Avapritinib in advanced PDGFRA D842V-mutant gastrointestinal stromal tumour (NAVIGATOR): a multicentre, open-label, phase 1 trial

Cancer-associated fibroblast secretion of PDGFC promotes gastrointestinal stromal tumor growth and metastasis

Targeted therapies for gastrointestinal stromal tumor (GIST) are modestly effective, but GIST cannot be cured with single agent tyrosine kinase inhibitors. In this study, we sought to identify new therapeutic targets in GIST by investigating the tumor microenvironment. Here, we identified a paracrine signaling network by which cancer-associated fibroblasts (CAFs) drive GIST growth and metastasis. Specifically, CAFs isolated from human tumors were found to produce high levels of platelet-derived growth factor C (PDGFC), which activated PDGFC-PDGFRA signal transduction in GIST cells that regulated the expression of SLUG, an epithelial-mesenchymal transition (EMT) transcription factor and downstream target of PDGFRA signaling. Together, this paracrine induce signal transduction cascade promoted tumor growth and metastasis in vivo. Moreover, in metastatic GIST patients, SLUG expression positively correlated with tumor size and mitotic index. Given that CAF paracrine signaling modulated GIST biology, we directly targeted CAFs with a dual PI3K/mTOR inhibitor, which synergized with imatinib to increase tumor cell killing and in vivo disease response. Taken together, we identified a previously unappreciated cellular target for GIST therapy in order to improve disease control and cure rates.

Liquid Biopsy in Gastrointestinal Stromal Tumors: Ready for Prime Time?

OPINION STATEMENT

Gastrointestinal stromal tumor (GIST) constitutes a paradigm for clinically effective targeted inhibition of oncogenic driver mutations. Therefore, GIST has emerged as a compelling clinical and biological model to study oncogene addiction and to validate preclinical concepts for drug response and drug resistance. Oncogenic activation of KIT or PDGFRA receptor tyrosine kinases is the essential drivers of GIST progression throughout all stages of the disease. Interestingly, KIT/PDGFRA genotype predicts the response to first-line imatinib and to all tyrosine kinase inhibitors (TKIs) approved or in investigation after imatinib failure. Considering that TKIs are effective only against a subset of KIT or PDGFRA resistance mutations, close monitoring of tumor dynamics with non-invasive methods such as liquid biopsy emerges as a necessary step forward in the field. Liquid biopsy, in contrast to solid tumor biopsy, aims to characterize tumors irrespective of heterogeneity. Although there are several components in the peripheral blood, most recent studies have been focused on circulating tumor (ct)DNA, due to the technological feasibility, the stability of DNA itself and DNA alterations, and the therapeutic development in precision oncology largely based on the identification of genetic driver mutations. In the present review, we systematically dissect the current wealth of data of ctDNA in GIST. To do so, a critical understanding of the promises and limitations of the current technologies will be followed by an exposition of the knowledge gathered with such studies in GIST. Collectively, our goal is to establish clear premises that can be used as the foundations to build future studies towards the clinical implementation of ctDNA evaluation in GIST patients.

Anti-Cancer Drugs Targeting Protein Kinases Approved by FDA in 2020

Cancers are a large group of diseases that mostly emerge because of the uncontrollable action of many different genes in human cells [...].

The Identity of PDGFRA D842V-Mutant Gastrointestinal Stromal Tumors (GIST)

Simple Summary

Among the platelet-derived growth factor receptor (PDGFRA) mutations in gastrointestinal stromal tumors (GIST), the most frequent is the substitution at position 842 in the A-loop of an aspartic acid (D) with a valine (V), widely recognized as D842V, a two-sided mutation providing primary resistance to all currently approved agents for GIST treatment. In recent years, new specific inhibitors have been studied in preclinical and clinical settings, and molecular findings have been accumulated, well describing this complex entity. This paper aims at offering a comprehensive picture of the clinical features and the molecular background of this rare subtype of GIST.

