AIM:To investigate cell cycle proteins in chronic hepatitis C virus infection in order to analyze their role in the process of hepatocyte transformation and to characterize their prognostic properties. METHODS:Subjects of the current study included 50 cases of chronic hepatitis C(CHC) without cirrhosis,30 cases of CHC with liver cirrhosis(LC) ,and 30 cases of hepatitis C-related hepatocellular carcinoma(HCC) admitted to the Department of Hepato-Gastroenterology,Theodor Bilharz Research Institute(TBRI) ,Giza,Egypt.Fifteen wedge liver biopsies,taken during laparoscopic cholecystectomy,were also included as normal controls.Laboratory investigations including urine and stool analysis,liver function tests and prothrombin concentration;serologic markers for viral hepatitis and ultrasonography were done for all cases of the study together with immunohistochemical analysis using primary antibodies against Cyclin D1,Cyclin E,p21,p27 and Rb/p105 proteins. RESULTS:Normal wedge liver biopsies didn’t express Cyclin E or Rb/p105 immunostaining but show positive staining for Cyclin D1,p21 and p27.Cyclin D1 expressed nuclear staining that was sequentially increased from CHC to LC(P<0.01) to HCC(P<0.001) cases;meanwhile,Cyclin E revealed nuclear positivity only in the case of HCCs patients that was directly correlated to Rb/p105 immuno-reactivity.The expression of p21 and p27 was significantly increased in CHC and LC cases compared to normal controls and HCCs with no significant difference between well-and poorlydifferentiated tumors.p21 showed only a nuclear pattern of staining,while,p27 presented with either cytoplasmic and/or nuclear reactivity in all studied cases.Correlation analysis revealed a direct relation between Cyclin D1 and p21 in CHC cases(P<0.001) ,between Cyclin D1 and Cyclin E in HCCs(P<0.01);however,an inverserelationship was detected between Cyclin D1 and p21 or p27(P<0.001) and between p21 and Rb/p105(P<0.05) in HCCs. CONCLUSION:Upregulation of Cyclin D1 in CHC plays a vital role in the development and differentiation of HCC;while,Cyclin E may be a useful marker for monitoring tumor behavior.p21 and p27 can be used as predictive markers for HCC.Furthermore,higher expression of Rb/p105 as well as inverse relation with p21 and histologic grades suggests its important role in hepatic carcinogenesis. A investigator of To investigate cell cycle proteins in chronic hepatitis C virus infection in order to analyze their role in the process of hepatocyte transformation and to characterize their prognostic properties. METHODS: Subjects of the current study included 50 cases of chronic hepatitis C (CHC) without cirrhosis, 30 cases of CHC with liver cirrhosis (LC), and 30 cases of hepatitis C-related hepatocellular carcinoma (HCC) admitted to the Department of Hepato-Gastroenterology, Theodor Bilharz Research Institute (TBRI), Giza, Egypt. Fifteen wedge liver biopsies, taken during laparoscopic cholecystectomy, were also included as normal controls. Laboratory tests including urine and stool analysis, liver function tests and prothrombin concentration; serologic markers for viral hepatitis and ultrasonography were done for all cases of the study together with immunohistochemical analysis using primary antibodies against Cyclin D1, Cyclin E, p21, p27 and Rb / p105 proteins. RESULTS: Normal wedge liver biopsies didn Cysclin D1 was expressed in nuclear staining that resulted in the was increased from CHC to LC (P <0.01) to HCC (P <0.001) cases; whilewhile the expression of cyclin E or Rb / , Cyclin E revealed nuclear positivity only in the case of HCCs patients that was directly correlated to Rb / p105 immuno-reactivity. The expression of p21 and p27 was significantly increased in CHC and LC cases compared to normal controls and HCCs with no significant difference between well and poorly differentiated tumors. p21 showed only a nuclear pattern of staining, while, p27 presented with either cytoplasmic and / or nuclear reactivity in all studied cases. Correlation analysis revealed a direct relation between Cyclin D1 and p21 in CHC cases (P <0.001 ), between Cyclin D1 and Cyclin E in HCCs (P <0.01); however, an inverse relationship was detected between Cyclin D1 and p21 or p27 (P <0.001) and between p21 and Rb / p105 : Upregulation of Cyclin D1 in CHC plays a vital role in the development and differentiation of HCC; while, Cyclin E may be a useful marker for monitoring tumor behavior. p21 and p27 can be used as predictive markers for HCC.Furthermore, higher expression of Rb / p105 as well as as inverse relation with p21 and histologic grades suggests its important role in hepatic carcinogenesis.