Diagnosis and management of tropomyosin receptor kinase (TRK) fusion sarcomas: expert recommendations from the World Sarcoma Network.

Sarcomas are a heterogeneous group of malignancies with mesenchymal lineage differentiation. The discovery of neurotrophic tyrosine receptor kinase (NTRK) gene fusions as tissue-agnostic oncogenic drivers has led to new personalized therapies for a subset of patients with sarcoma in the form of tropomyosin receptor kinase (TRK) inhibitors. NTRK gene rearrangements and fusion transcripts can be detected with different molecular pathology techniques, while TRK protein expression can be demonstrated with immunohistochemistry. The rarity and diagnostic complexity of NTRK gene fusions raise a number of questions and challenges for clinicians. To address these challenges, the World Sarcoma Network convened two meetings of expert adult oncologists and pathologists and subsequently developed this article to provide practical guidance on the management of patients with sarcoma harboring NTRK gene fusions. We propose a diagnostic strategy that considers disease stage and histologic and molecular subtypes to facilitate routine testing for TRK expression and subsequent testing for NTRK gene fusions.

Efficacy and tolerability of trabectedin in elderly patients with sarcoma: subgroup analysis from a phase III, randomized controlled study of trabectedin or dacarbazine in patients with advanced liposarcoma or leiomyosarcoma.

Background: Treatment options for soft tissue sarcoma (STS) patients aged ≥65 years (elderly) can be limited by concerns regarding the increased risk of toxicity associated with standard systemic therapies. Trabectedin has demonstrated improved disease control in a phase III trial (ET743-SAR-3007) of patients with advanced liposarcoma or leiomyosarcoma after failure of anthracycline-based chemotherapy. Since previous retrospective analyses have suggested that trabectedin has similar safety and efficacy outcomes regardless of patient age, we carried out a subgroup analysis of the safety and efficacy observed in elderly patients enrolled in this trial. Patients and methods: Patients were randomized 2 : 1 to trabectedin (n = 384) or dacarbazine (n = 193) administered intravenously every-3-weeks. The primary end point was overall survival (OS); secondary end points were progression-free survival (PFS), time-to-progression, objective response rate (ORR), duration of response, symptom severity, and safety. A post hoc analysis was conducted in the elderly patient subgroup. Results: Among 131 (trabectedin = 94; dacarbazine = 37) elderly patients, disease characteristics were well-balanced and consistent with those of the total study population. Treatment exposure was longer in patients treated with trabectedin versus dacarbazine (median four versus two cycles, respectively), with a significantly higher proportion receiving prolonged therapy (≥6 cycles) in the trabectedin arm (43% versus 23%, respectively; P = 0.04). Elderly patients treated with trabectedin showed significantly improved PFS [4.9 versus 1.5 months, respectively; hazard ratio (HR)=0.40; P = 0.0002] but no statistically significant improvement in OS (15.1 versus 8.0 months, respectively; HR = 0.72; P = 0.18) or ORR (9% versus 3%, respectively; P = 0.43). The safety profile for elderly trabectedin-treated patients was comparable to that of the overall trabectedin-treated study population. Conclusions: This subgroup analysis of the elderly population of ET743-SAR-3007 suggests that elderly patients with STS and good performance status can expect clinical benefit from trabectedin similar to that observed in younger patients. Trial registration: www.clinicaltrials.gov, NCT01343277.

Long-term follow-up results of the multicenter phase II trial of regorafenib in patients with metastatic and/or unresectable GI stromal tumor after failure of standard tyrosine kinase inhibitor therapy.

