Gastrointestinal stromal tumor: new nodule-within-a-mass pattern of recurrence after partial response to imatinib mesylate

Gastrointestinal stromal tumour (GIST): British Sarcoma Group clinical practice guidelines

BACKGROUND

British Sarcoma Group guidelines for the management of GIST were initially informed by those published by the European Society of Clinical Oncology. This update was written by a group of experts to includes a discussion of the highlight improvements in our knowledge of the disease and recent treatment developments. The guidelines include sections on Incidence, Aetiology, Diagnosis, including risk assessment, Treatment and Follow-up.

METHODS

A careful review of the literature was performed to ensure that wherever possible recommendations are supported by the results of clinical trials or substantive retrospective reports. Areas of uncertainty are indicated appropriately.

CONCLUSION

Guidelines represent a consensus view of current best clinical practice. Where appropriate, key recommendations are given and the levels of evidence and strength of recommendation gradings are those used by the European Society for Medical Oncology (ESMO).

Sarco/endoplasmic reticulum calcium ATPase 3 (SERCA3) expression in gastrointestinal stromal tumours

Accurate characterisation of gastrointestinal stromal tumours (GIST) is important for prognosis and the choice of targeted therapies. Histologically the diagnosis relies on positive immunostaining of tumours for KIT (CD117) and DOG1. Here we report that GISTs also abundantly express the type 3 Sarco/Endoplasmic Reticulum Calcium ATPase (SERCA3). SERCA enzymes transport calcium ions from the cytosol into the endoplasmic reticulum and play an important role in regulating the intensity and the periodicity of calcium-induced cell activation. GISTs from various localisations, histological and molecular subtypes or risk categories were intensely immunopositive for SERCA3 with the exception of PDGFRA-mutated cases where expression was high or moderate. Strong SERCA3 expression was observed also in normal and hyperplastic interstitial cells of Cajal. Decreased SERCA3 expression in GIST was exceptionally observed in a zonal pattern, where CD117 staining was similarly decreased, reflecting clonal heterogeneity. In contrast to GIST, SERCA3 immunostaining of spindle cell tumours and other gastrointestinal tumours resembling GIST was negative or weak. In conclusion, SERCA3 immunohistochemistry may be useful for the diagnosis of GIST with high confidence, when used as a third marker in parallel with KIT and DOG1. Moreover, SERCA3 immunopositivity may be particularly helpful in cases with negative or weak KIT or DOG1 staining, a situation that may be encountered de novo, or during the spontaneous or therapy-induced clonal evolution of GIST.

Gastrointestinal Stromal Tumors: Diagnosis, Follow-up and Role of Radiomics in a Single Center Experience

Gastrointestinal stromal tumors (GISTs) arise from the interstitial cells of Cajal in the gastrointestinal tract and are the most common intestinal tumors. Usually GISTs are asymptomatic, especially small tumors that may not cause any symptoms and may be found accidentally on abdominal CT scans. Discovering of inhibitor of receptor tyrosine kinases has changed the outcome of patients with high-risk GISTs. This paper will focus on the role of imaging in diagnosis, characterization and follow-up. We shall also report our local experience in radiomics evaluation of GISTs.

[Gastrointestinal stromal tumors (GIST)]

Gastrointestinal stromal tumors (GIST) are rare tumors with a varying malignancy potential, most frequently located in the stomach and the small intestine. The median age at diagnosis is around 65 years. Standard treatment of localized disease is complete surgical resection. A GIST is generally resistant to conventional chemotherapy. Most GISTs harbor tyrosine kinase activating mutations in either the KIT or PDGFRA proto-oncogene. The standard treatment of locally advanced and metastatic GIST with such mutations is the tyrosine kinase inhibitor imatinib. In cases of progressive disease after successive treatment with imatinib, sunitinib, and regorafenib, a fourth-line therapy with ripretinib was recently approved. Approved in 2020, avapritinib is the first effective targeted therapy for advanced stage GIST harboring an imatinib-resistant PDGFRA D842V mutation.

[18F]FAPI-42 PET/CT versus [18F]FDG PET/CT for imaging of recurrent or metastatic gastrointestinal stromal tumors

PURPOSE

PET has been important for monitoring recurrence and metastasis of Gastrointestinal Stromal Tumors (GISTs) and the selection of therapeutic strategies. A significant portion of GISTs lesions show negative FDG uptake and therefore calls for more tumor-specific imaging biomarkers. This study compared the imaging performance of [¹⁸F]FAPI-42 PET/CT and [¹⁸F]FDG PET/CT in recurrent or metastatic gastrointestinal stromal tumors (R/M GISTs).

METHODS

This study retrospectively included 35 patients with R/M GISTs who underwent both FAPI PET/CT and FDG PET/CT. The definite diagnosis was confirmed by pathology or follow-up drug treatment effects. The differences in detection rates and tumor-to-background SUV_max ratio (SUV_TBR) of different locations between dual-tracer PET/CT were compared. Factors including tumor size, degree of enhancement, type of gene mutation, and targeted treatment potentially influencing the uptake of both tracers were assessed. The excised lesions (n = 3) underwent immunohistochemical staining to verify FAP expression in the tissue.

RESULTS

A total of 106 lesions in 35 patients were identified, out of which 38/106 (35.8%) lesions (FAPI + /FDG -) were additionally detected by FAPI PET/CT as compared to that by FDG, including 26 liver metastases, ten peritoneal metastases, one gastrointestinal recurrence, and one bone metastasis. The positive detection rate of FAPI PET/CT for recurrent or metastatic GISTs was higher than that of FDG (80.2% vs. 53.8%,  P< 0.001), especially in liver metastases (87.5% vs. 33.3%, P< 0.001). Moreover, the SUV_TBR of liver metastases of GISTs in FAPI PET/CT was higher than that in FDG [2.4 (0.3 to 11.2) vs. 0.9 (0.3 to 6.5), P< 0.001]. The longest diameter of tumors in the FDG-positive group was higher than that of the FDG-negative group (P= 0.005); still, it did not differ between the FAPI-positive group and the FAPI-negative group. No difference in the degree of enhancement was observed between both tracers' positive and negative groups. Besides, the SUV_TBR of FDG but not FAPI differed significantly among various gene mutations (P< 0.001) as well as the targeted therapy and no targeted therapy groups (P= 0.001). FAP was expressed in R/M GISTs, and the uptake of FAPI corresponded to the level of FAP expression.

