CDA and neoplasm: In general, cytidine (that is, the substrate of CDA) was found in mouse serum (that is, ~1 μM; Extended Data Fig. 5k) and in the tumor interstitial fluid (TIF; that is, ~10 μM; Fig. 5f; as previously reported32) and also in vitro in absolute fetal bovine serum (FBS) and in the culture medium of both macrophages and dying KPC FC1245 cells (Extended Data Fig. 5k).