Abstract

The majority of gastrointestinal stromal tumors (GIST) carry a sensitive primary KIT mutation, but approximately 5% to 10% of cases harbor activating mutations of platelet-derived growth factor receptor (PDGFRA), mainly involving the A-loop encoded by exon 18 (~5%), or more rarely the JM domain, encoded by exon 12 (~1%), or the ATP binding domain encoded by exon 14 (<1%). The most frequent mutation is the substitution at position 842 in the A-loop of an aspartic acid (D) with a valine (V) in exon 18, widely recognized as D842V. This mutation, as well known, provides primary resistance to imatinib and sunitinib. Thus, until few years ago, no active drugs were available for this subtype of GIST. Conversely, recent years have witnessed the development of a new specific inhibitor—avapritinib—that has been studied in in vitro and clinical setting with promising results. In light of this primary resistance to conventional therapies, the biological background of D842V-mutant GIST has been deeply investigated to better understand what features characterize this peculiar subset of GIST, and some promising insights have emerged. Hereinafter, we present a comprehensive overview on the clinical features and the molecular background of this rare subtype of GIST.

Avapritinib in Patients With Advanced Gastrointestinal Stromal Tumors Following at Least Three Prior Lines of Therapy

BACKGROUND

Most gastrointestinal stromal tumors (GIST) driven by KIT or platelet-derived growth factor receptor A (PDGFRA) mutations develop resistance to available tyrosine kinase inhibitor (TKI) treatments. NAVIGATOR is a two-part, single-arm, dose escalation and expansion study designed to evaluate safety and antineoplastic activity of avapritinib, a selective, potent inhibitor of KIT and PDGFRA, in patients with unresectable or metastatic GIST.

MATERIALS AND METHODS

Eligible patients were 18 years or older with histologically or cytologically confirmed unresectable GIST and Eastern Cooperative Oncology Group performance status ≤2 and initiated avapritinib at 300 mg or 400 mg once daily. Primary endpoints were safety in patients who initiated avapritinib at 300 mg or 400 mg once daily and overall response rate (ORR) in patients in the safety population with three or more previous lines of TKI therapy.

RESULTS

As of November 16, 2018, in the safety population (n = 204), the most common adverse events (AEs) were nausea (131 [64%]), fatigue (113 [55%]), anemia (102 [50%]), cognitive effects (84 [41%]), and periorbital edema (83 [41%]); 17 (8%) patients discontinued due to treatment-related AEs, most frequently confusion, encephalopathy, and fatigue. ORR in response-evaluable patients with GIST harboring KIT or non-D842V PDGFRA mutations and with at least three prior therapies (n = 103) was 17% (95% confidence interval [CI], 10-25). Median duration of response was 10.2 months (95% CI, 7.2-10.2), and median progression-free survival was 3.7 months (95% CI, 2.8-4.6).

CONCLUSION

Avapritinib has manageable toxicity with meaningful clinical activity as fourth-line or later treatment in some patients with GIST with KIT or PDGFRA mutations.

IMPLICATIONS FOR PRACTICE

In the NAVIGATOR trial, avapritinib, an inhibitor of KIT and platelet-derived growth factor receptor A tyrosine kinases, provided durable responses in a proportion of patients with advanced gastrointestinal stromal tumors (GIST) who had received three or more prior therapies. Avapritinib had a tolerable safety profile, with cognitive adverse events manageable with dose interruptions and modification in most cases. These findings indicate that avapritinib can elicit durable treatment responses in some patients with heavily pretreated GIST, for whom limited treatment options exist.

