Tehran University of Medical Sciences International Journal of Hematology-Oncology and Stem Cell Research 2008-2207 14 3 2020 07 02 181 187 Mozaffar Aznab Department of Internal Medicine, Taleghani Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran Seyed Majid Ahmadi School of Medicine, , Yasuj University of Medical Sciences, Yasuj, Iran Sedigheh Khazaei Molecular Pathology Research Center, Imam Reza University Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran Seyed Mojtaba Ahmadi Department of Clinical Psychology, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran Mansour Khazaei Taleghani University Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran Hamid Hamdi Armi Hospital, Sanandaj, Kurdistan 2019 05 15 2020 02 12 Background: Thymidylate synthase is one of the target enzymes of 5-fluorouracil. However, the clinical and prognostic significance of TS expression in gastric cancer has remained controversial. In this study, the expression of thymidylate synthase was evaluated in gastric cancer patients treated with combinational chemotherapy; moreover, the association between TS expression and clinicopathologic characteristics and overall survival of the patients were also assessed. Materials and Methods: In this descriptive study, 89 pathological samples were gathered from patients at Kermanshah hospitals during 2008-2017. The survival status of patients was recorded and their overall survival was evaluated individually. Results: The average survival period for low and high thymidylate synthase groups was 54 and 50 months, respectively, meaning higher survival time in the lower thymidylate group. But this difference was not statistically significant (log Rank=0.88). In addition, sex, stage, recurrence, and survival had no significant difference between the low and high expression of thymidylate synthase groups (p=0.89). Conclusion: The results clearly indicated that the level of thymidylate synthase is not a significant modulator of 5- fluorouracil in gastric cancer patients. Nevertheless, evaluation of the level of the enzymes and markers, as well as their effects, is highly recommended for accurate selection of chemotherapeutical strategies. https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/view/1133 https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/download/1133/833