BACKGROUND: This investigator-initiated trial provided the justification for the phase III GRID study resulting in worldwide regulatory approval of regorafenib as a third-line therapy for patients with metastatic gastrointestinal stromal tumors (GIST). We report the genotype analyses, long-term safety, and activity results from this initial trial of regorafenib in GIST. PATIENTS AND METHODS: The trial was conducted between February 2010 and January 2014, among adult patients with metastatic GIST, after failure of at least imatinib and sunitinib. Patients received regorafenib orally, 160 mg once daily, days 1-21 of a 28-day cycle. Clinical benefit rate (CBR), defined as complete or partial response (PR), or stable disease lasting ≥16 weeks per RECIST 1.1, progression-free survival (PFS), overall survival (OS), long-term safety data, and metabolic response by functional imaging were assessed. RESULTS: Thirty-three patients received at least one dose of regorafenib. The median follow-up was 41 months. CBR was documented in 25 of 33 patients [76%; 95% confidence interval (CI) 58% to 89%], including six PRs. The median PFS was 13.2 months (95% CI 9.2-18.3 months) including four patients who remained progression-free at study closure, each achieving clinical benefit for more than 3 years (range 36.8-43.5 months). The median OS was 25 months (95% CI 13.2-39.1 months). Patients whose tumors harbored a KIT exon 11 mutation demonstrated the longest median PFS (13.4 months), whereas patients with KIT/PDGFRA wild-type, non-SDH-deficient tumors experienced a median 1.6 months PFS (P < 0.0001). Long-term safety profile is consistent with previous reports; hand-foot skin reaction and hypertension were the most common reasons for dose reduction. Notably, regorafenib induced objective responses and durable benefit in SDH-deficient GIST. CONCLUSIONS: Long-term follow-up of patients with metastatic GIST treated with regorafenib suggests particular benefit among patients with primary KIT exon 11 mutations and those with SDH-deficient GIST. Dose modifications are frequently required to manage treatment-related toxicities. CLINICAL TRIAL NUMBER: NCT01068769.

Genome-wide functional screening identifies CDC37 as a crucial HSP90-cofactor for KIT oncogenic expression in gastrointestinal stromal tumors.

Most gastrointestinal stromal tumors (GISTs) contain KIT or PDGFRA kinase gain-of-function mutations, and therefore respond clinically to imatinib and other tyrosine kinase inhibitor (TKI) therapies. However, clinical progression subsequently results from selection of TKI-resistant clones, typically containing secondary mutations in the KIT kinase domain, which can be heterogeneous between and within GIST metastases in a given patient. TKI-resistant KIT oncoproteins require HSP90 chaperoning and are potently inactivated by HSP90 inhibitors, but clinical applications in GIST patients are constrained by the toxicity resulting from concomitant inactivation of various other HSP90 client proteins, beyond KIT and PDGFRA. To identify novel targets responsible for KIT oncoprotein function, we performed parallel genome-scale short hairpin RNA (shRNA)-mediated gene knockdowns in KIT-mutant GIST-T1 and GIST882. GIST cells were infected with a lentiviral shRNA pooled library targeting 11 194 human genes, and allowed to proliferate for 5-7 weeks, at which point assessment of relative hairpin abundance identified the HSP90 cofactor, CDC37, as one of the top six GIST-specific essential genes. Validations in treatment-naive (GIST-T1, GIST882) vs imatinib-resistant GISTs (GIST48, GIST430) demonstrated that: (1) CDC37 interacts with oncogenic KIT; (2) CDC37 regulates expression and activation of KIT and downstream signaling intermediates in GIST; and (3) unlike direct HSP90 inhibition, CDC37 knockdown accomplishes prolonged KIT inhibition (>20 days) in GIST. These studies highlight CDC37 as a key biologic vulnerability in both imatinib-sensitive and imatinib-resistant GIST. CDC37 targeting is expected to be selective for KIT/PDGFRA and a subset of other HSP90 clients, and thereby represents a promising strategy for inactivating the myriad KIT/PDGFRA oncoproteins in TKI-resistant GIST patients.

A multicenter phase II study of pazopanib in patients with advanced gastrointestinal stromal tumors (GIST) following failure of at least imatinib and sunitinib.

