Abstract: Genetic Polymorphisms in CLOCK and Increased Risk of Breast Cancer: A Case Control StudyXiaoling ZHU, Hongji DAI, Mingli CAO, Hong ZHENG, Yanrui ZHAO, Fengju SONG, Kexin CHENCorrespondence to: Kexin CHEN, E-mail: chenkexin1963@yahoo.comDepartment of Epidemiology, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, ChinaThis work was supported by the National Natural Science Foundation of Chia (No. 30771844)Abstract Objective: To investigate the relationship between single nucleotide polymorphisms in the CLOCK gene andsusceptibility to breast cancer in a Chinese population. Methods: Genotyping was performed using Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) in 1,499 histologically confirmed breast cancer cases and 1,592 healthycontrols. SPSS16.0 was used for data processing. Results: There were significant differences in genotype distribution of CLOCKpolymorphisms between the breast cancer cases and controls ( χ2= 9.712, P = 0.008 ). Multivariate logistic regression analysis showedthat the carriers of the CT genotype had an increased risk of breast cancer ( adjusted OR = 1.41, 95% CI = 1.07-1.87 ), an individualwho carried the T variant ( CT/TT ) had a 35% increased risk of breast cancer ( adjusted OR = 1.35, 95% CI = 1.04-1.76 ). Stratifiedanalysis indicated that the negative effect of T variant ( CT/TT ) was more evident in postmenopausal subjects who had no history ofbenign disease or cancer. Conclusions: CLOCK ( rs3805151, C > T ) polymorphisms were associated with an increased risk of breastcancer. Further studies on people of different ethnicities and functional studies are expected to confirm these findings.Keywords Breast cancer; CLOCK gene; Single nucleotide polymorphism; Genetic susceptibility; Risk factors