title: An audit of cancer of unknown primary notifications: A cautionary tale for population health research using cancer registry data.
abstract: BACKGROUND
  Cancer of unknown primary (CUP) is a common cancer yet little is known about the reliability of incidence data.
  
  
  METHODS
  We audited 574 CUP (C80.9) diagnoses (median age 81 years) registered by the New South Wales (NSW) Central Cancer Registry (2004-2007) in a cohort of Australian Government Department of Veterans' Affairs clients. The registry did not clarify diagnoses with notifiers during this period due to interpretation of privacy legislation. For the audit, current registry practice was applied by seeking additional information from CUP notifiers and reclassifying diagnoses as necessary. In addition, clinicopathological characteristics were extracted from notifications. Fisher's exact test and Student's t-test were used to compare the demographic and clinicopathological characteristics of the CUP subgroups. Age/sex-standardised CUP incidence rates and 95% confidence intervals were calculated, standardised to the 2001 Australian population.
  
  
  RESULTS
  172 (30.0%) cases were reclassified to a known primary site, mostly cutaneous, and nine (1.6%) were found to be non-malignant diagnoses. After the audit the age/sex-standardised CUP incidence rates decreased from 26.0 (95% CI 21.2-30.8) to 15.9 (95% CI 12.5-19.3) per 100,000 person-years. Of the 393 remaining CUP cases, 202 (51%) were registered on the basis of a clinical diagnosis (46 by death certificate only) and 191 (49%) by pathological diagnosis (79 by cytology alone). Compared to cases with a pathological diagnosis, cases with a clinical diagnosis were older (85.6 vs. 82.0 years, p<0.001), and the reported number and location of metastases differed (p<0.001); metastatic sites were more likely to be unspecified for clinical diagnoses (36.1% vs. 4.2%).
  
  
  CONCLUSIONS
  Cancer registry processes can markedly influence CUP incidence. Future population-based CUP research should take this into account, and consider stratification by basis of diagnosis due to differences in patient and tumour characteristics.
authors.affiliation: Adult Cancer Program, Prince of Wales Clinical School, University of New South Wales, Australia. Electronic address: claire.vajdic@unsw.edu.au.
authors.forename: Claire M
authors.initials: CM
authors.lastname: Vajdic
authors.affiliation: Adult Cancer Program, Prince of Wales Clinical School, University of New South Wales, Australia.
authors.forename: Chuang Ching
authors.initials: CC
authors.lastname: Er
authors.affiliation: Faculty of Pharmacy, University of Sydney, Australia.
authors.forename: Andrea
authors.initials: A
authors.lastname: Schaffer
authors.affiliation: School of Public Health, University of Sydney, Australia.
authors.forename: Timothy
authors.initials: T
authors.lastname: Dobbins
authors.affiliation: Adult Cancer Program, Prince of Wales Clinical School, University of New South Wales, Australia.
authors.forename: Lucy
authors.initials: L
authors.lastname: Wyld
authors.affiliation: Adult Cancer Program, Prince of Wales Clinical School, University of New South Wales, Australia.
authors.forename: Nicola S
authors.initials: NS
authors.lastname: Meagher
authors.affiliation: CUP Action, Australia.
authors.forename: Jane
authors.initials: J
authors.lastname: Barrett
authors.affiliation: Adult Cancer Program, Prince of Wales Clinical School, University of New South Wales, Australia.
authors.forename: Robyn L
authors.initials: RL
authors.lastname: Ward
authors.affiliation: Faculty of Pharmacy, University of Sydney, Australia; School of Public Health, University of Sydney, Australia.
authors.forename: Sallie-Anne
authors.initials: SA
authors.lastname: Pearson
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D009382:Neoplasms, Unknown Primary / Q000145:classification* / Q000453:epidemiology*; D009517:New South Wales; D012042:Registries / Q000592:standards*
keywords: Audit; CUP; Cancer registry; Descriptive epidemiology; Incidence; Legislation