CONCLUSION

In conclusion, FAPI for imaging of R/M GISTs could be superior to FDG, specifically for liver metastases. The uptake of FAPI could reflect the level of FAP expression, and it was independent of tumor size, degree of enhancement, type of gene mutation, and targeted therapy as compared to FDG.

Gastrointestinal stromal tumors: a comprehensive radiological review

Gastrointestinal stromal tumors (GISTs) originating from the interstitial cells of Cajal in the muscularis propria are the most common mesenchymal tumor of the gastrointestinal tract. Multiple modalities, including computed tomography (CT), magnetic resonance imaging (MRI), fluorodeoxyglucose positron emission tomography, ultrasonography, digital subtraction angiography, and endoscopy, have been performed to evaluate GISTs. CT is most frequently used for diagnosis, staging, surveillance, and response monitoring during molecularly targeted therapy in clinical practice. The diagnosis of GISTs is sometimes challenging because of the diverse imaging findings, such as anatomical location (esophagus, stomach, duodenum, small bowel, colorectum, appendix, and peritoneum), growth pattern, and enhancement pattern as well as the presence of necrosis, calcification, ulceration, early venous return, and metastasis. Imaging findings of GISTs treated with antineoplastic agents are quite different from those of other neoplasms (e.g. adenocarcinomas) because only subtle changes in size are seen even in responsive lesions. Furthermore, the recurrence pattern of GISTs is different from that of other neoplasms. This review discusses the advantages and disadvantages of each imaging modality, describes imaging findings obtained before and after treatment, presents a few cases of complicated GISTs, and discusses recent investigations performed using CT and MRI to predict histological risk grade, gene mutations, and patient outcomes.

Hepatic GIST metastases: an illustrative case series

Gastrointestinal stromal tumours (GISTs) are uncommon mesenchymal tumours affecting the gastrointestinal tract. The liver is one of the most common sites for metastatic disease from GISTs and may exhibit a variety of CT and MR imaging appearances. These imaging features can vary prior to and following treatment with tyrosine kinase inhibitors. We report on the spectrum of imaging appearances of hepatic GIST metastases on multiphase contrast CT imaging and hepatocyte-specific contrast enhanced MR. To our knowledge, there are no published series specifically focusing on the appearances of liver metastases from GISTs.

An awareness of the protean appearances and pitfalls on CT and MRI of hepatic GIST metastases, prior to and at different times along the treatment pathway, will assist in early diagnosis of liver metastases, accurate assessment of tumour response and detection of recurrent metastatic disease.

Gastrointestinal Stromal Tumor (GIST) from esophagus to anorectum - diagnosis, response evaluation and surveillance on computed tomography (CT) scan

Gastrointestinal stromal tumor (GIST) are the most common non epithelial tumor of the gastrointestinal (GI) tract. They arise from interstitial cells of Cajal present in the myenteric plexus. They can also arise outside the GI tract from mesentery, retro peritoneum and omentum. With the advent of new targeted molecular therapy c- tyrosine kinase inhibitor (Imatinib), it has become important to differentiate between response and pseudo-progression of the disease as response evaluation criteria for GIST are different from Response Evaluation Criteria in Solid Tumors (RECIST). Purpose of this pictorial essay is to enumerate the characteristic CT features of GIST, and discuss atypical features and response evaluation criteria.

Multimodality Approach in Detection and Characterization of Hepatic Metastases

Early detection of liver metastases is important in patients with known primary malignancies. This plays an important role in treatment planning and impacts on further management of certain primary malignancies.

Magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography-computed tomography scans are reported to have high accuracy in the diagnosis of intrahepatic lesions. MRI in particular has the advantages of its high tissue sensitivity and its multiparametric approach.

Hepatic metastatic lesions have considerable overlap in their radiological appearance, and in this article the imaging appearance of various hepatic metastasis and approach is described.

Cancer genome landscape: a radiologist's guide to cancer genome medicine with imaging correlates

The introduction of high throughput sequence analysis in the past decade and the decrease in sequencing costs has made available an enormous amount of genomic data. These data have shaped the landscape of cancer genome, which encompasses mutations determining tumorigenesis, the signaling pathways involved in cancer growth, the tumor heterogeneity, and its role in development of metastases. Tumors develop acquiring a series of driver mutations over time. Of the many mutated genes present in cancer, only few specific mutations are responsible for invasiveness and metastatic potential, which, in many cases, have characteristic imaging appearance. Ten signaling pathways, each with targetable components, have been identified as responsible for cancer growth. Blockage of any of these pathways form the basis for molecular targeted therapies, which are associated with specific pattern of response and toxicities. Tumor heterogeneity, responsible for the different mutation pattern of metastases and primary tumor, has been classified in intratumoral, intermetastatic, intrametastatic, and interpatient heterogeneity, each with specific imaging correlates. The purpose of this article is to introduce the key components of the landscapes of cancer genome and their imaging counterparts, describing the types of mutations associated with tumorigenesis, the pathways of cancer growth, the genetic heterogeneity involved in metastatic disease, as well as the current challenges and opportunities for cancer genomics research.

