Background and purpose: It is reported that Hes1 is related to the progression and metastasis of many kinds of tumor. This study was to investigate the expression of Hes1 in colon cancer and its effect on tumourformation ability of SW620 cells. Methods: The expression of Hes1 in colon cancer tissues and control normal samples was analyzed by immunohistochemistry and quantitative reverse transcription-polymerase chain reaction (qRTPCR)

and the relationship between Hes1 expression and differentiation in human colon cancer was detected. Hes1 overexpressing SW620 cell lines were established

and the expression of Hes1 mRNA and protein was detected by qRTPCR and Western blot simultaneously. We also detected the effect of Hes1 on the ability of tumour-formation in Hes1 overexpressing SW620 cells in nude mice in vivo. Results: We found that Hes1 was expressed in almost all normal tissues

particularly at the bottom of the crypts

and in all cancer tissues

including moderate and poorly differentiated cancer samples and well-differentiated cancer samples. In addition

the expression of Hes1 in poorly differentiated cancer samples was higher than that observed in well-differentiated tumor (P0.05). After stably transfected Hes1 in SW620 colon cancer cell lines

Hes1 was overexpressed successfully (P0.05). We injected 1×105 Hes1-overexpressing colon cancer cells and the control cells into nude mice subcutaneously

and found Hes1-overexpressing tumours exhibited significantly bigger size compared with that observed in controls. The growth of the Hes1-overexpressing tumours was found to be slightly faster than those of the controls. Conclusion: Hes1 is overexpressed in colon cancer than that in normal tissue

and Hes1 is upregulated in poorly differentiated cancer samples compared with welldifferentiated tumour samples. Hes1 has a positive influence on the ability of tumour-formation in SW620 cells in vivo.