 34 were male (59%), and median age at treatment initiation was 61 (range, 19-83) years. The primary tumor was gastric in 40 cases (69%). Thirty-two patients (55%) had PDGFRA-D842V substitutions whereas 17 (29%) had mutations affecting other codons of exon 18, and nine patients (16%) had mutation in other exons. Fifty-seven patients were evaluable for response, two (4%) had a complete response, eight (14%) had a partial response, and 23 (40%) had stable disease. None of 31 evaluable patients with D842V substitution had a response, whereas 21 of 31 (68%) had progression as their best response. Median progression-free survival was 2.8 [95% confidence interval (CI), 2.6-3.2] months for patients with D842V substitution and 28.5 months (95% CI, 5.4-51.6) for patients with other PDGFRA mutations. With 46 months of follow-up, median overall survival was 14.7 months for patients with D842V substitutions and was not reached for patients with non-D842V mutations.

CONCLUSIONS

This study is the largest reported to date on patients with advanced PDGFRA-mutant GISTs treated with imatinib. Our data confirm that imatinib has little efficacy in the subgroup of patients with D842V substitution in exon 18, whereas other mutations appear to be sensitive to imatinib.

Activity and side effects of imatinib in patients with gastrointestinal stromal tumors: data from a German multicenter trial

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.

Treatment of gastrointestinal stromal tumor: focus on imatinib mesylate

Gastrointestinal stromal tumor (GIST) is a rare primary neoplasm of the gastrointestinal tract, mesentery, or omentum. In the past, surgery has been the only effective treatment. The diagnosis and treatment of GIST has been revolutionized over the past decade, since expression of the receptor tyrosine kinase KIT was shown to occur on these tumors. Mutations in this proto-oncogene commonly cause constitutive activation of the KIT tyrosine kinase receptor, an important factor in the pathogenesis of the disease. The development of specific tyrosine kinase inhibitors, such as imatinib mesylate, has led to a breakthrough in the treatment of advanced GIST. Treatment with this drug has led to significant improvements in survival, with overall response rates in excess of 80%. Side effects are common, but usually manageable. The success of this drug has led to further trials investigating its use in the pre- and postoperative situation. This review summarizes the current knowledge of GIST and imatinib treatment and possible future developments.

Current and emerging pharmacological treatments for gastrointestinal stromal tumour

Gastrointestinal stromal tumours (GIST) are the most common mesenchymal tumours of the gastrointestinal tract, previously classified as leiomyosarcomas. Most GIST express KIT and the majority have mutations in the KIT gene. The most common KIT mutation occurs in the juxtamembrane domain of exon 11. These mutations lead to cellular proliferation and survival. GIST with exon 11 mutations respond better to tyrosine kinase inhibitors (TKIs) than those with exon 9 mutations. Most KIT-negative GIST express platelet-derived growth factor receptor (PDGFR)-α; however, a small percentage of GIST are negative for both KIT and PDGFRα. Imatinib and other TKIs have dramatically improved the outcome of patients with metastatic GIST. Newer and more advanced TKIs are under intense investigation as eventually all GIST patients develop resistant tumours. In addition, these drugs can be utilized in the preoperative setting for patients with unresectable localized tumours or those at high risk for surgical morbidity. TKIs have been given in the adjuvant setting for patients with resected tumours at high risk for recurrence. The duration of adjuvant therapy is currently under evaluation; however, it is possible that these patients would need to continue therapy indefinitely.

Colorectal gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal neoplasm arising in the digestive tract, with an estimated prevalence of 15-20 per 1,000,000. GISTs are related to the interstitial cells of Cajal and are characterized by constitutive over-expression of the transmembrane tyrosine kinase receptor KIT. This is produced by a patognomonic mutation of the proto-oncogene c-kit that occurs in up to 90% of cases. Exon 11 is affected most frequently; exons 9 and 13 are less commonly involved. One-third of GISTs lacking KIT mutations exhibits alternative activating mutations in the PDGFRα gene. Colorectal GISTs represent about 5-10% of the cases, mainly located in the rectum that is the third common site. Benign GISTs are more common, but many tumors are of uncertain malignant potential; tumor size and rate of mitosis are still the most reliable criteria for assessing the risk of an aggressive behavior. Surgery is the first-line treatment for resectable non-metastatic colorectal GIST. Standard oncologic resection is inappropriate because skip metastases and lymphatic spread are rarely reported. Segmental colectomy with negative margins is recommended, and local excision is oncologically adequate in highly selected rectal tumors. Radical surgery alone is not always curative especially in high-risk GISTs, and half of patients develops local recurrences or distant metastases after R0 operation. Medical therapeutic strategies have rapidly evolved after the introduction of targeted molecular therapy. Efficacy and safety of imatinib mesylate was first demonstrated in patients with metastatic and unresectable disease. Adjuvant and neoadjuvant use of imatinib are promising therapeutic options to improve the outcome of surgery to downstage unresectable lesions and to allow less extensive resections.

