AIM: Signal transducers and activators of transcription(STATs) are a family of transcription factors activated inresponse to cytokines and growth factors.Constitutiveactivation of Star3 has been observed in a growing numberof tumor-derived cell lines,as well as tumor specimensfrom human cancers.The purpose of this study was toinvestigate the expression of p-Stat3,activated form ofStat3,and its downstream mediators including cyclin D1and Bcl-X_L in colorectal carcinoma (CRC),and to explorethe possible mechanism of Stat3 signaling pathway in thetumorigenesis of colorectal carcinoma.METHODS: Tissue samples from 45 patients of primarycolorectal carcinoma were selected for studying Stat3signaling pathway protein expression.Western blot analysiswas used to measure the expression of p-Stat3,cyclin D1,and Bcl-x_L proteins in colorectal carcinomas.Furthermore,the expression patterns of these proteins were analyzed fortheir distribution at the cellular level by immunohistochemicalstaining of the tissues.RESULTS: Protein levels of p-Stat3,cyclin D1,and Bcl-X_Lwere increased in colorectal carcinomas compared withadjacent normal mucosae (P<0.05).Elevated levels of p-Star3 were correlated with the nodal metastasis and thestage (P<0.05).Overexpression of cyclin D1 was associatedwith the nodal metastasis (P<0.05).There was also asignificant correlation between the expressions of p-Stat3and cyclin D1 (r=-0.382,P<0.05).CONCLUSION: Constitutive activation of Stat3 may playan important role in the tumorigenesis of colorectalcarcinoma,and the detailed mechanism of Stat3 signalingpathway in CRC deserves further investigation. AIM: Signal transducers and activators of transcription (STATs) are a family of transcription factors activated in response to cytokines and growth factors. Status of the Star3 has been observed in a growing number of tumor-derived cell lines, as well as tumor specimens from human cancers. purpose of this study was to investigate the expression of p-Stat3, and activated form of Stat3, and its downstream mediators including cyclin D1 and Bcl-X_L in colorectal carcinoma (CRC), and to explore the possible mechanism of Stat3 signaling pathway in the tumorigenesis of colorectal carcinoma. METHODS : Tissue samples from 45 patients of primary colorectal carcinoma were selected for studying Stat3 signaling pathway protein expression. Western blot analysis was used to measure the expression of p-Stat3, cyclin D1, and Bcl-x_L proteins in colorectal carcinomas. Future Plus, the expression patterns of these proteins were analyzed fortheir distribution at the cellular level by immunohistochemical stain of the tissues.RESULTS: Protein levels of p-Stat3, cyclin D1, and Bcl-X_Lwere increased in colorectal carcinomas withadjacent normal mucosae (P <0.05). Elevated levels of p-Star3 were correlated with the nodal metastasis and thestage ). Overexpression of cyclin D1 was associated with the nodal metastasis (P <0.05). There was also asignificant correlation between the expressions of p-Stat3 and cyclin D1 (r = -0.382, P <0.05) .CONCLUSION: Constitutive activation of Stat3 may playan important role in the tumorigenesis of colorectalcarcinoma, and the detailed mechanism of Stat3 signalingpathway in CRC deserves further investigation.