Do increases in mortality from intrahepatic cholangiocarcinoma reflect a genuine increase in risk? Insights from cancer registry data in Scotland.

The mortality from intrahepatic cholangiocarcinoma has increased recently in England and Wales and elsewhere. This study aims to examine recent trends in the incidence of intrahepatic cholangiocarcinoma in Scotland, to assess the extent to which changes in diagnostic practice may be influencing the observed trends, and to consider whether the results are compatible with a genuine increase in the risk of this cancer. Cancer registration (intrahepatic cholangiocarcinoma and anatomically adjacent cancers) data from Scotland 1968-1997 were analysed, including examination of trends in the percentage of cases recorded as being microscopically-verified. Since the late 1960s, the incidence of intrahepatic cholangiocarcinoma has increased approximately eight-fold in both sexes in Scotland. However, the proportion of cases verified microscopically has decreased substantially since the late 1970s, presumably due to an increasing reliance on radiological imaging for diagnosis. Despite this change in diagnostic practice, the incidence of microscopically-verified intrahepatic cholangiocarcinoma has also increased. While changes in diagnostic practice and misclassification could explain, at least part of, the observed increase in incidence of intrahepatic cholangiocarcinoma, a genuine increase in the risk of this cancer in the Scottish population seems probable. Further work is indicated to examine international trends in incidence, and to assess whether incidence differs within countries according to characteristics such as area of residence, socio-economic status, ethnic origin or occupation.