title: Secular trends in the incidence of cholangiocarcinoma in the USA and the impact of misclassification.
abstract: OBJECTIVE
  It has been reported that the incidence of intrahepatic cholangiocarcinoma (ICC) has increased in the USA, while extrahepatic cholangiocarcinoma (ECC) has decreased or remained stable. However, neither the recent trends nor the effects of the misclassification of Klatskin tumors are known.
  
  
  METHODS
  Using the Surveillance, Epidemiology, and End Results program databases, we calculated the average annual age-adjusted incidence rates (AA-IRs) of ICC and ECC in 4-year time periods (1992-1995, 1996-1999, 2000-2003, 2004-2007). These AA-IRs were calculated with misclassified as well as correctly classified Klatskin tumors. AA-IRs were also calculated based on age, sex, and race. Multivariable Poisson regression models were used to evaluate the secular trends of ICC and ECC.
  
  
  RESULTS
  The AA-IR of ICC was 0.92 in 1992-1995 and 0.93 in 2004-2007, while the AA-IR of ECC increased from 0.70 in 1992-1995 to 0.95 in 2004-2007. There was no significant trend in AA-IR of ICC (p = 0.07), while there was a significant increase in ECC across the 4-year time periods (p < 0.001). Klatskin tumors comprised 6.7% of CCs with approximately 90 and 45% misclassified as ICC during 1992-2000 and 2001-2007, respectively. Adjusted Poisson models showed no significant differences in the temporal trend of ICC or ECC due to misclassification of Klatskin tumors.
  
  
  CONCLUSIONS
  The incidence of ICC has remained stable between 1992 and 2007 with only slight fluctuations, while the incidence of ECC has been increasing. Misclassification of Klatskin tumors does not appear to play a significant role in the trends of CCs.
authors.affiliation: Houston VA Health Services Research and Development Center of Excellence, Michael E. DeBakey Veterans Affairs Medical Center, Houston, TX, USA, giatyson@hotmail.com.
authors.forename: Gia L
authors.initials: GL
authors.lastname: Tyson
authors.forename: Jawad A
authors.initials: JA
authors.lastname: Ilyas
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Duan
authors.forename: Linda K
authors.initials: LK
authors.lastname: Green
authors.forename: Mamoun
authors.initials: M
authors.lastname: Younes
authors.forename: Hashem B
authors.initials: HB
authors.lastname: El-Serag
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Davila
mesh_terms: D000368:Aged; D001650:Bile Duct Neoplasms / Q000145:classification / Q000453:epidemiology*; D001653:Bile Ducts, Intrahepatic / Q000473:pathology*; D018281:Cholangiocarcinoma / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D018285:Klatskin Tumor / Q000145:classification / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D044469:Racial Groups; D012042:Registries; D013997:Time Factors; D014481:United States / Q000453:epidemiology