Power and limits of modern cancer diagnostics: cancer of unknown primary

Background: 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. Patients and methods: 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. Results: 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. Conclusion: These data suggest that improvements in the resolution and availability of powerful imaging techniques result in increasingly sensitive detection of tumors.