BACKGROUND: Advanced GISTs are incurable, but often treatable for years with tyrosine kinase inhibitors (TKIs). The majority of GISTs harbor an oncogenic activating mutation in KIT or PDGFRA. Inhibition of this activating mutation with TKIs most often leads to durable disease control for many patients. However, almost all patients develop resistance to these TKIs, typically due to the development of secondary mutations, heralding the need for new therapeutic options. We conducted a phase II study evaluating the efficacy and toxicity of pazopanib, a broad spectrum TKI inhibiting KIT, VEGFRs (-1, -2, and -3), and PDGFR (-α and-ß) in patients with advanced GIST following failure of at least imatinib and sunitinib. METHODS: Patients received pazopanib 800 mg orally once daily. All patients were assessed for efficacy with CT scans every 8 weeks (two cycles). Patients continued pazopanib until progression or unacceptable toxicity. The primary end point was the 24-week nonprogression [complete response+partial response+stable disease (SD)] rate (NPR) per RECIST 1.1. Secondary end points included PFS, OS, and toxicity. RESULTS: Between August 2011 and September 2012, a total of 25 patients were treated at two institutions. Median number of prior therapy was 3 (range 2-7). A total of 90 cycles of pazopanib were administered, with a median of two cycles (range 1 to 17+) per patient. Best response of SD at any time was observed in 12 (48%) patients. The NPR was 17% [95% confidence interval (CI) 4.5-37]. All but one patient discontinued protocol either due to PD (n = 19) or intolerance (n = 4). One patient with succinate dehydrogenase (SDH)-deficient GIST exhibited continuing disease control after 17 cycles. The median PFS for the entire cohort was 1.9 months (95% CI 1.6-5.2), and the median OS was 10.7 months (95% CI 3.9-NR). CONCLUSIONS: Pazopanib was reasonably well tolerated with no unexpected toxicities. Pazopanib as a single agent has marginal activity in unselected heavily pretreated patients with advanced GIST.

Trabectedin is a feasible treatment for soft tissue sarcoma patients regardless of patient age: a retrospective pooled analysis of five phase II trials.

BACKGROUND: This retrospective pooled analysis assessed the effect of age on the efficacy and safety of trabectedin in young and elderly patients with recurrent advanced soft tissue sarcoma (STS). METHODS: Data from 350 adults with STS treated in five phase II trials with trabectedin were divided in the younger (<60 years; n=267) and the older cohort (≥60 years; n=83). RESULTS: The response rate did not differ with age (younger: 10.1% vs elderly 9.6%). No significant differences were found in median progression-free survival (PFS) in younger (2.5 months) and older (3.7 months) cohort with a comparable PFS rates at 3 (45.1% vs 55.1%) and 6 months (29.5% vs 36.4%). Similar median overall survival was observed in both cohorts (13.0 vs 14.0 months). Reversible neutropenia and aspartate aminotransferase/alanine aminotransferase elevation were the most common abnormalities. A higher incidence of grade 3/4 neutropenia (43.6% vs 60.2%) and fatigue (6.3% vs 14.4%) was observed in older patients. In 24 patients aged ≥70 years, no significant differences in efficacy or safety outcomes were found. CONCLUSION: This analysis demonstrated that trabectedin is a feasible treatment in young and elderly patients with STS, with meaningful clinical benefits and an acceptable safety profile, essential in palliative treatment of elderly patients.

Clinical outcomes and safety with trabectedin therapy in patients with advanced soft tissue sarcomas following failure of prior chemotherapy: results of a worldwide expanded access program study.

BACKGROUND: This expanded access program (EAP) was designed to provide trabectedin access for patients with incurable soft tissue sarcoma (STS) following progression of disease with standard therapy. The outcomes of trial participants accrued over approximately 5 years are reported. PATIENTS AND METHODS: Adult patients with advanced STS of multiple histologies, including leiomyosarcoma and liposarcoma (L-sarcomas), following relapse or disease progression following standard-of-care chemotherapy, were enrolled. Trabectedin treatment cycles (1.5 mg/m(2), intravenously over 24 h) were repeated q21 days. Objective response, overall survival (OS), and safety were evaluated. RESULTS: Of 1895 patients enrolled, 807 (43%) had evaluable objective response data, with stable disease reported in 343 (43%) as best response. L-sarcoma patients exhibited longer, OS compared with other histologies [16.2 months (95% confidence interval (CI) 14.1-19.5) versus 8.4 months (95% CI 7.1-10.7)], and a slightly higher objective response rate [6.9% (95% CI 4.8-9.6) versus 4.0% (95% CI 2.1-6.8)]. The median treatment duration was 70 days representing a median of three treatment cycles; 30% of patients received ≥ 6 cycles. Safety and tolerability in this EAP were consistent with prior clinical trial data. CONCLUSION: Results of this EAP are consistent with previous reports of trabectedin, demonstrating disease control despite a low incidence of objective responses in advanced STS patients after failure of standard chemotherapy. CLINICALTRIALS.GOV: NCT00210665.