[Treatment of soft tissue sarcomas including GIST - Update 2021]

Soft tissue sarcomas are rare tumors that represent a major challenge due to varying clinical presentations and often interdisciplinary treatment concepts. Gold standard for the treatment of localized resectable soft tissue sarcomas is complete surgical removal. So far, multimodality treatment does not represent a clininal standard. However, several newer analyses and studies suggest that a subgroup of patients seems to derive an overall survival benefit from perioperative chemotherapy. In metastatic soft tissue sarcoma systemic therapy is the treatment of choice. Most active drugs are the anthracyclines and ifosfamide. Combination chemotherapy has improved both response rate and progression-free survival at the costs of increased toxicity in comparison to single agent therapy but without impact on overall survival in first-line therapy. In pretreated patients, treatment options consist of trabectedin, pazopanib, gemcitabine plus docetaxel or DTIC, and eribulin. Recent data have shown that histiotype-specific treatment options including targeted therapy represent a major improvement for several sarcoma subtypes.In GIST, imatinib is the gold standard for patients with advanced or metastatic disease. In imatinib refractory or intolerant patients, sunitinib in an individualized treatment schedule is recommended. Regorafenib has been approved for third-line therapy. Recently, avapritinib has been approved for treatment of patients with the so far resistant D842V mutation in the PDGFRA exon 18. Ripretinib has shown very promising activity in forth and further lines of therapy and is already approved in the US. The use of adjuvant imatinib therapy in patients with completely resected localized GIST with a high risk of recurrence has significantly improved overall survival with a treatment duration of 3 years. These results have now been confirmed with a 10 years follow-up analysis.

Update on Molecular Genetics of Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. The majority are sporadic, solitary tumors that harbor mutually exclusive KIT or PDGFRA gain-of-function mutations. The type of mutation in addition to risk stratification corresponds to the biological behavior of GIST and response to treatment. Up to 85% of pediatric GISTs and 10–15% of adult GISTs are devoid of these (KIT/PDGFRA) mutations and are referred to as wild-type GISTs (wt-GIST). It has been shown that these wt-GISTs are a heterogeneous tumor group with regard to their clinical behavior and molecular profile. Recent advances in molecular pathology helped to further sub-classify the so-called “wt-GISTs”. Based on their significant clinical and molecular heterogeneity, wt-GISTs are divided into a syndromic and a non-syndromic (sporadic) subgroup. Recently, the use of succinate dehydrogenase B (SDHB) by immunohistochemistry has been used to stratify GIST into an SDHB-retained and an SDHB-deficient group. In this review, we focus on GIST sub-classification based on clinicopathologic, and molecular findings and discuss the known and yet emerging prognostic and predictive genetic alterations. We also give insights into the limitations of targeted therapy and highlight the mechanisms of secondary resistance.

Identification of Wee1 as a target in combination with avapritinib for gastrointestinal stromal tumor treatment

Management of gastrointestinal stromal tumors (GISTs) has been revolutionized by the identification of activating mutations in KIT and PDGFRA and clinical application of RTK inhibitors in advanced disease. Stratification of GISTs into molecularly defined subsets provides insight into clinical behavior and response to approved targeted therapies. Although these RTK inhibitors are effective in most GISTs, resistance remains a significant clinical problem. Development of effective treatment strategies for refractory GISTs requires identification of novel targets to provide additional therapeutic options. Global kinome profiling has the potential to identify critical signaling networks and reveal protein kinases essential in GISTs. Using multiplexed inhibitor beads and mass spectrometry, we explored the majority of the kinome in GIST specimens from the 3 most common molecular subtypes (KIT mutant, PDGFRA mutant, and succinate dehydrogenase deficient) to identify kinase targets. Kinome profiling with loss-of-function assays identified an important role for G₂/M tyrosine kinase, Wee1, in GIST cell survival. In vitro and in vivo studies revealed significant efficacy of MK-1775 (Wee1 inhibitor) in combination with avapritinib in KIT mutant and PDGFRA mutant GIST cell lines as well as notable efficacy of MK-1775 as a monotherapy in the engineered PDGFRA mutant line. These studies provide strong preclinical justification for the use of MK-1775 in GIST.

Avapritinib in advanced gastrointestinal stromal tumor: case series and review of the literature from a tertiary care center in India

The therapeutic landscape in advanced gastrointestinal stromal tumor has evolved. Avapritinib and ripretinib have now been approved by the US FDA for platelet-derived growth factor alpha D842V-mutant and refractory gastrointestinal stromal tumor patients, respectively. Here we report five patients who have been on avapritinib under an expanded access program. Response assessment was available for four patients - a partial response in two patients and stable disease in one, while one patient had progressive disease. Though preliminary results of the VOYAGER trial have shown less activity of avapritinib and no significant difference in progression-free survival when compared with regorafenib, avapritinib may show some clinical benefit in a subset of patients refractory to approved therapies. We share our experience of five cases, with clinical benefit in three. We believe avapritinib should be further evaluated in clinical trials.

