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Extramedullary (EM) disease in patients with acute myeloid leukemia (AML) is a known phenomenon. Since the prevalence of EM AML has so far only been clinically determined on examination, we performed a prospective study in patients with AML. The aim of the study was to determine the prevalence of metabolically active EM AML using total body 18Fluorodesoxy-glucose positron emission tomography/computed tomography (18FDG-PET/CT) imaging at diagnosis prior to initiation of therapy. In order to define the dynamics of EM AML throughout treatment, PET-positive patients underwent a second 18FDG-PET/CT imaging series during follow up by the time of remission assessment. A total of 93 patients with AML underwent 18FDG-PET/CT scans at diagnosis. The prevalence of PET-positive EM AML was 19% with a total of 65 EM AML manifestations and a median number of two EM manifestations per patient (range, 1-12), with a median maximum standardized uptake value of 6.1 (range, 2-51.4). When adding those three patients with histologically confirmed EM AML who were 18FDG-PET/CT negative in the 18FDG-PET/CT at diagnosis, the combined prevalence for EM AML was 22%, resulting in 77% sensitivity and 97% specificity. Importantly, 60% (6 of 10) patients with histologically confirmed EM AML still had active EM disease in their follow up 18FDG-PET/CT. 18FDG-PET/CT reveals a high prevalence of metabolically active EM disease in AML patients. Metabolic activity in EM AML may persist even beyond the time point of hematologic remission, a finding that merits further prospective investigation to explore its prognostic relevance. (Trial registered at clinicaltrials.gov identifier: 01278069.)

188 Background: (Stereotactic) Ablative radiotherapy (aRT) in patients with oligometastatic prostate cancer is safe, achieves high local control rates and its clinical benefit is currently being addressed in clinical trials. However, the selection of patients benefitting most from aRT remains unclear. Moreover, the highly specific and sensitive multimodality functional imaging modality, 68Ga-PSMA-PET-CT/-MR, is widely available. Therefore, we retrospectively evaluated the efficacy of PSMA-PET guided local aRT in low volume oligometastatic castration resistant prostate cancer (CRPC) patients. Methods: Fifteen patients with metachronous oligometastatic CRPC as diagnosed on PSMA-PET were treated with local aRT. Nine patients were treated with a conventionally fractionated regime (25 x 2 Gy) and six with stereotactic hypofractionated RT (3 x 10 Gy), while in all androgen deprivation was continued. The time to PSA-progression, i.e. PSA-nadir + 2 ng/ml (PSA+2) was estimated with the Kaplan-Meier method and compared to an individually estimated time to PSA+2 according to the individually calculated pre-RT PSA doubling time (PSA-DT). Results: At staging PSMA-PET, the median PSA was 3.4 ng/ml (range 1.3 -14.5) and the median PSA-DT was 3.2 months (range 0.6 - 15.3). In four patients no PSA-response after aRT was observed. The responding eleven patients (73%) had a mean decrease in PSA-level of 80% from baseline. The mean time to PSA-nadir was 10.7 months (range 4.5 - 11.5). The mean time to PSA+2 or last follow-up was 15.6 months [95%CI: 9.7 - 21.4] compared to 3.3 months [95%CI: 1.5 - 5.1] estimated PSA-DT without local aRT (p < 0.001). Conclusions: A relevant subset of patients with 68Ga PSMA-PET-detected oligometastatic low volume CRPC had a meaningful PSA-response with aRT. They were reverted into an earlier stage of their disease again. A prospective clinical trial on this clinically highly relevant question is being prepared.

Only approximately 30% of patients with colorectal cancer liver metastasis qualify for curative therapy, which is in most cases liver lesion resection. Due primarily to the extent of the tumors and patient comorbidities, palliative therapy remains the only option in non-resection cases. Palliation enables local, symptomatic control and prolonged survival in some cases. As established methods are continuously improved, new palliative therapy methods are tested in clinical trials and subsequently introduced into clinical practice. The present review provides an overview of current colorectal liver metastasis treatment when resection is not an option. This review gives the basis for an interdisciplinary decision making process for the treatment of liver metastasis.