Growth modulation index as metric of clinical benefit assessment among advanced soft tissue sarcoma patients receiving trabectedin as a salvage therapy.

BACKGROUND: The growth modulation index (GMI) is the ratio of time to progression with the nth line (TTP(n)) of therapy to the TTP(n)(-1) with the n-1th line. GMI >1.33 is considered as a sign of activity in phase II trials. PATIENTS AND METHODS: This retrospective analysis evaluated the concordance between the GMI and the efficacy outcomes in 279 patients with advanced soft tissue sarcoma (ASTS) treated with trabectedin 1.5 mg/m² (24-h infusion every 3 weeks) in four phase II trials. RESULTS: One hundred and forty-two (51%) patients received one prior line and 137 ≥ 2 lines. The median TTP(n) was 2.8 months (range 0.2-26.8), whereas the median TTP(n)(-1) was 4.0 months (0.3-79.5). The median GMI was 0.6 (0.0-14.4). Overall, 177 patients (63%) had a GMI <1; 21 (8%) a GMI equal to 1-1.33 and 81 (29%) a GMI >1.33, which correlated with the median overall survival in those patients (9.1, 13.9 and 23.8 months, respectively, P = 0.0005). A high concordance rate between the GMI and response rate (P < 0.0001) and progression-free survival (PFS, P < 0.0001) was observed. Good performance status (PS) was the only factor associated with GMI >1.33 (PS = 0; P < 0.04). CONCLUSIONS: A high GMI was associated with favorable efficacy outcomes in patients treated with trabectedin. Further research is needed to assess GMI as an indicator in this setting.

Hypertension as a potential biomarker of efficacy in patients with gastrointestinal stromal tumor treated with sunitinib.

BACKGROUND: Reliable biomarkers of sunitinib response in gastrointestinal stromal tumor (GIST) are lacking. Hypertension (HTN), an on-target class effect of vascular endothelial growth factor signaling-pathway inhibitors, has been shown to correlate with clinical outcome in advanced renal cell carcinoma treated with sunitinib. PATIENTS AND METHODS: This retrospective analysis examined correlations between sunitinib-associated HTN and antitumor efficacy (N = 319) and safety (N = 1565) across three advanced GIST studies. Blood pressure (BP) was measured on days 1 and 28 of each treatment cycle at a minimum. Time-to-event endpoints were estimated using Kaplan-Meier methods, and patient subgroups with and without HTN (maximum systolic BP ≥ 140 mmHg and/or diastolic BP ≥ 90 mmHg) were compared using Cox proportional hazards models. Landmark analyses evaluated associations between early HTN and efficacy endpoints. Adverse events (AEs) were compared between groups. RESULTS: Sunitinib-associated HTN correlated with improved objective response rates, time to tumor progression, progression-free survival, and overall survival. Almost all benefits remained significant in multivariate and landmark analyses. Overall incidences of HTN-related AEs were low and similar between groups; incidences of cardiovascular AEs were somewhat higher in patients with HTN. CONCLUSION: Sunitinib-associated HTN appeared to correlate with improved clinical outcomes in GIST, while incidences of HTN-associated AEs were generally low and manageable.

Phase III study of nilotinib versus best supportive care with or without a TKI in patients with gastrointestinal stromal tumors resistant to or intolerant of imatinib and sunitinib.

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

Phase II clinical trial of neoadjuvant trabectedin in patients with advanced localized myxoid liposarcoma.

