Methods of cancer case selection: implications for research

The race, age, and sex differences between clinically and microscopically diagnosed cancer cases for a total of 63,301 incident cases for 18 sites are reported. The cases, diagnosed during 1973-1978, were drawn from the Cancer Surveillance Section in the Division of Epidemiology at the Michigan Cancer Foundation in Detroit, a participant in the Surveillance, Epidemiology, and End Results (SEER) program. Although microscopically diagnosed cases and those diagnosed by other methods differed by race and sex for a few sites, the two case groups differed by age for 15 of the 18 sites examined. Cases without microscopic diagnoses (i.e., clinical diagnoses) tended to be older than microscopically confirmed cases. These findings indicate that in studies of certain cancer sites, the method of case selection could affect results pertaining to age differences in exposure to and effects of relevant risk factors.