Background: The presence of mutated KRAS ( mut KRAS ctDNA) in plasma samples has been consistently shown to be a negative prognostic indicator in pancreatic cancer (PC). Only small pilot studies have evaluated the value of serial mut KRAS ctDNAmeasurements in PC. Patients and methods:The aim of the present study was to explore the potential of repeated mut KRAS ctDNA measurements for response prediction and therapy monitoring in advanced PC patients. We used the BEAMing technology to determine levels of mut KRAS ctDNA, CA 19-9, CEA and CYFRA 21-1 in 284 plasma samples of 54 patients with advanced PC receiving gemcitabinebased chemotherapy. Absolute levels and kinetics of mut KRAS ctDNA, CA 19-9, CEA and CYFRA 21-1 were correlated to radiological response, progression-free and overall survival.Results: mut KRAS ctDNA was present in a majority of advanced PC patients (n ¼ 36/54, 67%) and indicated tissue KRAS mutation status with a high sensitivity (75%) and specificity (100%). The presence of mut KRAS ctDNA, as well as higher levels of CA 19-9, CEA and CYFRA 21-1 before initiation of the first-line chemotherapy, was significantly correlated to an adverse overall survival. During therapy, changes in mut KRAS ctDNA levels were more rapid and pronounced than changes in protein-based tumor markers. A decrease in mut KRAS ctDNA levels during therapy was an early indicator of response to therapy, while there was no significant correlation between kinetics of CA 19-9, CEA or CYFRA 21-1 and response to chemotherapy during the first four weeks of treatment. Repeated mut KRAS ctDNA measurements during follow-up appeared to be superior to protein-based tumor markers in detecting progressive disease (sensitivity: 83%, specificity: 100%). Conclusion:mut KRAS ctDNA kinetics appear to be a powerful and highly specific tool in early response prediction and therapy monitoring of advanced PC patients receiving chemotherapy.

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2 cases of anaplastic thyroid cancer are described which developed after treatment of hyperthyroidism with iodine-131.

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