title: Power and limits of modern cancer diagnostics: cancer of unknown primary.
abstract: Cancer of unknown primary (CUP) is diagnosed at a metastatic stage but no diagnostic effort is spared to find the primary cancers because these will guide the treatment. Consequently, the diagnostic work-up for CUP is more comprehensive than for any other cancer, resulting in detection of second cancers unrelated to CUP. We want to use the detection rate of second cancers as a measure of efficacy of the diagnostic modalities in finding tumors, assuming that the detection rates have increased with modern technologies.
  
  
  
  The number of CUP patients identified in the nation-wide Swedish Database was 28,574 and relative risks (RRs) for second cancers were recorded in three periods from 1980 through 2008. The first 5 months after CUP were considered critical for second cancers to be diagnosed during the intense work-up for CUP.
  
  
  
  Among second cancers, diagnosable by computed tomography or magnetic resonance imaging, there was a large 6.80-fold increase in RR immediately following CUP diagnosis from the period 1980-1989 to 2000-2008. Over the same periods, the increase in in situ tumors was 7.16-fold.
  
  
  
  These data suggest that improvements in the resolution and availability of powerful imaging techniques result in increasingly sensitive detection of tumors.
authors.affiliation: Division of Molecular Genetic Epidemiology, German Cancer Research Centre (DKFZ), Heidelberg, Germany; Center for Primary Health Care Research, Lund University, Malmö, Sweden. Electronic address: k.hemminki@dkfz.de.
authors.forename: K
authors.initials: K
authors.lastname: Hemminki
authors.affiliation: Division of Molecular Genetic Epidemiology, German Cancer Research Centre (DKFZ), Heidelberg, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Liu
authors.affiliation: Cancer Gene Therapy Group, Molecular Cancer Biology Program, Transplantation Laboratory, Haartman Institute, Finnish Institute for Molecular Medicine, University of Helsinki, Helsinki, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Heminki
authors.affiliation: Center for Primary Health Care Research, Lund University, Malmö, Sweden; Stanford Prevention Research Center, Stanford University School of Medicine, Palo Alto, USA.
authors.forename: J
authors.initials: J
authors.lastname: Sundquist
mesh_terms: D006801:Humans; D015994:Incidence; D009378:Neoplasms, Multiple Primary / Q000175:diagnosis* / Q000453:epidemiology*; D009382:Neoplasms, Unknown Primary / Q000175:diagnosis*; D012306:Risk