Tezacitabine is a cytidine derivative patented by Merrell Dow Pharmaceuticals, Inc. as an antineoplastic and antiviral agent. Tezacitabine acts as irreversible ribonucleotide reductase inhibitor and DNA chain terminator. Tezacitabine shows as potent activity in a broad spectrum of tumor cell lines and in vivo tumor models, including human colon, prostate, and breast tumor xenografts, In clinical trials combination of Tezacitabine and 5-Fluorouracil exerts favor influences in patients with advanced solid tumors particularly in patients with esophageal and other gastrointestinal carcinomas.