Molecular basis for primary and secondary tyrosine kinase inhibitor resistance in gastrointestinal stromal tumor

Small molecule kinase inhibitors have irrevocably altered cancer treatment. March 2010 marks the 10th anniversary of using imatinib in gastrointestinal stromal tumors (GIST), a cardinal example of the utility of such targeted therapy in a solid tumor. Before imatinib, metastatic GIST was frustrating to treat due to its resistance to standard cytotoxic chemotherapy. Median survival for patients with metastatic GIST improved from 19 to 60 months with imatinib. In treating patients with GIST, two patterns of tyrosine kinase inhibitor resistance have been observed. In the first, ~9-14% of patients have progression within 3 months of starting imatinib. These patients are classified as having primary or early resistance. Median progression-free survival (PFS) on imatinib is approximately 24 months; patients with later progression are classified as having secondary or acquired resistance. Primary studies and a meta-analysis of studies of imatinib in GIST patients have identified prognostic features that contribute to treatment failure. One of the strongest predictors for success of therapy is KIT or PDGFRA mutational status. Patients with KIT exon 11 mutant GIST have better response rates, PFS, and overall survival compared to other mutations. A great deal has been learned in the last decade about sensitivity and resistance of GIST to imatinib; however, many unanswered questions remain about secondary resistance mechanisms and clinical management in the third- and fourth-line setting. This review will discuss the role of dose effects, and early and late resistance to imatinib and their clinical implications. Patients intolerant to imatinib (5%) and those who progress on imatinib are treated with sunitinib. The mechanism of resistance to sunitinib is unknown at this time but is also appears related to growth of clones with secondary mutations in KIT. Third- and fourth-line treatments of GIST and with future treatment strategies are also discussed.

All-trans retinoic acid inhibits KIT activity and induces apoptosis in gastrointestinal stromal tumor GIST-T1 cell line by affecting on the expression of survivin and Bax protein

BACKGROUND

Imatinib, a selective tyrosine kinase inhibitor, has been used as a standard first-line therapy for irresectable and metastasized gastrointestinal stromal tumor (GIST) patients. Unfortunately, most patients responding to imatinib will eventually exhibit imatinib-resistance, the cause of which is not fully understood. The serious clinical problem of imatinib-resistance demands alternative therapeutic strategy. This study was conducted to investigate the effect of all-trans retinoic acid (ATRA) on GIST cell lines.

METHODS

Cell proliferation was determined by trypan blue dye exclusion test. Western blot analysis was performed to test the expression of activated KIT, its downstream proteins, and apoptosis associated proteins. The cytotoxic interactions of imatinib with ATRA were evaluated using the isobologram of Steel and Peckham.

RESULTS AND CONCLUSION

In this work, for the first time we have demonstrated that ATRA affected on cell proliferation of GIST-T1 and GIST-882 cell line through inhibition of cell growth in a dose dependent manner and induced apoptosis. High dose of ATRA induced morphologic change in GIST-T1 cells, rounded-up cells, and activated the caspase-3 protein. In further examination, we found that the ATRA-induced apoptosis in GIST-T1 cells was accompanied by the down-regulated expression of survivin and up-regulated expression of Bax protein. Moreover, ATRA suppressed the activity of KIT protein in GIST-T1 cells and its downstream signal, AKT activity, but not MAPK activity. We also have demonstrated that combination of ATRA with imatinib showed additive effect by isobologram, suggesting that the combination of ATRA and imatinib may be a novel potential therapeutic option for GIST treatment. Furthermore, the scracht assay result suggested that ATRA was a potential reagent to prevent the invasion or metastasis of GIST cells.