Ripretinib in gastrointestinal stromal tumor: the long-awaited step forward

Gastrointestinal stromal tumor (GIST) represents a paradigm for clinically effective targeted inhibition of oncogenic driver mutations in cancer. Five drugs are currently positioned as the standard of care for the treatment of advanced or metastatic GIST patients. This is the result of continuous, deep understanding of KIT and PDGFRA GIST oncogenic drivers as well as the resistance mechanisms associated to tumor progression. However, the complexity of GIST molecular heterogeneity is an evolving field, and critical questions remain open. Specifically, the clinical benefit of approved and/or investigated targeted agents is strikingly modest at advanced stages of the disease when compared with the activity of first-line imatinib. Ripretinib is a novel switch-pocket inhibitor with broad activity against KIT and PDGFRA oncoproteins and has recently demonstrated antitumoral activity across phase I to phase III clinical trials. Therefore, ripretinib has emerged as a new standard of care for advanced, multi-resistant GIST patients. Based on this data, the Food and Drug Administration has granted in 2020 the approval of ripretinib for GIST patients after progression to imatinib, sunitinib and regorafenib. This, in turn, constitutes a major breakthrough in sarcoma drug development, as there have not been new treatment approvals in GIST for nearly a decade. Herein, we provide a critical review on the preclinical and clinical development of ripretinib in GIST. Furthermore, we seek to assess the biological and clinical impact of this new standard of care on the course of the disease, aiming to provide an insight on future treatments strategies for the next coming years.

Gastrointestinal Stromal Tumors (GISTs): Novel Therapeutic Strategies with Immunotherapy and Small Molecules

Gastrointestinal stromal tumors (GISTs) are the most common types of malignant mesenchymal tumors in the gastrointestinal tract, with an estimated incidence of 1.5/100.000 per year and 1–2% of gastrointestinal neoplasms. About 75–80% of patients have mutations in the KIT gene in exons 9, 11, 13, 14, 17, and 5–10% of patients have mutations in the platelet-derived growth factor receptor a (PDGFRA) gene in exons 12, 14, 18. Moreover, 10–15% of patients have no mutations and are classified as wild type GIST. The treatment for metastatic or unresectable GISTs includes imatinib, sunitinib, and regorafenib. So far, GIST therapies have raised great expectations and offered patients a better quality of life, but increased pharmacological resistance to tyrosine kinase inhibitors is often observed. New treatment options have emerged, with ripretinib, avapritinib, and cabozantinib getting approvals for these tumors. Nowadays, immune checkpoint inhibitors form a new landscape in cancer therapeutics and have already shown remarkable responses in various tumors. Studies in melanoma, non-small-cell lung cancer, and renal cell carcinoma are very encouraging as these inhibitors have increased survival rates. The purpose of this review is to present alternative approaches for the treatment of the GIST patients, such as combinations of immunotherapy and novel inhibitors with traditional therapies (tyrosine kinase inhibitors).

The management of metastatic GIST: current standard and investigational therapeutics

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract. The majority of GISTs harbor gain of function mutations in either KIT or PDGFRα. Determination of the GIST molecular subtype upon diagnosis is important because this information informs therapeutic decisions in both the adjuvant and metastatic setting. The management of GIST was revolutionized by the introduction of imatinib, a KIT inhibitor, which has become the standard first line treatment for metastatic GIST. However, despite a clinical benefit rate of 80%, the majority of patients with GIST experience disease progression after 2-3 years of imatinib therapy. Second and third line options include sunitinib and regorafenib, respectively, and yield low response rates and limited clinical benefit. There have been recent FDA approvals for GIST including ripretinib in the fourth-line setting and avapritinib for PDGFRA exon 18-mutant GIST. This article aims to review the optimal treatment approach for the management of patients with advanced GIST. It examines the standard treatment options available but also explores the novel treatment approaches in the setting of imatinib refractory GIST.

