Comparison of active and cancer registry-based follow-up for breast cancerin a prospective cohort study

The authors compared the relative effectiveness of two distinct follow-up d esigns in prospective cohort studies-the active approach, based on direct c ontact with study subjects, and the passive approach, based on record linka ges with population-based cancer registries-utilizing available information from the New York University Women's Health Study (WHS) and the New York S tate Cancer Registry (NYSCR), The analyses were limited to breast cancer ca ses identified during the period 1985-1992, for which follow-up was conside red reasonably complete by both the WHS and the NYSCR, Among 12,947 cohort members who reported a New York State address, 303 pathologically confirmed cases were identified through active follow-up and 284 through record link age. Sixty-three percent of cancers were identified by both sources, 21% by the WHS only, and 16% by the NYSCR only. The agreement was appreciably bet ter for invasive cancers. The percentage of cases identified only by the NY SCR was increased among subjects whose active follow-up was incomplete, as well as among nonwhites, obese patients, and parous patients. This suggests that relying on either type of follow-up alone may introduce certain biase s in evaluating risk factors for breast cancer. Combining both approaches a ppears to be a better strategy in prospective cohort studies.