Thiarabine (also known as OSI-7836) is a new-generation deoxycytidine nucleoside analog with potent anticancer activity. As with other nucleoside analogs, Thiarabine is a prodrug and requires intracellular phosphorylation by deoxycytidine kinase to the active form (Thiarabine-triphosphate), which then competes with deoxycytidine for incorporation into DNA resulting in cell death. In xenograft studies using lung, colon, pancreatic, breast, and melanoma models, Thiarabine shows superior antitumor activity in most of these tumors, particularly in lung and pancreatic models, compared with gemcitabine, cisplatin, and paclitaxel. Thiarabine seems to be less schedule dependent than gemcitabine, showing antitumor activity with a variety of schedules in preclinical studies. In clinical trials, Thiarabine administration was associated with excessive fatigue, and despite changes in its schedule and duration of administration.