Tumour cells were collected in FACS buffer, centrifuged for 8 minutes at 500g, and 100,000 cells were resuspended in 100 μL of lysis buffer (Tris HCl 10mM, NaCl 10mM, MgCl2 3mM, Igepal 0,1%) and centrifuged (500 g) for 25 min at 4°C. Supernatant was discarded and nuclei were resuspended in 50 μL of reaction buffer (Tn5 transposase 2,5 μL, TD buffer 22,5 μL and 25 μL H2O - Nextera DNA sample preparation kit, Illumina). The transposase reaction was performed for 30 min at 37°C and then blocked by addition of 5μL of clean up buffer (NaCl 900mM, EDTA 300mM). . DNA was purified using the MinElute purification kit (QIAGEN). DNA libraries were PCR amplified (Nextera DNA Sample Preparation Kit, Illumina), and size selected for 200 to 800 bp (BluePippin, Sage Sciences) following manufacturers' protocols