Resistance to Avapritinib in PDGFRA-Driven GIST Is Caused by Secondary Mutations in the PDGFRA Kinase Domain

Gastrointestinal stromal tumors (GIST) harboring activating mutations of PDGFRA respond to imatinib, with the notable exception of the most common mutation, D842V. Avapritinib is a novel, potent KIT/PDGFRA inhibitor with substantial clinical activity in patients with the D842V genotype. To date, only a minority of PDGFRA-mutant patients treated with avapritinib have developed secondary resistance. Tumor and plasma biopsies in 6 of 7 patients with PDGFRA primary mutations who progressed on avapritinib or imatinib had secondary resistance mutations within PDGFRA exons 13, 14, and 15 that interfere with avapritinib binding. Secondary PDGFRA mutations causing V658A, N659K, Y676C, and G680R substitutions were found in 2 or more patients each, representing recurrent mechanisms of PDGFRA GIST drug resistance. Notably, most PDGFRA-mutant GISTs refractory to avapritinib remain dependent on the PDGFRA oncogenic signal. Inhibitors that target PDGFRA protein stability or inhibition of PDGFRA-dependent signaling pathways may overcome avapritinib resistance. SIGNIFICANCE: Here, we provide the first description of avapritinib resistance mechanisms in PDGFRA-mutant GIST.This article is highlighted in the In This Issue feature, p. 1.

Tropomyosin receptor kinase inhibitors in the management of sarcomas

PURPOSE OF REVIEW

Genetic aberrations resulting in tropomyosin receptor kinase (TRK) fusion proteins can drive oncogenesis and are postulated to occur in up to 1% of solid tumours. However, TRK fusions in adult sarcomas are rare and there is a significant challenge in identifying patients with sarcomas harbouring TRK fusions in the clinical setting. Despite a recent European Society of Medical Oncology consensus article regarding screening of tumours for TRK fusions, economical and practical limitations present a barrier to widespread screening of sarcomas.

RECENT FINDINGS

Larotrectinib and entrectinib are pan-TRK inhibitors which have both received FDA approval for the management of solid tumours harbouring NTRK fusions. Initial results of a number of clinical trials have demonstrated promising efficacy and safety data, including dramatic and durable responses in patients with sarcomas. As such, TRK inhibitors represent a promising treatment option in a small cohort of adult sarcoma patients, where currently treatment options are limited. The emergence of acquired resistance is a concern associated with TRK inhibitor therapy and a number of second-generation agents targeting TRK kinase mutations driving acquired resistance have entered early-phase clinical trials.

SUMMARY

With the growing appreciation of the implications of TRK fusions, this review will summarize the emerging clinical trial data of TRK inhibitors in sarcomas. Although in their infancy, clinical trial results are encouraging, and as further results and analyses are released, we will have a greater understanding of their impact on clinical practice and the management of patients with sarcomas.

New insights into the clinical management of advanced gastrointestinal stromal tumors

INTRODUCTION

90% of gastrointestinal stromal tumors (GISTs) harbor an activating mutation in the KIT or PDGFRα oncogene, and these are known to confer imatinib sensitivity.

AREAS COVERED

The author reviews the data regarding the current management of GIST, mechanisms of resistance to imatinib, and new drugs currently in clinical development and provides his unique perspectives on the subject matter.

EXPERT OPINION

Several studies have shown that the response to imatinib in GIST patients mainly depends on the mutational status of KIT or PDGFRα. Moreover, most, if not all, patients treated with imatinib for advanced GIST will develop a secondary progressive disease under the treatment. In most cases, such progressions are the result of acquired resistance due to the occurrence of secondary c-KIT mutations, especially in GISTs with primary exon 11 mutations. Sunitinib and regorafenib are inhibitors of multiple tyrosine kinases, including KIT, PDGFRα, PDGFRβ, and VEGFRs, and are approved for the management of imatinib- and imatinib/sunitinib-refractory GIST patients, respectively. Clearly, better knowledge of the molecular mechanisms underlying the resistance to imatinib as well as the development of a new class of broad-spectrum tyrosine kinase inhibitors such as avapritinib and ripretinib will provide new individualized therapeutic strategies for GIST patients.

