title: Rapid reduction in the incidence of cancer of unknown primary. A population-based study.
abstract: BACKGROUND
  Cancer of unknown primary (CUP) carries a dismal prognosis due to the two hallmarks of 1) being metastatic with 2) no known specific treatment. An organ-labeled diagnosis of cancer should therefore be sought. In this study, we have analyzed population-based incidence and survival data of CUP over the latest 40 years.
  
  
  METHODS
  Complete national data on 23 004 CUP-patients from the Cancer Registry of Norway sampled from 1971 to 2010 are presented, with absolute and age-adjusted incidence rates correlated to the total cancer incidence. One-year relative survival rates were calculated.
  
  
  RESULTS
  The incidence of CUP increased both in absolute numbers and as a fraction of total cancer incidence during the first half of the period. There has been a substantial decrease in incidence over the latest 20 years, now being responsible of only 1.7% and 1.2% of the total cancer incidence in females and males, respectively, with an age-adjusted incidence rate of 3.5 and 3.8, respectively. The one-year relative survival rate has increased and was slightly below 20% for both sexes in 2010.
  
  
  CONCLUSIONS
  Better diagnostics, both radiological and pathological, is probably responsible for a substantially lower incidence. Improved treatment for cancers in general also benefits the CUP-group.
authors.affiliation: Department of Oncology, Oslo University Hospital, The Norwegian Radium Hospital , Oslo , Norway.
authors.forename: Odd Terje
authors.initials: OT
authors.lastname: Brustugun
authors.forename: Åslaug
authors.initials: Å
authors.lastname: Helland
mesh_terms: D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D009382:Neoplasms, Unknown Primary / Q000453:epidemiology* / Q000401:mortality / Q000517:prevention & control*; D009664:Norway / Q000453:epidemiology; D011379:Prognosis; D012042:Registries; D015996:Survival Rate; D013997:Time Factors