Platelet-derived growth factor receptor beta inhibition increases tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) sensitivity: imatinib and TRAIL dual therapy

BACKGROUND

There is a crucial need for better therapeutic approaches for the treatment of Ewing sarcoma (EWS). Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in EWS cells in vitro. However, in vivo, acquired resistance to TRAIL is a major limiting factor. Platelet-derived growth factor receptor-beta (PDGFR-beta) is highly expressed on EWS cells. Thus, the authors evaluated whether PDGFR-beta blockade could sensitize EWS cells to TRAIL-induced apoptosis in vitro and in vivo.

METHODS

The effect of combined imatinib mesylate (Gleevec) and TRAIL on EWS cell growth and apoptosis was tested in vitro. Stable PDGFR-beta knockdown in EWS cells was achieved by short-hairpin RNA transduction, and TRAIL sensitivity of these cells was measured. Expression of death receptors was measured by fluorescence-activated cell-sorting (FACS) analysis, and caspase 8 activity was evaluated by Western blot analysis. An orthotopic human xenograft model of EWS growth and spontaneous metastasis in nude mice was used to assess the in vivo affect of combined imatinib mesylate and TRAIL.

RESULTS

Imatinib mesylate induced a significant TRAIL proapoptotic effect in EWS cells in vitro. Specific PDGFR-beta silencing in EWS cells enhanced the effects of TRAIL, possibly through an increase in the expression of death receptors 4 and 5. The combination of imatinib mesylate and TRAIL significantly inhibited the growth of primary tumors and decreased the incidence of spontaneous EWS pulmonary metastasis compared with either drug alone.

CONCLUSIONS

PDGFR-beta blockade combined with TRAIL resulted in antihuman EWS activity in vitro and in vivo, suggesting the possibility that combining these treatments will improve anti-EWS therapy.

Neoadjuvant and adjuvant imatinib treatment in gastrointestinal stromal tumor: current status and recent developments

PURPOSE OF REVIEW

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract and is a paradigm of targeted therapy for solid tumors. Elucidation of the biology of GIST enabled use of imatinib, which revolutionized the prognosis of advanced GIST. Whereas surgical resection continues to be the standard of care for primary GIST, judicious and individualized use of adjuvant and neoadjuvant imatinib may enhance the potential for cure in select patients.

RECENT FINDINGS

Prospective trials utilizing adjuvant and neoadjuvant imatinib have established the safety and efficacy of these modalities adjunct to surgical resection. Correlative tissue studies derived from these trials have examined gene expression patterns, metabolic and radiographic response, and apoptosis during the first few days of imatinib therapy. As appropriate use of adjuvant and neoadjuvant imatinib requires proper patient selection, development of a predictive nomogram, and advances in mutational analysis represent progress toward individualized care.

SUMMARY

Imatinib is well tolerated and beneficial as adjuvant and neoadjuvant therapy, but its utility in these settings continues to be refined. The greatest benefit will derive from an individualized approach that considers multiple patient, drug, and tumor characteristics to assess risk and likelihood of benefit for each patient.

Dramatic regression and bleeding of a duodenal GIST during preoperative imatinib therapy: case report and review

Background

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the digestive tract. The majority of GISTs is located in the stomach. Only 3-5% of GISTs are located in the duodenum associated with an increased risk of gastrointestinal bleeding as primary manifestation. With response rates of up to 90%, but complications like bleeding due to tumor necrosis in 3%, imatinib mesylate dramatically altered the pre- and postoperative therapy for GIST patients.

Case presentation

A 58-year-old female patient presented with acute upper gastrointestinal bleeding 2 weeks after a giant GIST of the duodenum had been diagnosed. Neoadjuvant imatinib therapy had been initiated to achieve a tumor downsizing prior to surgery. During emergency laparotomy a partial duodenopancreatectomy was performed to achieve a complete resection of the mass. Histology revealed a high-malignancy GIST infiltrating the duodenal wall. Adjuvant imatinib therapy was initiated. At follow-up (19 months) the patient is still alive and healthy.

