Despite there being only a small number of NR2F1-positive primary tumor cells, we observed that ~50% of CTCs were NR2F1-positive (Fig. 4b, “CTCs” bar), suggesting that tumor cells are programmed for dormancy either before they intravasate (since acquisition can occur in hypoxic microenvironments21) or during intravasation. This evidence concerns the gene NR2F1 and neoplasm.