[Ablative therapy of small renal masses]

Renal cell cancer is nowadays predominantly diagnosed in early stages due to the widespread use of sectional imaging for unrelated symptoms. Small renal masses (<4 cm) feature a largely indolent biology with a very low risk for metastasis or even a benign biology in up to 30% of the cases. Consequently, there is a need for less invasive therapeutic alternatives to nephron-sparing surgery. Meanwhile, there is a broad portfolio of local ablation techniques to treat small renal tumors. These include the extensively studied radiofrequency ablation and cryoablation techniques as well as newer modalities like microwave ablation and irreversible electroporation as more experimental techniques. Tumor ablation can be performed percutaneously under image guidance or laparoscopically. In particular, the percutaneous approach is a less invasive alternative to nephron-sparing surgery with lower risk for complications. Comparative studies and meta-analyses report a higher risk for local recurrence after renal tumor ablation compared to surgery. However, long-term oncological results after treatment of small renal masses are promising and do not seem to differ from partial nephrectomy. The possibility for salvage therapy in case of recurrence also accounts for this finding. Especially old patients with an increased risk of surgical and anesthesiological complications as well as patients with recurrent and multiple hereditary renal cell carcinomas may benefit from tumor ablation. Tumor biopsy prior to intervention is associated with very low morbidity rates and is oncologically safe. It can help to assess the biology of the renal mass and prevent therapy of benign lesions.

Malignant Extra-Gastrointestinal Stromal Tumor of the Mesentery

Gastrointestinal stromal tumors (GISTs), the commonest mesenchymal tumors of gastrointestinal tract are often described to take origin from the interstitial cells of Cajal (ICC) or its precursor cells. Rarely these tumors do arise in structures other than the alimentary tract like omentum, mesentery, retroperitoneum, etc., of varying malignant potential and are known as extra-gastrointestinal stromal tumors (eGISTs).

This is a case report of a 70-year-old female with multicentric malignant eGISTs arising in the mesentery of ileum. On laparotomy, a large mass of 20 × 15 cm was found in the small bowel mesentery without involvement of the adjacent ileum, with multiple other small nodules resembling lymph nodes, present adjacent to it. Histopathological study of the excised lump, confirmed the mass to be malignant eGIST without involvement of the adjacent ileum, with cluster differentiation (CD)117 positive and of high-risk stratification. The mesenteric nodule was confirmed on histopathology to be malignant eGIST, similar to that of that of the primary, without any lymphoid tissue. Adjuvant imatinib mesylate treatment was started immediately postoperation with the patient doing well at 1 year of follow-up. We report this case, due to the rare occurrence of multifocal malignant eGISTS of small bowel mesentery, which is yet to be reported. The existing literature is unclear regarding the clinicopathology and management of multifocal malignant stromal tumors of the mesentery.

Imaging surveillance of gastrointestinal stromal tumour: current recommendation by National Comprehensive Cancer Network and European Society of Medical Oncology-European Reference Network for rare adult solid cancers

Imaging plays an active role in the surveillance of gastrointestinal stromal tumours (GISTs). Risk stratification schemes, based on size, mitotic count, and anatomical site of origin of the GIST, help in planning preoperative and postoperative imaging strategies especially in determining the frequency and duration of surveillance; however, there is no clear consensus on the optimal imaging strategies in patients with GISTs who are completely cured by surgery and patients who are at risk of recurrence. In addition, current surveillance protocols depend on the resectability of the primary tumour and presence of metastatic disease. The objective of this article is to provide a comprehensive review of the role of the different imaging methods for surveillance of GISTs, focusing on the guidelines recommended by National Comprehensive Cancer Network and European Society of Medical Oncology - European Network for Rare adult solid Cancers, and to propose practical guidelines for surveillance of GISTs for various risk categories.

Tumor Response Assessment for Precision Cancer Therapy: Response Evaluation Criteria in Solid Tumors and Beyond

Objective assessment of tumor responses and treatment results has been the basis for the advancement of cancer therapies, and imaging plays a key role to provide a "common language" to describe the results of cancer treatment. Although Response Evaluation Criteria in Solid Tumors (RECIST) has been the most widely accepted method for assessing tumor response in the past decades, the limitations of RECIST have increasingly becoming recognized, especially with the recent advances of precision-medicine approaches to cancer. This article reviews the current concept of tumor response evaluations based on RECIST, describes the limitations of RECIST, and proposes strategies to overcome the limitations. The article emphasizes specific limitations in the setting of precision cancer therapy and cancer immunotherapy and discusses the important insights provided by the cutting-edge investigations in the emerging fields.

Imaging pediatric gastrointestinal stromal tumor (GIST)

BACKGROUND

Gastrointestinal stromal tumors (GIST) are extremely rare in children. Imaging plays a key role in staging and monitoring therapy (surgical and with tyrosine kinase inhibitors). The vast majority of articles addressing imaging of GIST base on adults and are based on CT. The subtype "pediatric GIST" - if at all - is only mentioned in a dependent clause. Although the imaging features in children and adults are similar, histology, clinical course and thus imaging approach are different.

METHODS

A PubMed search using the search terms "Gastrointestinal stromal tumor, GIST, WT GIST, children, pediatric, carney's triad, imaging, staging, follow-up, MRI, CEUS, ultrasonography, Positron emission tomography" was conducted. Studies that reported on laparoscopy, endoscopy and surgical techniques only were excluded.

RESULTS

Based on our selective literature review, we present alternative radiological imaging strategies using MRI, contrast enhanced ultrasound (CEUS) and PET-CT to stage and follow-up pediatric GIST patients. As pediatric GIST often is a chronic disease, minimizing exposure to ionizing radiation is mandatory.

CONCLUSION

MRI, contrast enhanced ultrasound and PET-CT instead of CT are the imaging modalities to evaluate pediatric GIST.

TYPE OF STUDY

Systematic review LEVEL OF EVIDENCE: III.

Evaluation of Alterations in Tumor Tissue of Gastrointestinal Stromal Tumor (GIST) in Computed Tomography Following Treatment with Imatinib

Background

The aim of this study was to evaluate the alterations in the neoplastic tissue of GIST following Imatinib treatment.

Material/Methods

CT studies of 14 patients with inoperable primary tumors and 56 patients with metastatic and recurrent disease after chemotherapy were analyzed retrospectively. The following alterations in features of primary and secondary tumors were analyzed: dimension, degree and type of contrast enhancement, outlines of lesions, presence of intratumoral bleeding, presence of calcifications.

