Cancer patients without a known primary: Incidence and survival trends in Sweden 1960-2007

Background. Metastatic cancer from an unknown primary tumour ( CUP) is a common and heterogeneous clinical entity. In Sweden like in many other countries, the continuum of care for such patients remains to be established. Material and methods. Data on CUP cases reported to the Swedish Cancer Registry during 1960 through 2007 was used to assess time trends for incidence, survival, and histological tumour type. Results. There was an upward trend for the age-adjusted incidence until the late 1990s. This roughly paralleled the increase for all reported cancers during the same period. The increase of CUP mainly concerned patients aged above 50 years, and tumours classified as adenocarcinomas. The relative survival at 12 months after a diagnosis of CUP was estimated at 20%. However, after 12 months the relative survival levelled of and the 5-year estimate was 10-15% which suggests that a small proportion of CUP cases may be cured. Relative survival was highly dependent on age with substantially better outcome for young patients, particularly those aged below 30 years. We observed no time trend for survival. Discussion. Cases diagnosed as CUP includes patients with metastatic spread from a wide variety of tumours although certain tumour types probably are overrepresented, for example, cancers in sites that are difficult to examine clinically. Incidence trends probably represent the sum of trends for these cancers as well as diagnostic trends. The decreased incidence observed during the last decade might thus be explained in terms of a combination of improved diagnostic methods to detect primary tumours and decreasing incidence for e. g. pancreatic cancer and lung cancer among males. There is a need of evidence-based programs that define the continuum of care for CUP patients. Such a program is currently being developed through collaboration between all health care regions in Sweden.