In a retrospective cohort study of entecavir-treated patients, the cumulative incidence of hepatocellular carcinoma was found to be 3.7 percent after 5 years of follow-up, compared with nearly four times as high as 13.7 percent in untreated controls. Tetsuya Hosaka, MD, from Tokyo, reported at the 63rd annual meeting of the American Association for the Study of Liver Diseases (AASLD). Unlike the control group, which consisted almost exclusively of patients with cirrhosis, the cumulative 5-year incidence was 38.9%, and only 7% in the entecavir-treated group. There was no significant difference between the groups of patients without cirrhosis, with a cumulative incidence of 2.5% reported for entecavir treatment and 3.5% for the control group. The same type of drug, particularly lamivudine (3TC), has also been shown to reduce the incidence of liver cancer in patients with chronic hepatitis B, Hosaka said. But lamivudine resistance develops rapidly, making long-term treatment difficult. In contrast, entecavir developed resistance mutations in only 0.8 percent of patients, and none of those developed cancer. From 2004 to 2010, Hosaka and colleagues recruited consecutive patients treated with entecavir at Toranomon Hospital, as well as historical controls treated between 1973 and 1999 (before the approval of the nucleoside analogs) for comparison. There were 316 patients in each of the treatment and control groups. Hosaka and colleagues found that factors affecting 5-year cancer incidence included: entecavir treatment: hazard ratio (HR) 0.37, 95% CI 0.15 to 0.91 (P=0.03); age: HR 1.06 per year, 95% CI 1.03 to 1.09 (P< 0.001); pre-existing cirrhosis: HR 4.28, 95% CI 1.88 to 9.73 (P=0.013); HBV e antigen: HR 2.26, 95% CI 1.88-4.34 (P=0.014); platelet count below 1.5×105/mm3: HR 5.64, 95% CI 2.13-15 (P=0.001). This result is not surprising, but they do add to the growing body of clinical evidence - that treating hepatitis B prevents cancer.