Results

In the analyzed group of primary, metastatic and recurrent tumors after treatment with Imatinib in most cases a decrease in size and contrast enhancement were observed; the outlines of lesions became well circumscribed. Following the treatment, the number of tumors enhancing inhomogeneously decreased. In primary tumors the percentage of calcifications increased, whereas in metastatic tumors calcifications were observed only after treatment. There was no bleeding found within primary tumors after treatment. In metastatic disease, increased percentage of tumors with transient intratumoral bleeding was observed. There were also some unconventional CT images following treatment, such as: cystic transformation of lesions, enlargement of lesions, appearing of new lesions suggesting progression of the disease, stationary dimensions of lesions during local progression of the disease, simultaneous decrease and increase in size of metastatic lesions or appearance of new ones.

Conclusions

Right from the start of Imatinib therapy in inoperable and disseminated GIST patients, specific CT images, not seen during conventional cytotoxic chemotherapy, were observed.

Non-Gaussian diffusion imaging with a fractional order calculus model to predict response of gastrointestinal stromal tumor to second-line sunitinib therapy

PURPOSE

To demonstrate the clinical value of a non-Gaussian diffusion model using fractional order calculus (FROC) for early prediction of the response of gastrointestinal stromal tumor to second-line sunitinib targeted therapy.

METHODS

Fifteen patients underwent sunitinib treatment after imatinib resistance. Diffusion-weighted imaging with multiple b-values was performed before treatment (baseline) and 2 weeks (for early prediction of response) after initiating sunitinib treatment. Conventional MRI images at 12 weeks were used to determine the good and poor responders according to the modified Choi criteria for MRI. Diffusion coefficient D, fractional order parameter β (which correlates to intravoxel tissue heterogeneity), and a microstructural quantity µ were calculated using the FROC model. The FROC parameters and the longest diameter of the lesion, as well as their changes after 2 weeks of treatment, were compared between the good and poor responders. Additionally, the pretreatment FROC parameters were individually combined with the change in D (ΔD) using a logistic regression model to evaluate response to sunitinib treatment with a receiver operating characteristic analysis.

RESULTS

Forty-two good-responding and 32 poor-responding lesions were identified. Significant differences were detected in pretreatment β (0.67 versus 0.74, P = 0.011) and ΔD (45.7% versus 12.4%, P = 0.001) between the two groups. The receiver operating characteristic analysis showed that ΔD had a significantly higher predictive power than the tumor size change (area under the curve: 0.725 versus 0.580; 0.95 confidence interval). When ΔD was combined with pretreatment β, the area under the curve improved to 0.843 with a predictive accuracy of 75.7% (56 of 74).

CONCLUSIONS

The non-Gaussian FROC diffusion model showed clinical value in early prediction of gastrointestinal stromal tumor response to second-line sunitinib targeted therapy. The pretreatment FROC parameter β can increase the predictive accuracy when combined with the change in diffusion coefficient during treatment. Magn Reson Med 79:1399-1406, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Imaging therapy response of gastrointestinal stromal tumors (GIST) with FDG PET, CT and MRI: a systematic review

Purpose

Improvement of the therapeutic approaches in gastrointestinal stromal tumors (GIST) by the introduction of targeted therapies requires appropriate diagnostic tools, which allow sufficient assessment of therapeutic response, including differentiation of true progression from pseudoprogression due to myxoid degeneration or intratumoral hemorrhage. In this literature review the impact and limitations of different imaging modalities used in GIST therapy monitoring are discussed.

Methods

PubMed and Cochrane library search were performed using appropriate keywords. Overall, 39 original papers fulfilled the defined criteria and were included in this systematic review.

Results

Morphological imaging modalities like computed tomography (CT) are primarily used for both diagnosis and therapy monitoring. However, therapy with tyrosine kinase inhibitors and other targeted therapies in GIST may lead only to a minor tumor volume reduction even in cases of response. Therefore, the use of Response Evaluation Criteria in Solid Tumors (RECIST) has limitations. To overcome those limitations, modified response criteria have been introduced for the CT-based therapy assessment, like the Choi criteria as well as criteria based on dual energy CT studies. Functional imaging techniques, mostly based on FDG PET-CT are in use, in particular for the assessment of early treatment response.

Conclusions

The impact and the limitations of PET-based therapy monitoring, as well as its comparison with CT, MRI and survival data are discussed in this review. CT is still the standard method for the evaluation of therapy response despite its several limitations. FDG PET-CT is helpful for the assessment of early therapy response; however, more prospective data are needed to define its role as well as the appropriate time intervals for therapy monitoring. A multiparametric evaluation based on changes in both morphological and functional data has to be assessed in further prospective studies.

UK clinical practice guidelines for the management of gastrointestinal stromal tumours (GIST)

BACKGROUND

Soft tissue sarcomas (STS) are rare tumours arising in mesenchymal tissues. Gastrointestinal stromal tumour (GIST) is the commonest STS and arises within the wall of the gastrointestinal (GI) tract. While most GISTs occur in the stomach they do occur in all parts of the GI tract. As with other STS, it is important that GISTs are managed by expert teams, to ensure consistent and optimal treatment, as well as recruitment to clinical trials, and the ongoing accumulation of further knowledge of the disease. The development of appropriate guidance, by an experienced panel referring to the evidence available, is therefore a useful foundation on which to build progress in the field.

METHODOLOGY

British Sarcoma Group guidelines for the management of GIST were initially developed by a panel of physicians experienced in the management of GIST. This current version has been updated and amended with reference to other European and US guidance. We have received input from representatives of all diagnostic and treatment disciplines as well as patient representatives. Levels of evidence and strength of recommendation gradings are those used by ESMO adapted from those published by the Infectious Disease Society of America.

CONCLUSIONS

The guidelines cover aetiology, genetics and underlying molecular mechanisms, diagnosis and initial investigations, staging and risk stratification, surgery, neoadjuvant and adjuvant therapy, the management of advanced disease and follow-up. The importance of mutational analysis in guiding treatment is highlighted, since this can indicate the most effective treatment and avoid administration of ineffective drugs, emphasising the need for management in specialist centres.

