XRCC5 and neoplasm: We detected CK + SYP + cells in serial-passaged PDX tumor tissue (up to at least 6 passages, passage 2 shown-Fig. 2c) that co-stained with the human Ku80 protein (Supplementary Fig. 1b), indicating that these dual positive cells in human PDA are tumor cell-derived, since normal islets would not be expected to survive the time it takes for PDXs to establish nor propagate in serial passage.