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Background Sinusoidal obstruction syndrome (SOS) due to chemotherapy can cause severe hepatotoxicity, leading to impaired outcome in patients with colorectal cancer. A previous study introduced gadoxetic acid-enhanced magnetic resonance imaging (Gd-EOB-MRI) to diagnose SOS. Purpose To assess the reproducibility of Gd-EOB-MRI-based SOS diagnosis and its relationship with response to chemotherapy and long-term outcome. Material and Methods Twenty-six Gd-EOB-MRI scans of patients undergoing chemotherapy for colorectal liver metastases (CRLM) were retrospectively analyzed. Three radiologists, blinded to clinical data, independently scored presence and severity of SOS on a 5-point scale (0, definitely not present to 4, definitely present). Patients with a score ≥3 were considered SOS+. Inter-observer agreement between readers was assessed with kappa statistics. Response (RECIST 1.1.), occurrence of new CRLM during follow-up (hepatic progression) and overall survival (OS) were compared between patients with and without SOS. Results The inter-observer agreement of SOS scores was poor, with quadratic kappas of 0.17–0.40. For the binary outcome of SOS+ (confidence level [CL] 3–4) vs. SOS– (CL 0–2) agreement was poor, with kappas of 0.03–0.37. Median follow-up was 24 months (range 4–44 months). Response and OS between patients with and without SOS did not differ significantly for any of the readers. Conclusion Inter-observer agreement for the diagnosis of SOS on Gd-EOB-MRI is poor. No significant correlation with relevant outcomes was found for any of the readers. Therefore, MRI for SOS diagnosis might be less useful than previously reported. Other techniques should be explored to accurately diagnose SOS in absence of histological confirmation.

Purpose: Patients, platelet-derived growth factor receptor alpha (PDGFRA) D842V-mutated gastrointestinal stromal tumours (GISTs) are known for their insensitivity to imatinib. However, in clinical practice responses have been observed in some patients. We describe the natural history and treatment outcomes in a cohort of PDGFRA exon 18 mutated GIST patients.Patients and methods: A retrospective cohort study was conducted in PDGFRA exon 18 mutation GIST patients treated in six expert centres in the Netherlands and the United States. Two independent radiologists assessed radiological response to imatinib according to Choi's criteria in all patients with measurable disease treated with imatinib in neo-adjuvant or palliative intent.Results: Seventy-one patients with PDGFRA exon 18 mutation were identified of whom 48 patients (69%) had a D842V mutation. Twenty-two (45.8%) D842V-mutated GIST patients received imatinib treatment, 16 had measurable disease. Fourteen out of the 23 (60.9%) patients with non-D842V mutations received imatinib treatment, eight had measurable disease. Two out of 16 (12.5%) D842V-mutated GIST patients had partial response, 3 patients (18.8%) had stable disease and 9 patients (56.3%) had progressive disease as best response. Two patients did not have follow-up computed tomography scans to assess response. Six out of 8 (75%) patients with non-D842V exon 18 mutations had partial response and two (25%) had stable disease as best response.Conclusion: Patients with D842V-mutated GISTs can occasionally respond to imatinib. In the absence of better therapeutic options, imatinib should therefore not be universally withheld in patients with this mutation. (C) 2017 Elsevier Ltd. All rights reserved.

Highlights • SBRT for liver metastases is a safe alternative for surgical resection or ablation. • High dose (>100 Gy) SBRT provides better local control than low dose (≤100 Gy) SBRT. • Toxicity rates of SBRT are low and do not increase after dose escalation. • Dose escalation is positively associated with overall survival., Introduction Stereotactic Body Radiation Therapy (SBRT) is a treatment option for patients with liver metastases. This study evaluated the impact of high versus low dose image-guided SBRT of hepatic metastases. Methods and materials This is a single-center retrospective study of patients with liver metastases treated with SBRT. For analyses, patients were divided into two groups: ≤100 Gy and >100 Gy near-minimum Biological Effective Doses (BED98%). The main outcomes were local control (LC), toxicity and overall survival (OS). Cox regression analyses were performed to determine prognostic variables on LC and OS. Results Ninety patients with 97 liver metastases (77% colorectal) were included. Median follow-up was 28.6 months. The two-year LC rates in the ≤100 Gy and >100 Gy BED98% group were 60% (CI: 41–80%) and 90% (CI: 80–100%), respectively (p = 0.004). Grade 3 toxicity occurred in 7% vs 2% in the ≤100 Gy and >100 Gy group (p = 0.23). Two-year OS rates in the ≤100 Gy and >100 Gy group were 48% (CI: 32–65%) and 85% (CI: 73–97%), respectively (p = 0.007). In multivariable Cox regression analyses, group dose and tumor volume were significantly correlated with LC (HR: 3.61; p = 0.017 and HR: 1.01; p = 0.005) and OS (HR: 2.38; p = 0.005 and HR: 1.01; p =