BACKGROUND: To evaluate neoadjuvant trabectedin (1.5 mg/m(2) 24-h i.v. infusion every 3 weeks; three to six cycles) in patients with locally advanced myoxid liposarcoma (ML) previously untreated with chemotherapy or radiation. PATIENTS AND METHODS: Primary efficacy end point was pathological complete response (pCR) or tumoral regression rate. Objective response according to RECIST (v.1.0) was a secondary end point. RESULTS: Three of 23 assessable patients had pCR [13%; 95% confidence interval (CI), 3% to 34%]. Furthermore, very good and moderate histological responses were observed in another 2 and 10 patients, respectively. Histological decrement in the cellular and vascular tumor component and maturation of tumor cells to lipoblasts were observed in both myoxid and myoxid/round cell variants. Seven patients had partial response according to RECIST (objective response rate of 24%; 95% CI, 10% to 44%). No disease progression was reported. Neoadjuvant trabectedin was usually well tolerated, with a safety profile similar to that described in patients with soft tissue sarcoma or other tumor types. CONCLUSION: Trabectedin 1.5 mg/m(2) given as a 24-h i.v. infusion every 3 weeks is a therapeutic option in the neoadjuvant setting of ML.

A phase I-II study of everolimus (RAD001) in combination with imatinib in patients with imatinib-resistant gastrointestinal stromal tumors.

BACKGROUND: Imatinib is standard therapy for advanced gastrointestinal stromal tumors (GIST), but most patients develop resistance. This phase I-II study assessed the safety and efficacy of co-administering everolimus with imatinib in imatinib-resistant GIST. PATIENTS AND METHODS: In phase I, patients received imatinib (600/800 mg/day) combined with weekly (20 mg) or daily (2.5/5.0 mg) everolimus to determine the optimal dose. In phase II, patients were divided into two strata (progression on imatinib only; progression after imatinib and sunitinib/other tyrosine kinase inhibitor) and received everolimus 2.5 mg plus imatinib 600 mg/day. Primary end point was 4-month progression-free survival (PFS). RESULTS: Combination treatment was well tolerated. Common adverse events were diarrhea, nausea, fatigue, and anemia. In phase II strata 1 and 2, 4 of 23 (17%) and 13 of 35 (37%) assessable patients, respectively, were progression free at 4 months; median PFS was 1.9 and 3.5 months, and median overall survival was 14.9 and 10.7 months, respectively. In stratum 1, 36% had stable disease (SD) and 54% progressive disease (PD), while in stratum 2, 2% had partial response, 43% SD, and 32% PD. CONCLUSION: Predetermined efficacy criteria were met in both strata. The combination of everolimus and imatinib after failure on imatinib and sunitinib merits further investigation in GIST.

Clinical evaluation of continuous daily dosing of sunitinib malate in patients with advanced gastrointestinal stromal tumour after imatinib failure.

AIMS: To assess the antitumour activity, safety, pharmacokinetics and pharmacodynamics of continuous daily sunitinib dosing in patients with imatinib-resistant/intolerant gastrointestinal stromal tumour (GIST) and to assess morning dosing versus evening dosing. PATIENTS AND METHODS: In this open-label phase II study, patients were randomised to receive morning or evening dosing of sunitinib 37.5mg/day. The primary end-point was clinical benefit rate (CBR; percent complete responses+partial responses [PRs]+stable disease [SD] 24 weeks). Secondary end-points included progression-free survival (PFS), overall survival (OS), safety, pharmacokinetic parameters and plasma biomarker levels. RESULTS: Sixty of 61 planned patients received treatment (30 per dosing group); 26 completed the study. Overall, the CBR was 53% (95% exact CI, 40-66): eight patients (13%) achieved objective PRs; 24 (40%) achieved SD 24 weeks. Median PFS was 34 weeks (95% CI, 24-49); median OS was 107 weeks (95% CI, 72 - not yet calculable). Most adverse events (AEs) were of grade 1 or 2 in severity, and were manageable through dose modification or standard interventions. No new AEs were apparent compared with the approved intermittent dosing schedule. Antitumour activity and safety were generally similar with morning and evening dosing. Continuous daily sunitinib dosing achieved and sustained effective drug concentrations without additional accumulation across cycles. Decreases from baseline in plasma levels of soluble KIT after 20 and 24 weeks of dosing correlated with longer OS. CONCLUSION: For patients with imatinib-resistant/intolerant GIST, continuous daily sunitinib dosing appears to be an active alternative dosing strategy with acceptable safety.

Heterogeneity of kinase inhibitor resistance mechanisms in GIST.

