International variations in epidemiology of cancers of the extrahepatic biliary tract.

Previous studies of the descriptive epidemiology of biliary tract cancers have not differentiated among different types of biliary tract cancer because until recently the International Classification of Diseases (ICD) did not classify them separately. Recent versions of the ICD now distinguish cancers of the gallbladder, extrahepatic bile ducts, and ampulla of Vater. In order to describe more precisely the distribution of these three cancers, we obtained data from nine cancer registries throughout the world which used the eighth or ninth revision of the ICD. Sex-specific, age-adjusted disease rates were calculated for each disease. Log-linear models were used to evaluate the association of age and sex with the risk of acquiring each disease and to assess whether the risk of acquiring disease or the age and sex distribution of the three diseases varied by geographic location. Gallbladder cancer was the most common of the three diseases and occurred more frequently in females. Extrahepatic bile duct cancer was the next most common disease and occurred equally in both sexes. Cancer of the ampulla of Vater was the least common and was more common in males. The incidence of each of the diseases increased with age. The age and sex distributions of the different diseases different among the nine registries. Thus these three neoplasms differ in their descriptive epidemiology and should therefore be considered separately in clinical practice and in future investigations.