Systemic therapy of advanced/metastatic gastrointestinal stromal tumors: an update on progress beyond imatinib, sunitinib, and regorafenib

Introduction: Discovery of oncogenic mutations in the KIT and PDGFRA tyrosine kinase receptor was a crucial step for the development of tyrosine kinase inhibitors (TKIs). Since then, GIST became a model for the development of molecular-targeted therapy, which led to dramatically improved median overall survival of advanced GIST. Still, further progress is needed after third-line or for TKI resistant mutations. Areas covered: In this review, after a brief introduction on imatinib, sunitinib, and regorafenib, an overview of TKIs that was evaluated beyond these drugs is provided, with a main focus on the novel approved TKIs. Expert opinion: Combination therapies have thus far not fulfilled their promise in GIST, nor did immunotherapy. Increased understanding of GIST and advances in the development of molecular-targeted drugs led to the introduction of ripretinib and avapritinib. Furthermore, NTRK inhibitors became available for ultrarare NTRK fusions. Solutions for NF1 and BRAF mutated and SDH-deficient GIST are still to be awaited. This all underlines the need for adequate molecular profiling of high-risk GISTs before treatment is started. Possibly by using circulating tumor DNA in the future, targeting resistance mutations with specific drugs along the course of the disease would be easier, avoiding multiple tumor biopsies.

Tyrosine Kinase Receptors in Oncology

Tyrosine kinase receptors (TKR) comprise more than 60 molecules that play an essential role in the molecular pathways, leading to cell survival and differentiation. Consequently, genetic alterations of TKRs may lead to tumorigenesis and, therefore, cancer development. The discovery and improvement of tyrosine kinase inhibitors (TKI) against TKRs have entailed an important step in the knowledge-expansion of tumor physiopathology as well as an improvement in the cancer treatment based on molecular alterations over many tumor types. The purpose of this review is to provide a comprehensive review of the different families of TKRs and their role in the expansion of tumor cells and how TKIs can stop these pathways to tumorigenesis, in combination or not with other therapies. The increasing growth of this landscape is driving us to strengthen the development of precision oncology with clinical trials based on molecular-based therapy over a histology-based one, with promising preliminary results.

Sarcoma treatment in the era of molecular medicine

Sarcomas are heterogeneous and clinically challenging soft tissue and bone cancers. Although constituting only 1% of all human malignancies, sarcomas represent the second most common type of solid tumors in children and adolescents and comprise an important group of secondary malignancies. More than 100 histological subtypes have been characterized to date, and many more are being discovered due to molecular profiling. Owing to their mostly aggressive biological behavior, relative rarity, and occurrence at virtually every anatomical site, many sarcoma subtypes are in particular difficult-to-treat categories. Current multimodal treatment concepts combine surgery, polychemotherapy (with/without local hyperthermia), irradiation, immunotherapy, and/or targeted therapeutics. Recent scientific advancements have enabled a more precise molecular characterization of sarcoma subtypes and revealed novel therapeutic targets and prognostic/predictive biomarkers. This review aims at providing a comprehensive overview of the latest advances in the molecular biology of sarcomas and their effects on clinical oncology; it is meant for a broad readership ranging from novices to experts in the field of sarcoma.

