82 Chapter 4 staging procedure. The age of selected controls was within the same age range as the cancer patients. Ethical approval Ethical approval was provided by the Medical Ethical Committee of the VU University Medical Center for the use of samples collected within the SOLUTION1 study (METc 2016.213) (Trial registration ID: NL56664.029.16), samples archived under the URIC biobank (TcB 2018.657) and samples archived under the biobank containing leftover material of the Dutch national cervical cancer screening program (TcB2020.245). Women participating in the screening program were informed that their residual cervical sample could be used for anonymized research and had the opportunity to opt out. Only left-over material from women who did not opt out was used. All women were 18 years or older and signed informed consent. For the FFPE tissue samples of normal endometrium, the Code of Conduct for Responsible Use of Left-over Material of the Dutch Federation of Biomedical Scientific Societies was adhered (27). Sample processing Urine of endometrial cancer patients and healthy female controls were collected from home in collection tubes containing 0.6 M ethylenediaminetetraacetic acid (EDTA; final concentration: 40 mM), to maintain DNA quality during transport, following a previously validated storage and collection protocol (28). In a previous feasibility study analyzing different urine fractions for optimal endometrial cancer detection using methylation markers, full void urine was shown to perform best and therefore used in the current study (25). The cervicovaginal self-samples were collected using a dry-brush device (Evalyn Brush, Rovers Medical Devices, Oss, The Netherlands). After collection of the urine and cervicovaginal self-sample, these samples were sent together within 72 hours by regular mail to the Pathology department of Amsterdam UMC, location VU University Medical Center, and processed directly upon arrival. Urine was stored at -20°C, and the dry brush was placed in 1.5 mL ThinPrep PreservCyt medium (Hologic, Marlborough, MA, US), vortexed and stored at 4°C. The clinician-taken cervical scrapes were obtained with a Cervex-Brush (Rovers Medical Devices, Oss, The Netherlands), immediately preserved in 10 mL Thinprep Preservcyt medium and stored at 4°C. FFPE tissue samples were cut into serial sections, and the first and last sections were Hematoxylin and Eosin (H&E) stained for a histopathological review by a pathologist (MB) to confirm the presence of endometrial cancer or normal endometrium.
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