Long-term incidence and survival trends in cancer of the gallbladder and extrahepatic bile ducts in Denmark, Finland, Norway and Sweden with etiological implications related to Thorotrast

Cancers of the gallbladder and extrahepatic bile ducts (called here "GBC" because gallbladder cancer is the main component) are rare in Europe, including the Nordic countries. Their incidence has varied for unknown reasons and we hypothesize that Thorotrast, a previously used carcinogenic radiographic contrast medium, has contributed to the incidence trends. We obtained incidence and survival data from the NORDCAN database, which includes cancer registry data from Denmark (DK), Finland (FI), Norway (NO) and Sweden (SE), which are globally the oldest national cancer databases, starting from 1943 in DK, 1953 in FI and NO and 1960 in SE, and extending to 2016. The incidence trend for GBC showed a broad maximum around 1980 in men (close to 3/100 000) and women (4/100 000), except for NO, where this phenomenon was not seen. In 1955, FI and NO incidence rates were equal but FI rates peaked and later declined similar to DK and SE rates. By 2010, the incidence was similar in all Nordic countries, for both men and women, at close to 2.0/100 000. Birth cohort analysis showed strong effects for countries other than NO. Relative 1-year survival increased for men from 20% to about 50% and similarly for women although at a 5 percentage points lower level. Survival in NO was better than in other countries in the 1980s. Thorotrast, causing a high risk of GBC, was extensively used in the Nordic countries between 1930 and end of 1940s, with the exception of NO, where these was no documented use. These data suggest that Thorotrast influenced GBC epidemiology and probably worsened survival in certain periods.