Conclusion

Giant GISTs of the duodenum are rare and - in contrast to other localizations - harbour a higher risk of serious bleeding as primary manifestation. Tumor necrosis and tumor bleeding are rare but typical adverse effects of imatinib therapy especially during treatment of high-malignancy GIST. In GIST patients with increased risk of tumor bleeding neoadjuvant imatinib therapy should thoroughly be performed during hospitalization. In cases of duodenal GIST primary surgery should be considered as treatment alternative.

Gastrointestinal Stromal Tumors: A Guide to the Diagnosis

Gastrointestinal stromal tumors (GISTs) have emerged from being a poorly understood and therapeutically refractory sarcoma to a tumor whose biology has not only provided insight into a mechanism of oncogenesis but has also led to a rational basis for therapy. Most GISTs are characterized by KIT protein (CD117) expression and constitutive activating mutations in either the c-kit or platelet-derived growth factor receptor α genes. This information can now be obtained from routine formalin-fixed and paraffin-embedded tissue. Because the correct diagnosis is the key to successful treatment of this tumor, it is incumbent on the pathologist to be familiar with the various gross and histologic patterns shown by these tumors. GISTs range from small incidental stromal nodules to large cystic and solid tumor masses. GISTs show a variety of microscopic patterns and therefore several other tumors enter the differential diagnosis. Fortunately, with an understanding of GIST histology, and with the proper use of immunohistochemistry and molecular analysis, a correct diagnosis can usually be made. In addition to the correct diagnosis, several key attributes of the tumor need to be determined because they provide the basis for proper clinical management. This article summarizes the gross, microscopic, and molecular findings of GISTs, and discusses the differential diagnosis and key attributes of this interesting group of neoplasms.

Practical management of tyrosine kinase inhibitor-associated side effects in GIST

Patients diagnosed with advanced gastrointestinal stromal tumor (GIST) are currently treated with oral tyrosine kinase inhibitors (TKIs). Imatinib mesylate is the standard first-line treatment, and sunitinib malate is administered second-line for patients who are intolerant or progress on imatinib. Imatinib has recently been approved for adjuvant treatment of GIST patients who have a significant risk for relapse. In both the metastatic and adjuvant settings, patients may be on these TKIs for many years. Low plasma imatinib levels have been reported to be associated with a short median time to progression of advanced GIST, stressing the importance of maintaining optimal drug levels. We summarize management of the most frequent and clinically significant adverse effects of imatinib and sunitinib in the treatment of GIST in the context of current guidelines, published literature, and the experience of three large GIST referral centers. The adverse events reviewed include nausea and vomiting, diarrhea, skin rash, musculoskeletal complaints, fatigue, hemorrhage, edema, hand-foot skin reaction, skin and hair discoloration, mucositis, hypertension, cardiac toxicity, hypothyroidism, liver transaminase changes, and hematological toxicity of imatinib and sunitinib. Potential drug-drug interactions with each respective agent are also discussed. With prudent use of supportive care measures, many side effects can be managed without dose reduction or interruption of treatment. On the other hand, individualized tailoring of the dose is often required to manage severe toxicity, such as painful hand-foot skin reactions, fatigue, hepatotoxicity, or cardiac toxicity. Management of many TKI-related adverse effects require further evaluation in prospective clinical trials.

Targeted therapy for gastrointestinal stromal tumors: current status and future perspectives

Gastrointestinal stromal tumors (GISTs) present 80% of gastrointestinal tract mesenchymal tumors, with systemic chemotherapy and radiotherapy being unable to improve survival of patients with advanced disease. The identification of activating mutations in either KIT cell surface growth factor receptor or platelet-derived growth factor receptor alpha, which lead to ligand-independent signal transduction, paved the way for the development of novel agents that selectively inhibit key molecular events in disease pathogenesis. The development of imatinib mesylate in the treatment of metastatic GIST represents a therapeutic breakthrough in molecularly targeted strategies, which crucially improved patients' prognosis while its usefulness in adjuvant and neoadjuvant setting is under study. Sunitinib malate is available in the second-line setting, with ongoing studies evaluating its role in an earlier disease stage, while other targets are under intense investigation in order to enrich the therapeutical armamentarium for this disease. GIST phenotype seems to be an essential indicator of treatment response; thus, obtaining genotype information of each patient may be critical in order to tailor individualized treatment strategies and achieve maximal therapeutic results.