Update on Gastrointestinal Stromal Tumors for Radiologists

The management of gastrointestinal stromal tumors (GISTs) has evolved significantly in the last two decades due to better understanding of their biologic behavior as well as development of molecular targeted therapies. GISTs with exon 11 mutation respond to imatinib whereas GISTs with exon 9 or succinate dehydrogenase subunit mutations do not. Risk stratification models have enabled stratifying GISTs according to risk of recurrence and choosing patients who may benefit from adjuvant therapy. Assessing response to targeted therapies in GIST using conventional response criteria has several potential pitfalls leading to search for alternate response criteria based on changes in tumor attenuation, volume, metabolic and functional parameters. Surveillance of patients with GIST in the adjuvant setting is important for timely detection of recurrences.

Soft-Tissue Sarcomas: An Update for Radiologists Based on the Revised 2013 World Health Organization Classification

OBJECTIVE

Soft-tissue sarcomas are a diverse group of malignancies, and our rapidly improving understanding of their molecular pathogenesis and treatment is leading to better clinical outcomes. The revised 2013 World Health Organization (WHO) classification of soft-tissue sarcomas introduced several important changes. We provide a comprehensive overview of the relevant changes for radiologists.

CONCLUSION

Rapid advances in the understanding of the pathogenesis and molecular biology of soft-tissue sarcomas led to major revisions in the 2013 WHO classification. To provide optimal multidisciplinary patient care, radiologists must remain up-to-date with the latest developments in the field of soft-tissue sarcomas to best correlate the histologic and imaging features of the various types of tumors and understand the unique patterns of treatment response and disease recurrence.

The standard diagnosis, treatment, and follow-up of gastrointestinal stromal tumors based on guidelines

Although gastrointestinal stromal tumors (GISTs) are a rare type of cancer, they are the commonest sarcoma in the gastrointestinal tract. Molecularly targeted therapy, such as imatinib therapy, has revolutionized the treatment of advanced GIST and facilitates scientific research on GIST. Nevertheless, surgery remains a mainstay of treatment to obtain a permanent cure for GIST even in the era of targeted therapy. Many GIST guidelines have been published to guide the diagnosis and treatment of the disease. We review current versions of GIST guidelines published by the National Comprehensive Cancer Network, by the European Society for Medical Oncology, and in Japan. All clinical practice guidelines for GIST include recommendations based on evidence as well as on expert consensus. Most of the content is very similar, as represented by the following examples: GIST is a heterogeneous disease that may have mutations in KIT, PDGFRA, HRAS, NRAS, BRAF, NF1, or the succinate dehydrogenase complex, and these subsets of tumors have several distinctive features. Although there are some minor differences among the guidelines--for example, in the dose of imatinib recommended for exon 9-mutated GIST or the efficacy of antigen retrieval via immunohistochemistry--their common objectives regarding diagnosis and treatment are not only to improve the diagnosis of GIST and the prognosis of patients but also to control medical costs. This review describes the current standard diagnosis, treatment, and follow-up of GISTs based on the recommendations of several guidelines and expert consensus.

Prognostic factors after imatinib secondary resistance: survival analysis in patients with unresectable and metastatic gastrointestinal stromal tumors

BACKGROUND

Patients undergoing imatinib therapy for gastrointestinal stromal tumors (GISTs) show drug resistance during treatment in the late stages. The aims of this study were to determine survival after the appearance of imatinib secondary resistance (ISR) and to identify the prognostic factors.

METHODS

Eligible were patients with unresectable and metastatic GISTs who were diagnosed with ISR and/or underwent treatment for ISR in our institution between 2001 and 2012. A total of 48 patients were enrolled and overall survival was retrospectively analyzed. The Cox proportional hazards model was used to identify the independent prognostic factors. Median follow-up time was 58 months.

RESULTS

As of the cutoff date, 41 of the 48 patients with ISR had died, of which 39 died of GISTs. The overall 1-, 3-, and 5-year survival rates of the 48 patients were 64.6, 32.8, and 20.4 %, respectively, and median survival time was 22 months. The favorable independent prognostic factors identified were long progression-free survival in first-line imatinib therapy (P = 0.04), small diameter of progressive disease (PD) (P = 0.02), and surgical resection of PD (P = 0.01).

CONCLUSION

Surgical resection of PD in selected cases could improve prognosis in ISR patients undergoing GIST treatment.

Tyrosine kinase inhibitors in the treatment of unresectable or metastatic gastrointestinal stromal tumors

INTRODUCTION

Gastrointestinal stromal tumor (GIST) is the most common sarcoma of the gastrointestinal tract. Proliferation of GIST is driven by activating mutations in the KIT or PDGFRA genes that found in most sporadic GISTs. Surgery is the main remedial measure for primary GIST, and imatinib is the principal therapeutic of choice for unresectable or metastatic GIST. Imatinib revolutionized treatment for unresectable or metastatic GISTs; however, resistance to imatinib has inevitably developed for most GIST patients.

AREAS COVERED

PubMed was searched to find biological studies of GIST and clinical trials of molecularly targeted agents on unresectable or metastatic GISTs, and the key papers found have been reviewed. In this paper, the standard therapy which includes imatinib, sunitinib and regorafenib for unresectable or metastatic GIST has been reviewed and molecular mechanisms of resistance for tyrosine kinase inhibitors (TKIs) have been postulated and discussed. Treatment measures for resistant GIST and therapeutic choices after the standard therapy have also been described.

EXPERT OPINION

The standard therapy for unresectable or metastatic GISTs is first-line imatinib, second-line sunitinib and third-line regorafenib. After standard therapy, best supportive care or clinical trials is recommended in the guidelines. However, patients may benefit from continuation of TKIs beyond disease progression and from rechallenge of TKIs used previously.

