Cancer of Unknown Primary: Time Trends in Incidence, United States
METHODS: The Surveillance Epidemiology and End Results (SEER) registry was used to examine incidence rates, adjusted to the World Segi 1960 population, by demographic and tumor characteristics among patients diagnosed with CUP between 1973 to 2010. Annual percent changes in incidence rates were estimated using Joinpoint regression.
RESULTS:
The incidence rate of CUP was 5.3 per 100,000 and is consistent with reports from other countries. In the US, CUP incidence rates have been decreasing since the early 1980’s; 3.6 percent per year in the last two decades. US males and African Americans had the highest rates of CUP. The rates of non-microscopically confirmed CUP has dropped 2.6 percent per year since 1973, but 25% of CUP patients do not receive microscopic confirmation. Over 20% of patients were classified with a nonspecific histological type. Fifteen percent of patients receive radiation and in 83.2 percent of patients, surgery was not recommended. The incidence of CUP was higher in areas where smoking prevalence was greater; a ratio of 1.14:1.
CONCLUSIONS:
The US experienced earlier decreases in CUP incidence rates than other countries. Although the incidence of CUP is decreasing, we found racial disparities that may be due to insufficient diagnostic inquiry. Questions raised by the findings in this data provide hypotheses for further epidemiological and biological studies in the elucidation of CUP incidence and treatment.