Tobacco contributes to the toll of chronic hepatitis B in China, to the tune of 50,000 liver cancer deaths every year, according to a study published in the October 20th issue of the International Journal of Cancer.

"Liver cancer and liver cirrhosis are common causes of death in China, where chronic lifelong hepatitis B infection is a major cause of both diseases," Dr. Zhang-ming Chen, of the University of Oxford, UK, and colleagues write. To examine whether smoking is a cofactor for the development of liver cancer, they retrospectively studied the smoking habits of 36,000 adults who died from liver cancer (cases) and 17,000 who died from cirrhosis (controls). Among men, the standardized risk ratio for mortality from liver cancer for smokers versus nonsmoker was 1.36. In the general male population, this correlated to absolute risks of death from liver cancer before age 70 years of about 3% for nonsmokers and 4% for smokers. "In most parts of China, however, liver cancer is largely restricted to the 10% to 12% of adults who are chronically infected with the hepatitis B virus, among whom the risks of death from liver cancer before age 70 must therefore be about 25% for nonsmokers and 33% for smokers," Dr. Chen and colleague calculate. Women who smoked also had a significant excess of liver cancer deaths, according to the investigators. However, they note that fewer women than men smoke (17% versus 62%, respectively). "These associations indicate that tobacco is currently responsible for about 50,000 liver cancer deaths each year in China, chiefly among men with chronic HBV infection," the investigators conclude.

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