Considering the role of radiation therapy for gastrointestinal stromal tumor

Gastrointestinal stromal tumors (GISTs) are rare mesenchymal tumors arising in the gastrointestinal tract. Over the last decade, the management and prognosis of GISTs has changed dramatically with molecular characterization of the c-kit mutation and the adoption of targeted systemic therapy. Currently, the standard of care for resectable tumors is surgery, followed by adjuvant imatinib for tumors at high risk for recurrence. Inoperable or metastatic tumors are treated primarily with imatinib. Despite excellent initial response rates, resistance to targeted therapy has emerged as a common clinical problem, with relatively few therapeutic solutions. While the treatment of GISTs does not commonly include radiotherapy, radiation therapy could be a valuable contributing modality. Several case reports indicate that radiation can control locally progressive, drug-resistant disease. Further study is necessary to define whether radiation could potentially prevent or delay the onset of drug resistance, or improve outcomes when given in combination with imatinib.

Spectrum of multilocular cystic hepatic lesions: CT and MR imaging findings with pathologic correlation

A multilocular cystic hepatic lesion detected at computed tomography (CT) and magnetic resonance (MR) imaging is a common but nonspecific radiologic finding that can cause potential challenges for differential diagnosis. This imaging pattern may be observed in a wide spectrum of common and uncommon neoplastic or nonneoplastic entities. Neoplastic lesions include cystadenoma, cystadenocarcinoma, hepatocellular carcinoma (HCC), metastases, mesenchymal hamartoma, and inflammatory myofibroblastic tumor. Nonneoplastic lesions include hepatic abscess, echinococcal cyst, intrahepatic hematoma, and biloma. The multiple coalescent cysts seen in polycystic liver disease may exhibit an imaging pattern similar to that of a multilocular cystic lesion. Mural nodularity, irregular thickness of the septa, ragged inner surface, and typical enhancement pattern in the solid portion of the lesion are often indicative of malignancy, although multilocular primary or secondary malignant tumors are uncommon. Recognition of the more common necrosis or cystic change of HCC and metastases induced by locoregional or systemic treatment also is important. The nonenhanced cystic component may be composed of different types of fluids (eg, serous, mucinous, proteinaceous, hemorrhagic, bilious, or mixed) or spontaneous or treatment-related necrosis, whereas the septa may be formed by a wide range of tissues depending on the lesion type. An understanding of the CT and MR imaging findings of these lesions and their respective pathologic correlation aids in accurate diagnosis.

A radiologist's guide to treatment response criteria in oncologic imaging: anatomic imaging biomarkers

OBJECTIVE

The purpose of this article is to describe the imaging biomarkers of treatment response and provide an overview of anatomic imaging biomarkers.

CONCLUSION

Imaging biomarkers of treatment response have evolved into the primary endpoint of response in most phase 2 studies. Anatomic imaging biomarkers are applied to depict change in tumor size in response to treatment and are currently the most commonly applied method of treatment response evaluation.

The effects of surgical cytoreduction prior to imatinib therapy on the prognosis of patients with advanced GIST

BACKGROUND

Baseline tumor size is one of important prognostic factors for imatinib therapy in patients with advanced gastrointestinal stromal tumor (GIST). The purpose of this study was to determine whether surgical cytoreduction before imatinib therapy can improve the prognosis.

METHODS

A total of 249 patients with advanced GIST were reviewed retrospectively. Patients were categorized into two groups according to the degree of initial cytoreduction: 35 patients with ≥75 % of initial tumor bulk removed (cytoreduction group) and the other 214 patients (no cytoreduction group). The median follow-up was 44.0 months.

RESULTS

Patients in the cytoreduction group were younger, in better performance, showed more initially metastatic disease, peritoneal metastases, but fewer liver metastases. The baseline tumor size when starting imatinib became significantly reduced in the cytoreduction group, which made significant difference between the two groups. By multivariate analyses, mutational status, tumor size, and granulocyte count at presentation were associated with progression-free survival. Age and tumor size were associated with overall survival. However, initial cytoreduction was not significantly related to the prognosis.

CONCLUSIONS

Cytoreduction before imatinib therapy appears not to improve the prognosis. Imatinib therapy should still represent the initial treatment for advanced GIST.

The benefit of using CT-perfusion imaging for reliable response monitoring in patients with gastrointestinal stromal tumor (GIST) undergoing treatment with novel targeted agents

Solely size-based response criteria may be unreliable in patients with gastrointestinal stromal tumors (GIST) treated with tyrosine kinase inhibitors, because they typically underestimate responses to treatment. As GISTs are generally hypervascularized and novel targeted drugs knowingly affect angiogenic signaling pathways, perfusion measurements are expected to deliver important information about their efficacy. This pictorial essay illustrates the benefit of using complementary CT-perfusion-based measurements for more accurate evaluation of response to therapy in GIST.

Comparison of WHO and RECIST criteria for evaluation of clinical response to chemotherapy in patients with advanced breast cancer

When patients with advanced breast cancer (ABC) are treated with neoadjuvant chemotherapy (NACT), efficacy is monitored by the extent of tumor shrinkage. Since their publication in 1981, World Health Organization (WHO) guidelines have been widely practiced in clinical trials and oncologic practice, for standardized tumor response evaluation. With advances in cancer treatment and tumor imaging, a simpler criterion based on one-dimensional rather than bi-dimensional (WHO) tumor measurement, named Response Evaluation Criteria in Solid Tumors (RECIST) was introduced in 2000. Both approaches have four response categories: complete response, partial response, stable disease and progressive disease (PD). Bi-dimensional measurement data of 151 patients with ABC were analysed with WHO and RECIST criteria to compare their response categories and inter criteria reproducibility by Kappa statistics. There was 94% concordance and 9/151 patients were re-categorized with RECIST including 6/12 PD cases. RECIST therefore under-estimates and delays diagnosis of PD. This is undesirable because it may delay or negate switch over to alternate therapy. Analysis was repeated with a new criteria named RECIST-Breast (RECIST-B), with a lower threshold for PD (≥10% rather than ≥20% increase of RECIST). This showed higher concordance of 97% with WHO criteria and re-categorization of only 4/151 patients (1/12 PD cases). RECIST-B criteria therefore have advantages of both ease of measurement and calculations combined with excellent concordance with WHO criteria, providing a practical clinical tool for response evaluation and offering good comparison with past and current clinical trials of NACT using WHO guidelines.

