Objective To investigate the expression of sLc22A1 8,an impfinted tumor suppressor gene,in breast cancer and explore the relationship between expression of SLC22A18 and the pathogenesis of breast cancer. Methods Real-time quantitative reverse transcriptase-polymerase chain reaction was applied on 46 cases of infiltrating duetal breast carcinoma(IDC),46 csges of corresponding adjacent noncancerous tissues and 20 benign breast tissues in order to detect mRNA expression of SLC22A18 gene.Protein expression was detected by immunohistochemistry.Statistical analysis was carried out to analyse the correlation between SLC22A18 gene expression and various elinical parameters in these breast cancer patients. Results SLC22A18 mRNA expression in 46 IDC tissues Was lower than that in all corresponding adjacent non-cancerous tissues(Z=-4.900,P＜0.01).SLC22A18 mRNA expression was lower in breast cancer eases,when compared with that in benign cases(Z=-3.182,P＜0.01).SLIC22A18 mRNA expression in 40 IDCs Was lower than that in 6 dutal carcinoma in situ(part of IDC)(Z=-2.022,P＜0.05).There was a decreased or completely diminished SLC22A18 protein expression in breast cancer.A significant difference of SLC22A18 protein expression was also observed in IDC and benign groups(P＜0.05).Neither mRNA nor protein expression of SLC22A18 gene correlated with clinieopathologic parameters such as age of patients,size of tumor,ehnical stage,pathologic subtype,histologlc grade or lymph node metastasis(P＞0.05).Condusion Decreased expression of SLC22A18 gene may play an important role in the carcinogenesis of IDC.