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The orogenic peridotite body Mohelno represents an ultramafic igneous rock of asthenospheric origin located in the Moldanubian Zone (the eastern margin of the Bohemian Massif, Czech Republic), which is interpreted as a deep part of the thickened orogenic root developed during Variscan continental convergence. The Mohelno body represents a large scale fold structure that underwent a complex tectonic and metamorphic history. It records deformation in mantle, emplacement into lower orogenic crust and exhumation within granulite complex to middle crustal levels. The oldest part of the evolution is partially recorded by the crystallographic preferred orientation of olivine and orthopyroxene preserved in coarse-grained relics of the Mohelno peridotite. This original structure is reworked by pervasive deformation resulting in ultramylonitic fabric. Later in the middle crustal conditions, the peridotite is affected by the serpentinization to various degree, thus original anisotropy of magnetic susceptibility (AMS) record is disturbed and difficult to interpret. Modeling of AMS using the topotactic relationships between olivine and orthopyroxene and newly growing serpentine minerals + magnetite helped us to understand the AMS evolution during the serpentinization process. This enables us to relate distinct AMS fabrics to original mantle structure of olivine and pyroxenes and to late deformation evolution of already serpentinized peridotite., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

1 Czech Geological Survey, Klarov 3, 118 21 Prague 1, Czech Republic; pavel.hanzl@geology.cz 2 Ecole et Observatoire des Sciences de la Terre, Universite de Strasbourg, UMR 7516 of CNRS, 1 rue Blessig, 67084 Strasbourg Cedex, France 3 Institute of Petrology and Structural Geology, Charles University in Prague, Faculty of Science, Albertov 6, 128 43 Prague 2, Czech Republic 4 Institute of Paleontology and Geology, Mongolian Academy of Sciences, Ulaanbaatar 15160, Mongolia 5 School of Geology and Mining Engineering, MUST, P.O. Box 654, Ulaanbaatar, Mongolia 6 State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China * Corresponding author

BACKGROUND & AIMS: Patients with Lynch syndrome are at high risk for developing colorectal cancer (CRC). Regular colonoscopic surveillance is recommended, but there is no international consensus on the appropriate interval. We investigated whether shorter intervals are associated with lower CRC incidence and detection at earlier stages by comparing the surveillance policies in Germany, which evaluates patients by colonoscopy annually, in the Netherlands (patients evaluated at 1-2-year intervals), and Finland (patients evaluated at 2-3-year intervals). METHODS: We collected data from 16,327 colonoscopic examinations (conducted from 1984 through 2015) of 2747 patients with Lynch syndrome (pathogenic variants in the MLH1, MSH2, or MSH6 genes) from the German HNPCC Consortium, the Dutch Lynch Syndrome Registry, and the Finnish Lynch Syndrome Registry. Our analysis included 23,309 person-years of cumulative observation time. Time from the index colonoscopy to incident CRC or adenoma was analyzed using the Kaplan-Meier method; groups were compared using the log-rank test. We performed multivariable Cox regression analyses to identify factors associated with CRC risk (diagnosis of CRC before the index colonoscopy, sex, mutation, age, and presence of adenoma at the index colonoscopy). RESULTS: The 10-year cumulative CRC incidence ranged from 4.1% to 18.4% in patients with low-and high-risk profiles, respectively, and varied with age, sex, mutation, and prior detection of CRC or adenoma. Observed colonoscopy intervals were largely in accordance with the country-specific recommendations. We found no significant differences in cumulative CRC incidence or CRC stage at detection among countries. There was no significant association between CRC stage and[GRAPHICS]time since last colonoscopy. CONCLUSIONS: We did not find a significant reduction in CRC incidence or stage of detection in Germany (annual colonoscopic surveillance) than in countries with longer surveillance intervals (the Netherlands, with 1-2-year intervals, and Finland, with 2-3-year intervals). Overall, we did not find a significant association of the interval with CRC risk, although age, sex, mutation, and prior neoplasia were used to individually modify colonoscopy intervals. Studies are needed to develop and validate risk-adapted surveillance strategies and to identify patients who benefit from shorter surveillance intervals.

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