Antiproliferative effects of continued mitogen-activated protein kinase pathway inhibition following acquired resistance to BRAF and/or MEK inhibition in melanoma

Inhibitors of the mitogen-activated protein kinases (MAPK), BRAF, and MAP-ERK kinase (MEK) induce tumor regression in the majority of patients with BRAF-mutant metastatic melanoma. The clinical benefit of MAPK inhibitors is restricted by the development of acquired resistance with half of those who benefit having progressed by 6 to 7 months and long-term responders uncommon. There remains no agreed treatment strategy on disease progression in these patients. Without published evidence, fears of accelerated disease progression on inhibitor withdrawal have led to the continuation of drugs beyond formal disease progression. We now show that treatment with MAPK inhibitors beyond disease progression can provide significant clinical benefit, and the withdrawal of these inhibitors led to a marked increase in the rate of disease progression in two patients. We also show that MAPK inhibitors retain partial activity in acquired resistant melanoma by examining drug-resistant clones generated to dabrafenib, trametinib, or the combination of these drugs. All resistant sublines displayed a markedly slower rate of proliferation when exposed to MAPK inhibitors, and this coincided with a reduction in MAPK signaling, decrease in bromodeoxyuridine incorporation, and S-phase inhibition. This cytostatic effect was also associated with diminished levels of cyclin D1 and p-pRb. Two short-term melanoma cultures generated from resistant tumor biopsies also responded to MAPK inhibition, with comparable inhibitory changes in proliferation and MAPK signaling. These data provide a rationale for the continuation of BRAF and MEK inhibitors after disease progression and support the development of clinical trials to examine this strategy.

Molecular targeted therapies in non-GIST soft tissue sarcomas: what the radiologist needs to know

Non-gastrointestinal stromal soft tissue sarcomas are uncommon neoplasms that have a dismal prognosis due to a high incidence of metastases and a poor response to conventional chemotherapy. The identification of characteristic genetic alterations in several of these tumors has opened the window for molecular targeted therapies in patients who have failed conventional chemotherapy. Imaging plays a critical role in assessing the response to these novel therapeutic agents. Just like the response of gastrointestinal stromal tumors to imatinib, the response of non-gastrointestinal stromal soft tissue sarcomas to molecular targeted drugs is better evaluated on imaging by alternate tumor response criteria such as the Choi criteria. In addition, these drugs are associated with distinct class-specific drug toxicities that can come to attention for the first time on imaging. The purpose of this article is to provide a primer for the radiologist on the various molecular targeted therapies in advanced/metastatic non-gastrointestinal stromal soft tissue sarcomas with emphasis on the role of imaging in assessing treatment response and complications.

Gastrointestinal stromal tumor--background, pathology, treatment

Gastrointestinal stromal tumor (GIST) represents the most common mesechymal tumor of the gastrointestinal tract. Discovery of the relationship between unregulated KIT kinase and GIST transformation has led to diagnostic and therapeutic targeting. Imatinib is the recommended first-line treatment of metastatic GIST. In addition, the combination of surgery and imatinib for primary GIST is indicated in the adjuvant setting of high-risk patients and there may be benefit for this combination in the neoadjuvant setting. The success of molecular targeted therapy in GIST represents an important and exciting advance in solid tumor oncology.

Tumor response and clinical outcome in metastatic gastrointestinal stromal tumors under sunitinib therapy: comparison of RECIST, Choi and volumetric criteria

PURPOSE

Purpose of the study was to compare radiological treatment response according to RECIST, Choi and volumetry in GIST-patients under 2nd-line-sunitinib-therapy and to correlate the results of treatment response assessment with disease-specific survival (DSS).

PATIENTS AND METHODS

20 patients (mean: 60.7 years; 12 male/8 female) with histologically proven GIST underwent baseline-CT of the abdomen under imatinib and follow-up-CTs 3 months and 1 year after change to sunitinib. 68 target lesions (50 hepatic, 18 extrahepatic) were investigated. Therapy response (partial response (PR), stable disease (SD), progressive disease (PD)) was evaluated according to RECIST, Choi and volumetric criteria. Response according to the different assessment systems was compared and correlated to the DSS of the patients utilizing Kaplan-Meier statistics.

RESULTS

The mean DSS (in months) of the response groups 3 months after therapy change was: RECIST: PR (0/20); SD (17/20): 30.4 (months); PD (3/20) 11.6. Choi: PR (10/20) 28.6; SD (8/20) 28.1; PD (2/20) 13.5. Volumetry: PR (4/20) 29.6; SD (11/20) 29.7; PD (5/20) 17.2. Response groups after 1 year of sunitinib showed the following mean DSS: RECIST: PR (3/20) 33.6; SD (9/20) 29.7; PD (8/20) 20.3. Choi: PR (10/20) 21.5; SD (4/20) 42.9; PD (6/20) 23.9. Volumetry: PR (6/20) 27.3; SD (5/20) 38.5; PD (9/20) 19.3.

CONCLUSION

One year after modification of therapy, only partial response according to RECIST indicated favorable survival in patients with GIST. The value of alternate response assessment strategies like Choi criteria for prediction of survival in molecular therapy still has to be demonstrated.

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.

The lack of CD34 expression in gastrointestinal stromal tumors is related to cystic degeneration following imatinib use

OBJECTIVE

We evaluated the characteristics of the gastrointestinal stromal tumors that showed discrepancies between their assessment using the Response Evaluation Criteria in Solid Tumor (RECIST) and Choi's criteria. We also investigated the clinical applicability of Choi's criteria to Korean gastrointestinal stromal tumor patients undergoing imatinib therapy.

