Objective To investigate the hallmark of primary Cyclins expressed in diiferent colorectal tissues,and illustrate the laws and significance of primary Cyclins expressed in progression of human colorectal carcinogenesis.Methods Primary Cyclins (D1,E,A,B1 ) and ki67 expressed in single cells detached from 30 cases of normal colon mucosa,26 cases of colorectal adenomas and 121 cases of colorectal adenocarcinomas were analyzed by using flow cytometry.The expression types of primary Cyclins were classified according to the roles and the patterns of primary Cyclins expressed in cell cycle.The results and clinicopathomorphological data were analyzed.Results The positive expression rate and the expression levels of primary Cyclins,especially Cyclins ( E,B1 ),were discrepant in different layers of normal colon mucosal tissues,which were attenuated gradually from crypt to luminal surface.The positive expression rate and the levels of Cyclins expressed were correlated with the activity of proliferation in colon mucosal tissue.The expression of Cyclins (D1,A) was only located in crypt cells.There were no Cyclins expressed in the differentiated cells,such as luminal surface cells.The expression patterns of primary Cyclins could be classified three types in colorectal adenomas:Type Ⅰ,low expression of Cyclins ( E,B1 ),and no expression of Cyclins ( D1,A) ; Type Ⅱ,high expression of Cyclins ( E,B1 ) by different patterns,and low expression of Cyclins (DI,A); Type Ⅲ,high expression of Cyclins (D1,E,A,B1 ).The expression patterns of Cyclins were different in colorectal adenomas with different size,pathological features,and proliferative activity.The expression patterns of primary Cyclins could be classified five types in colorectal adenocarcinomas:Type Ⅰ,high expression of Cyclins (D1,E,A,B1 ) ; Type Ⅱ,low expression of Cyclin D1,and high expression of Cyclins ( E,A,B1 ) by different patterns; Type Ⅲ,no expression of Cyclin D1,and high expression of Cyclins (E,A,B1 ) by different patterns; Type Ⅳ,no expression of Cyclin D1,and low expression of Cyclins (E,A,B1 ) by different patterns; Type Ⅴ,no expression of Cyclins.The expression types of primary Cyclins were strongly linked to invasive depth and lymph node metastasis of colorectal adenocarcinomas (P <0.01 ),the degree of invasion,and the degree and the rate of lymph node metastasis were increased gradually from type Ⅰ to type Ⅴ.The expression types of primary Cyclins were also significantly associated with disease stage (TNM stage).The proportion of stage Ⅳ disease was increased gradually from type Ⅰ to type Ⅴ.Conclusion The expression level of Cyclins is attenuated gradually in the progression of cell regeneration,which may be correlated with controlled proliferation and terminal differentiation of cells.The high expression level of primary Cyclins may be necessary for the continued growth of adenomas,the degree of intraepithelial neoplasia,and carcinogenesis. There were many types of primary Cyclins expressed in different colorectal adenocarcinomas.The expression types of primary Cyclins were correlated to clinicopathological features.The expression level of primary Cyclin was declined with tumor progression. Key words: Colorectal adenocarcinomas; Cell cycle; Cyclin; Proliferation cell nuclear antigen; Flow cytometry