Most GIST patients develop clinical resistance to KIT/PDGFRA tyrosine kinase inhibitors (TKI). However, it is unclear whether clinical resistance results from single or multiple molecular mechanisms in each patient. KIT and PDGFRA mutations were evaluated in 53 GIST metastases obtained from 14 patients who underwent surgical debulking after progression on imatinib or sunitinib. To interrogate possible resistance mechanisms across a broad biological spectrum of GISTs, inter- and intra-lesional heterogeneity of molecular drug-resistance mechanisms were evaluated in the following: conventional KIT (CD117)-positive GISTs with KIT mutations in exon 9, 11 or 13; KIT-negative GISTs; GISTs with unusual morphology; and KIT/PDGFRA wild-type GISTs. Genomic KIT and PDGFRA mutations were characterized systematically, using complementary techniques including D-HPLC for KIT exons 9, 11-18 and PDGFRA exons 12, 14, 18, and mutation-specific PCR (V654A, D820G, N822K, Y823D). Primary KIT oncogenic mutations were found in 11/14 patients (79%). Of these, 9/11 (83%), had secondary drug-resistant KIT mutations, including six (67%) with two to five different secondary mutations in separate metastases, and three (34%) with two secondary KIT mutations in the same metastasis. The secondary mutations clustered in the KIT ATP binding pocket and kinase catalytic regions. FISH analyses revealed KIT amplicons in 2/10 metastases lacking secondary KIT mutations. This study demonstrates extensive intra- and inter-lesional heterogeneity of resistance mutations and gene amplification in patients with clinically progressing GIST. KIT kinase resistance mutations were not found in KIT/PDGFRA wild-type GISTs or in KIT-mutant GISTs showing unusual morphology and/or loss of KIT expression by IHC, indicating that resistance mechanisms are fundamentally different in these tumours. Our observations underscore the heterogeneity of clinical TKI resistance, and highlight the therapeutic challenges involved in salvaging patients after clinical progression on TKI monotherapies.

Protein kinase C-theta regulates KIT expression and proliferation in gastrointestinal stromal tumors.

Oncogenic KIT or PDGFRA receptor tyrosine kinase mutations are compelling therapeutic targets in gastrointestinal stromal tumors (GISTs), and the KIT/PDGFRA kinase inhibitor, imatinib, is standard of care for patients with metastatic GIST. However, most of these patients eventually develop clinical resistance to imatinib and other KIT/PDGFRA kinase inhibitors and there is an urgent need to identify novel therapeutic strategies. We reported previously that protein kinase C-theta (PKCtheta) is activated in GIST, irrespective of KIT or PDGFRA mutational status, and is expressed at levels unprecedented in other mesenchymal tumors, therefore serving as a diagnostic marker of GIST. Herein, we characterize biological functions of PKCtheta in imatinib-sensitive and imatinib-resistant GISTs, showing that lentivirus-mediated PKCtheta knockdown is accompanied by inhibition of KIT expression in three KIT+/PKCtheta+ GIST cell lines, but not in a comparator KIT+/PKCtheta- Ewing's sarcoma cell line. PKCtheta knockdown in the KIT+ GISTs was associated with inhibition of the phosphatidylinositol-3-kinase/AKT signaling pathway, upregulation of the cyclin-dependent kinase inhibitors p21 and p27, antiproliferative effects due to G(1) arrest and induction of apoptosis, comparable to the effects seen after direct knockdown of KIT expression by KIT short-hairpin RNA. These novel findings highlight that PKCtheta warrants clinical evaluation as a potential therapeutic target in GISTs, including those cases containing mutations that confer resistance to KIT/PDGFRA kinase inhibitors.

KIT oncogenic signaling mechanisms in imatinib-resistant gastrointestinal stromal tumor: PI3-kinase/AKT is a crucial survival pathway.