METHODS

Patients with advanced gastrointestinal stromal tumors treated with frontline imatinib were analyzed. Computed tomography images of these patients were reviewed and genotyping for the KIT and PDGFRA genes was performed. Immunohistochemical staining of c-KIT, CD34, platelet derived growth factor receptor-alpha, platelet derived growth factor receptor-beta, AKT, P-ERK and vascular endothelial growth factor was followed.

RESULTS

Ninety-five patients were enrolled. When using Choi's criteria to evaluate the 61 patients who achieved at least partial response by Choi's criteria, 27 patients showed discrepancies in their response to treatment between these two sets of criteria. A lack of CD34 expression in tumors was found to be related to cystic degeneration after imatinib treatment (P=0.001). Patients who showed partial response by Choi's criteria but stable disease by RECIST criteria had a similar progression-free survival to cases who showed a partial response under both systems (P=0.951).

CONCLUSIONS

Gastrointestinal stromal tumors showing cystic degeneration after imatinib treatment lack CD34 expression. Choi's criteria have a clinical value in terms of the progression-free survival in Korean patients treated with imatinib.

Current management and prognostic features for gastrointestinal stromal tumor (GIST)

Stromal or mesenchymal neoplasms affecting the gastrointestinal (GI) tract have undergone a remarkable evolution in how they are perceived, classified, approached, diagnosed and managed over the last 30 years. Gastrointestinal stromal tumors (GIST) account for approximately 1% to 3% of all malignant GI tumors. The clinical features can vary depending on the anatomic location, size and aggressiveness of the tumor. Metastatic GIST represents a successful example of molecular targeted therapy. In this comprehensive review, we discuss the epidemiology, clinical features and diagnostic modalities for GIST. We also describe treatment options for early stage, locally advanced and metastatic GIST. Indications for neoadjuvant and adjuvant therapy along with duration of therapy are also explained. A brief discussion of latest biomarkers and updates from recent meetings is also provided.

Personalized tumor response assessment in the era of molecular medicine: cancer-specific and therapy-specific response criteria to complement pitfalls of RECIST

OBJECTIVE

The purpose of this article is to review cancer- and therapy-specific tumor response assessment criteria used in clinical trials and in practice, with illustrative case examples, and to discuss future directions toward "personalized" tumor response assessment.

CONCLUSION

Although Response Evaluation Criteria in Solid Tumors will remain as the primary generalized criteria for response assessment, newer cancer- and therapy-specific criteria will play an important role in providing state-of-the-art response assessment of tumor following molecular targeted therapy and will contribute to personalized cancer care in the era of molecular medicine.

Recent advances and novel agents for gastrointestinal stromal tumor (GIST)

The discovery of CD117 mutation in almost all gastrointestinal stromal tumors (GISTs) marked a milestone. Other spindle cell neoplasms arising from the GI tract including lipoma, schwannoma, hemangioma, leiomyoma, and leiomyosarcoma are typically CD117-negative. GIST research and clinical care now represent a paradigm of translating discoveries in the molecular pathogenesis of cancer into highly effective targeted therapies that selectively inhibit etiologic “driver” pathways, leading to dramatically improved clinical outcomes. A series of investigations and trials are underway to develop novel and effective ways to treat patients with GIST. In this review, we discuss the highlights of recent advances and novel agents for GIST therapy.

Consensus report on the radiological management of patients with gastrointestinal stromal tumours (GIST): recommendations of the German GIST Imaging Working Group

The aim was to reach consensus in imaging for staging and follow-up as well as for therapy response assessment in patients with gastrointestinal stromal tumours (GIST). The German GIST Imaging Working Group was formed by 9 radiologists engaged in assessing patients with GIST treated with targeted therapy. The following topics were discussed: indication and optimal acquisition techniques of computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET)/CT; tumour response assessment considering response criteria and measurement techniques on CT, MRI and PET/CT; result interpretation; staging interval and pitfalls. Contrast-enhanced CT is the standard method for GIST imaging. MRI is the method of choice in case of liver-specific questions or contraindications to CT. PET/CT should be used for early response assessment or inconclusive results on morphologic imaging. All imaging techniques should be standardized allowing a reliable response assessment. Response has to be assessed with respect to lesion size, lesion density and appearance of new lesions. A critical issue is pseudoprogression due to myxoid degeneration or intratumoural haemorrhage. The management of patients with GIST receiving a targeted therapy requires a standardized algorithm for imaging and an appropriate response assessment with respect to changes in lesion size and density.

Imatinib efficacy by tumor genotype in Korean patients with advanced gastrointestinal stromal tumors (GIST): The Korean GIST Study Group (KGSG) study

PURPOSE

To assess the efficacy of imatinib for different tumor genotypes in Korean patients with advanced gastrointestinal stromal tumors (GIST).

MATERIAL AND METHODS

Clinical data were collected from 370 consecutive patients with locally advanced unresectable, metastatic, or recurrent GIST treated with imatinib 400 mg/day between August 2001 and December 2007 at 20 Korean institutions. Tumor genotypes were determined for 290 patients by direct DNA sequencing of KIT exons 9, 11, 13, and 17, and PDGFRA exons 12, 14, and 18.

RESULTS

Of 290 patients assessed for genotype, 261 (90.0%) had mutations in KIT: 222 (76.6%) in exon 11, 35 (12.1%) in exon 9 and two each (0.7%) for exons 13 and 17. Four patients (1.4%) had mutations in the PDGFRA gene: one in exon 12, and three in exon 18. Twenty-five patients (8.6%) had no detectable mutations. The best responses of the 235 patients with measurable lesions were: 15 complete response (6.4%), 126 partial response (53.5%), 86 stable disease (36.6%), and eight progressive disease (3.4%). Patients with KIT exon 9 mutations, compared with patients with KIT exon 11 mutations, had a lower objective response rate (36.7% vs. 63.6%, p = 0.007) and a shorter progression-free survival (median 28.7 months vs. 49.4 months, p = 0.001). No statistical difference in overall survival was observed between these genotypes.

CONCLUSION

This study confirms that imatinib efficacy is dependent on genotype in Korean GIST patients, consistent with results demonstrated by Western patients with GIST.