Background Schwannomas are rare tumours that pose a significant management challenge in the abdomen, retroperitoneum and pelvis. No data are available to inform management strategy. Methods A collaborative international cohort study, across specialist sarcoma units, was conducted to include adults presenting between 2000 and 2017 with histopathologically confirmed schwannomas within the abdomen, retroperitoneum or pelvis. Results Of 485 patients across 12 centres, 38 (7·8 per cent) were discharged without follow-up, 199 (41·0 per cent) underwent early resection and 248 (51·1 per cent) had radiological monitoring. Of these 248 patients, 96 (38·7 per cent) eventually had surgery, giving an overall resection rate of 60·8 per cent (295 of 485). At baseline, median tumour volume was 90·1 (i.q.r. 26·5–262·0) cm3. The estimated growth rate was 10·5 (95 per cent c.i. 9·4 to 11·6) per cent per year, and was consistent in the short term (within 2 years of diagnosis) and long term (beyond 2 years) (ρ = 0·405, P = 0·021). A decision to operate was more common in symptomatic patients (P < 0·001) and for rapidly growing tumours (growth rate more than 20 per cent per year) (P = 0·025). R0/R1 resection was achieved in 91·6 per cent of patients (263 of 287). Kaplan–Meier long-term recurrence rates after R0/R1 resection were 2·3 and 6·7 per cent at 3 and 5 years respectively. Conclusion Specific recommendations include: indications for early surgery, prediction of growth from radiological monitoring, promotion of selective submacroscopic resection and cessation of postoperative imaging surveillance.

10021 Background: Continuous combination of MAPK inhibition (MAPKi) and anti-PD-(L)1 has been investigated by several trials to improve outcome of BRAFV600 mutated melanoma patients. A major obstacle for continuous combination is the high frequency (~60%) of grade 3-4 treatment-related adverse events (TRAE) for which many patients need to discontinue (~40%). In a preclinical model we showed that short‐time MAPKi induces T cell infiltration and is synergistic with anti-PD‐1. In patients T cell infiltration increased after short-term MAPKi, while after > 2 weeks this was often diminished. The aim of this phase 2b study was to identify the optimal duration of MAPKi with dabrafenib (BRAFi) + trametinib (MEKi) in combination with pembrolizumab (anti-PD-1) in terms of safety, feasibility and immune-activating capacity. Methods: Treatment-naïve BRAFV600E/K mutant advanced melanoma patients started pembrolizumab (PEM) 200mg Q3W and were randomized in week 6 to continue PEM only (cohort 1) or to receive in addition intermittent dabrafenib (D) 150 mg BID + trametinib (T) 2mg QD for 2 x 1 week (cohort 2), 2 x 2 weeks (cohort 3), or continuous for 6 weeks (cohort 4). All cohorts continued PEM for up to 2 years. Primary endpoints were safety and treatment-adherence. Secondary endpoints were objective response rate (ORR, RECIST 1.1) at week 6, 12, 18 compared to baseline and PFS. Results: Between June 2016 and August 2018, 32 patients have been included; 56% were male, 50% had M1c disease and the majority had a BRAFV600E mutation (81%) and a baseline LDH level > ULN (87%). Grade 3-4 TRAE were observed in 12%, 12%, 50%, and 62% of patients in cohort 1, 2, 3, and 4, respectively. All planned D+T was given in 88%, 63%, and 38% of patients in cohort 2, 3, and 4. Most patients needed to interrupt or discontinue D+T due to fever or elevated liver enzymes. ORR at week 6, week 12, and week 18 were 38%, 62%, and 62% in cohort 1, 25%, 62%, and 75% in cohort 2, 25%, 50%, and 75% in cohort 3 and 0%, 62%, and 50% in cohort 4. After a median follow-up of 17.4 months, the median PFS of patients treated with PEM monotherapy was 10.6 months compared to 27.0 months for patients treated with PEM and short-term/intermittent D+T (p = 0.13). Conclusions: Combination of PEM plus intermittent D+T seems more feasible and tolerable than continuous triple therapy. Intermittent short-time combination therapy might be equally effective, enables therapy with MAPKi as a second line, and therefore warrants further investigation in a larger patient cohort. Clinical trial information: NCT02625337.

11011Background: PDGFRA D842V-mutated GISTs are known for their insensitivity to imatinib. However, in clinical practice responses have been observed in some patients. We describe the natural histo...