Most gastrointestinal stromal tumor (GIST) patients respond to KIT inhibition with imatinib, yet will eventually exhibit resistance. Imatinib-resistance mechanisms are heterogeneous, and little is known about KIT functional roles in imatinib-resistant GIST. Biological consequences of biochemical inhibition of KIT, phosphatidyl-inositol-3-kinase (PI3-K), PLCgamma, MAPK/ERK kinase/mitogen-activated protein kinase (MEK/MAPK), mammalian target of rapamycin (mTOR) and JAK were determined by immunoblotting for protein activation, and by cell proliferation and apoptosis assays in GIST cell lines from imatinib-sensitive GIST (GIST882), imatinib-resistant GISTs (GIST430 and GIST48) and KIT-negative GIST (GIST62). KIT activation was 3- to 6-fold higher in GIST430 and GIST48 than in GIST882, whereas total KIT expression was comparable in these three GIST lines. In addition to the higher set point for KIT activation, GIST430 and GIST48 had intrinsic imatinib resistance. After treatment with 1 muM imatinib, residual KIT activation was 6- and 2.8-fold higher in GIST430 and GIST48, respectively, compared to GIST882. In all GIST lines, cell growth arrest resulted from PI3-K inhibition, and - to a lesser extent - from MEK/MAPK and mTOR inhibition. Inhibition of JAK/STAT or PLCgamma did not affect cell proliferation. Similarly, only PI3-K inhibition resulted in substantial apoptosis in the imatinib-resistant GISTs. We conclude that GIST secondary KIT mutations can be associated with KIT hyperactivation and imatinib resistance. Targeting critical downstream signaling proteins, such as PI3-K, is a promising therapeutic strategy in imatinib-resistant GISTs.

KIT oncoprotein interactions in gastrointestinal stromal tumors: therapeutic relevance.

Most gastrointestinal stromal tumors (GISTs) express oncogenic and constitutively active forms of the KIT or platelet-derived growth factor receptor alpha (PDGFRA) receptor tyrosine kinase proteins, and these kinase oncoproteins serve as targets for effective therapies. Given that mutant KIT oncoproteins serve crucial transforming roles in GISTs, we evaluated interactions with the KIT oncoproteins and determined signaling pathways that are dependent on KIT oncogenic activation in GISTs. Tyrosine-phosphorylated KIT oncoproteins interacted with PDGFRA, PDGFRB, phosphatidylinositol 3-kinase (PI3-K) and PKCtheta in GIST cells, and these interactions were abolished by KIT inhibition with imatinib or PKC412 or KIT RNAi. Notably, tyrosine-phosphorylated PDGFRA was prominent in frozen GIST tumors expressing KIT oncoproteins, suggesting that KIT-mediated PDGFRA phosphorylation is an efficient and biologically consequential mechanism in GISTs. Activated signaling intermediates were identified by immunoaffinity purification of tyrosine-phosphorylated proteins in GIST cells before and after treatment with KIT inhibitors, and these analyses show that GRB2, SHC, CBL and MAPK activation are largely KIT dependent in GISTs, whereas PI3-K, STAT1 and STAT3 activation are partially KIT dependent. In addition, we found that phosphorylation of several tyrosine kinase proteins - including JAK1 and EPHA4 - did not depend on KIT activation. Likewise, paxillin activation was independent of the KIT oncogenic signal. These studies identify signaling pathways that can provide both KIT-dependent and KIT-independent therapeutic synergies in GIST, and thereby highlight clinical strategies that might consolidate GIST therapeutic response to KIT/PDGFRA inhibition.

Ecteinascidin-743 (ET-743) for chemotherapy-naive patients with advanced soft tissue sarcomas: multicenter phase II and pharmacokinetic study.

PURPOSE: To evaluate the response rate, toxicity profile, and pharmacokinetics of ecteinascidin-743 (ET-743) as first-line therapy in patients with unresectable advanced soft tissue sarcoma (STS). PATIENTS AND METHODS: Thirty-six patients with STS were enrolled onto the study between September 1999 and August 2000. Patients were treated with 1.5 mg/m2 of ET-743 given as a 24-hour continuous intravenous (IV) infusion every 21 days. Pharmacokinetic sampling was performed in 23 patients. RESULTS: One complete and five partial responses were achieved in 35 assessable patients for an overall response rate of 17.1% (95% CI, 6.6% to 33.6%). In addition, one patient had a minor response, leading to an overall clinical benefit of 20%. Neutropenia and transaminitis were the main grade 3 to 4 toxicities, which occurred in 33% and 36% of the patients. The estimated 1-year progression-free and overall survival rates were 21% (95% CI, 11% to 41%) and 72% (95% CI, 59% to 88%), respectively. Total body clearance (L/h) was not significantly correlated with body-surface area (r = -0.28; P = .21). Mild hepatic impairment or the extent of prior cytotoxic therapy does not seem to contribute significantly to the high interpatient variability (49%) in the clearance of this drug. Severity of treatment-related toxicity was not correlated with pharmacokinetic variables. CONCLUSION: ET-743 demonstrates clinical activity as first-line therapy against STS with acceptable toxicity. Additional studies to establish empirical dosing guidelines may be necessary to improve the safety of the drug in patients with varying degrees of hepatic dysfunction and definitively establish the role of ET-743 for patients with these malignancies.

