Systematic underreporting of the population-based incidence of pancreatic and biliary tract cancers
Background. Incidence rates of cancers of the pancreas and biliary tract, typically derived from cancer registers, have been reported to be decreasing. This study tested whether pancreatic and biliary tract cancers are underreported in the Swedish Cancer Register (CR). Methods. The concordance of pancreatic and biliary tract cancer diagnoses in 1990–2009 between CR and the Swedish Patient Register (PR) were evaluated through record linkage. To further assess the completeness of these cancer diagnoses in both CR and PR, record linkage was also made to the Swedish Causes of Death Register (DR). Results. A total of 31 067 cases of pancreatic cancer and 14 273 cases of biliary tract cancer were identified in CR or PR. Altogether, 44% of the pancreatic cancers and 44% of the biliary tract cancers were registered in PR only, and not in CR. The concordance between CR and PR declined from 63% in the years 1990–1994 to 44% in 2005–2009 for pancreatic cancer. The corresponding figures for biliary tract cancer were 60% and 37%. This decline in concordance was also observed with increasing age, e.g. the concordance between CR and PR for pancreatic cancer declined from 62% in patients < 60 years to 36% among patients ≥ 80 years. The corresponding figures for biliary tract cancer were 52% and 38%. Conclusion. There is an overwhelming underreporting of pancreatic and biliary tract cancers within the Swedish Cancer Register, which has increased during recent years. The reported decreasing incidence rates for pancreatic and biliary tract cancers might therefore be incorrect.