Introduction: Acute myeloid leukemia (AML) may present with either concomitant or isolated extramedullary (EM) AML. Data on the prevalence of EM AML are based on retrospective and clinical analyses which rely on findings from physical examination only or on coincidental findings in standard imaging procedures and range from 2.5 to 9.1% (Bakst et al., Blood 2011;118(14):3785-3793). Previous studies identified EM AML as a prognostic factor in patients with AML. 18Fluorodesoxy-Glucose Positron Emission Tomography – Computed Tomography (18FDG/PET-CT) is able to detect highly metabolic tissue and has proven efficacy in imaging studies for various types of malignant diseases. In a pilot study in patients with histologically proven EM AML, we were able to demonstrate a sensitivity of 90% using 18FDG/PET-CT imaging and found additional EM sites in 60% of the patients (Stölzel et al., Haematologica 2011;96(10):1552-1556). The aim of this prospective, observational study was to determine the prevalence of EM AML in patients with newly diagnosed or relapsed AML using 18FDG/PET-CT (ClinicalTrials.gov Identifier: NCT01278069). Patients and Methods: A total of 94 patients with AML (newly diagnosed AML, n = 85 and relapsed AML, n = 9) underwent total body 18FDG/PET-CT scans at diagnosis after giving informed consent. Patients with EM diagnosed by 18FDG/PET-CT underwent a second 18FDG/PET-CT scan after induction chemotherapy. The median age of all patients was 61 years (range, 27 to 79 years). Patients were included only if a delay of ≤ 5 days of initiation of induction- or re-induction chemotherapy was clinically justifiable to perform the study. 18FDG/PET-CT scans were performed using a Siemens Sensation 16 as part of a biograph (Siemens, Knoxville, TN, USA) with i.v. application of 18FDG (range of activity 223 to 433 MBq) and 120 ml i.v. contrast media Ultravist 370 (Bayer Schering Pharma, Leverkusen, Germany). Adverse reactions due to the application of i.v. 18FDG and i.v. contrast media did not occur. Results: Total body 18FDG/PET-CT imaging detected highly metabolic manifestations suggestive for EM AML in 21 patients (22%). During follow-up after induction chemotherapy, 18FDG-avid EM was still observed in 50% of all PET-positive patients. In comparison with PET-negative patients, those with PET-positive EM AML had a higher bone marrow blast count, a higher prevalence of FAB M5 morphology, higher peripheral WBC, higher serum LDH, and less frequent FLT3-ITD mutations. Sites of EM AML were connective tissue (n=4), parenchymal tissues (n=8), and lymph nodes (n=15). In patients with clinically overt EM AML (n=8) additional EM manifestations were detected in 62% (n=5). In 13 patients, samples from EM sites were obtained for histology review – in 10 patients histology confirmed the occurrence of EM AML in these sites, indicating a specificity of 77%. Importantly, in the remaining patients in whom histology could not confirm EM AML, concomitant malignant tumors were found. Extrapolating these results on the entire cohort, the prevalence of EM AML in newly diagnosed and relapsed AML is 17%. Conclusions: Our study is the first to prospectively evaluate 18FDG/PET-CT imaging for the diagnosis of EM AML. According to our results, 18FDG/PET-CT is a useful and safe tool in order to detect EM AML with a high specificity. We found a prevalence of EM AML of 17%. This is two- to eightfold higher, than in previously reported clinical studies. Integration of 18FDG/PET-CT-based imaging procedures as adjunct for response assessment in these patients seems to be important. Further development of other PET-based imaging procedures and integration in the setting of relapse after allogeneic hematopoietic stem cell transplantation might be necessary and will contribute to a better understanding of the biology and prognostic role of EM AML and the development of targeted treatment strategies in patients with AML. Disclosures No relevant conflicts of interest to declare.