Non-Coding RNAs, a Novel Paradigm for the Management of Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal malignancies found in the gastrointestinal tract. At a molecular level, most GISTs are characterized by gain-of-function mutations in V-Kit Hardy-Zuckerman 4 Feline Sarcoma Viral Oncogene Homolog (KIT) and Platelet Derived Growth Factor Receptor Alpha (PDGFRA), leading to constitutive activated signaling through these receptor tyrosine kinases, which drive GIST pathogenesis. In addition to surgery, treatment with the tyrosine kinase inhibitor imatinib forms the mainstay of GIST treatment, particularly in the advanced setting. Nevertheless, the majority of GISTs develop imatinib resistance. Biomarkers that indicate metastasis, drug resistance and disease progression early on could be of great clinical value. Likewise, novel treatment strategies that overcome resistance mechanisms are equally needed. Non-coding RNAs, particularly microRNAs, can be employed as diagnostic, prognostic or predictive biomarkers and have therapeutic potential. Here we review which non-coding RNAs are deregulated in GISTs, whether they can be linked to specific clinicopathological features and discuss how they can be used to improve the clinical management of GISTs.

Gastrointestinal Stromal Tumor: Challenges and Opportunities for a New Decade

Gastrointestinal stromal tumor (GIST) provides a paradigm to evaluate new molecularly targeted therapies and to identify structural and functional mechanisms for drug response and resistance. Drug development in GIST has successfully exploited the high reliance on KIT/PDGFRA oncogenic signaling as a therapeutic vulnerability. The recent arrival of avapritinib and ripretinib to the GIST arena has aimed to further improve on precision kinase inhibition and address tumor heterogeneity in imatinib-resistant GIST. The two main clinical challenges for the forthcoming years entail tumor eradication in patients with early-stage GIST, and maximization of tumor response in late-stage disease. To succeed, we will need to better understand the mechanisms behind adaptation to KIT inhibition and apoptosis evasion, tumor evolution after successive lines of treatment, and to explore clinically novel creative therapeutic strategies, with the overarching goal to tackle the intrinsic oncogenic complexity while minimizing adverse events.

Avapritinib in the treatment of PDGFRA exon 18 mutated gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GIST) can be molecularly classified based on different subtypes including mutations in KIT and PDGFRA. Patients with PDGFRA mutations are an important subgroup that commonly arise in the stomach and are associated with a more indolent disease course. Importantly, the most common PDGFRA molecular subtype, the D842V mutation in exon 18 of the gene which alters the activation loop, is imatinib insensitive in in vitro studies. Poor responses to imatinib have been seen clinically compared with PDGFRA exon 18 non-D842V-mutated GIST. Avapritinib (BLU-285) is a potent KIT and PDGFRA-specific tyrosine kinase inhibitor which has shown >90% response rates in patients with PDGFRA exon 18 D842V-mutated GIST. Results from the Phase I trial of avapritinib have indicated that this drug should be the standard of care for patients with PDGFRA exon 18 D842V-mutated GIST.

Revolutions in treatment options in gastrointestinal stromal tumours (GISTs): the latest updates

OPINION STATEMENT

The treatment of advanced GIST is rapidly evolving with the development of novel molecular compounds such as avapritinib and ripretinib, but also promising results have been achieved with cabozantinib in a phase II trial. The availability of over five lines of treatment for patients with advanced GIST is likely to completely shift the current second-line and third-line treatment options, and will also potentially enable a personalised approach to treatment. Imatinib will most likely remain as the first-line treatment of choice for the vast majority of GIST patients. However, for GIST patients with tumours harbouring a D842V mutation in PDGFRA exon 18, avapritinib has shown efficacy and will become first-line therapy for this molecular subgroup. For second- and third-line treatment, results are awaited of a number of clinical trials. However, second-line and further treatment could potentially be tailored depending on secondary mutations found in imatinib-resistant GISTs. As secondary resistance to TKIs remains the biggest challenge in the treatment of GIST and despite negative results with alternating regimens in phase II, combination treatments should be further evaluated to tackle this issue. Moreover, the favourable safety profiles observed with avapritinib and ripretinib suggest that combination treatments are feasible, for instance, combining two TKIs or a TKI with drugs targeting downstream signalling pathways, such as PI3K inhibitors or MEK inhibitors. Finally, in line with further personalisation of treatment in GIST, a multidisciplinary approach is essential, and local treatment options, such as RFA, resection in case of unifocal progression, and radiotherapy, should be considered.