Consensus meeting for the management of gastrointestinal stromal tumors. Report of the GIST Consensus Conference of 20-21 March 2004, under the auspices of ESMO.

BACKGROUND: The management of gastrointestinal stromal tumors (GIST) has evolved very rapidly in the last 4 years. The objectives of this international consensus meeting were to describe the optimal management procedures for patients with GIST in localized and advanced stages, as well as research issues for the future. MATERIALS AND METHODS: A panel of experts from six specialties, including pathology, molecular biology, imaging, surgery, medical oncology and methodologists for clinical practice guidelines from different European and extra European sarcoma societies were invited to a 2-day workshop. Several questions were selected by the organizing committee prior to the conference. Selected panelists reviewed the current levels of evidence for each point, and presented their conclusions during the meeting. These proposals were discussed, and consensus points were identified and categorized according to the Standard Options Recommandations (SOR) of the French Federation of Cancer Centers and National Comprehensive Cancer Network (NCCN). RESULTS: Thirty-two consensus points were identified, most from categories 2A of the NCCN and B2 of the SOR. Among these, the standard histological examination with immunohistochemical analysis using CD117, CD34, PS100, desmin and smooth muscle actin is considered standard. Molecular biology for the identification of KIT and PDGFRA mutation is an optional diagnostic procedure for GIST with negative CD117 staining, and otherwise is considered a research procedure. Complete tumor resection with negative tumor margins is the standard surgical treatment. Adjuvant imatinib after optimal tumor resection as well as neo-adjuvant imatinib remain experimental approaches to be performed within prospective clinical studies. Imatinib should be started at the date of diagnosis of metastatic relapse and given until development of intolerance or progressive disease. The optimal criteria for tumor response to imatinib remain to be delineated, and should include not only tumor size reduction or disease stabilization, but also reduction of tumor density (Hounsfield Units) on computed tomography and metabolic activity (i.e. reduction of FDG uptake on positron emission tomography). In a substantial proportion of patients, stable disease and even increase in tumor size may be associated with pathologic response to imatinib therapy, and available survival data indicate that the survival of these patients is similar to that of patients with conventional tumor response. Metastasis resection is an experimental procedure. CONCLUSIONS: Consensus points in clinical management of GIST as well as questions for future clinical trials were identified during this consensus conference on GIST management.

Neo-adjuvant chemotherapy for primary high-grade extremity soft tissue sarcoma.

BACKGROUND: The purpose of this study was to retrospectively analyze the relationship between neo-adjuvant chemotherapy (NAC) and outcome in patients with high-grade extremity sarcomas. PATIENTS AND METHODS: Inclusion criteria were high-grade, deep, >5 cm extremity soft tissue sarcomas. Patients diagnosed between 1990 and 2001 were treated with surgery only (n=282) or NAC containing doxorubicin/ifosfamide/mesna (AIM) (n=74). The stratified Cox proportional hazards model was used to test the effect of NAC on disease-specific survival and recurrence while adjusting for known prognostic factors. RESULTS: NAC was associated with improved disease-specific survival for this cohort of patients (P=0.02). This overall improvement appears to be driven by the benefit of NAC on disease-specific survival for patient with tumors >10 cm. The 3-year disease-specific survival for tumors >10 cm was 0.62 (95% CI: 0.53-0.71) for patients not receiving NAC and 0.83 (95% CI: 0.72-0.95) for patients receiving NAC. CONCLUSION: NAC with AIM was associated with a significant improvement in disease-specific survival in patients with high-grade extremity soft tissue sarcomas >10 cm. These data emphasize the need for further prospective clinical studies of neo-adjuvant or adjuvant chemotherapy for patients with large high-grade extremity sarcomas.