Relative Survival With Early-Stage Breast Cancer in Screened and Unscreened Populations.

Relative survival and disease-specific survival are two statistics that measure net survival from a cancer diagnosis, excluding other causes of death. In most cases, these two rates are comparable. However, in some cancer types for which cancer screening is performed, relative survival is often greater than disease-specific survival. This divergence has been attributed to mechanisms such as the "healthy user effect" and overdiagnosis of indolent tumors detected by screening. Using relative survival rate as a marker of these mechanisms, we examined the association of breast cancer screening with relative survival rates for women diagnosed with early-stage breast cancer. In population-based data from the National Cancer Institute's Surveillance, Epidemiology and End Results registry, we examined relative survival rates in women diagnosed with stage I breast cancer or ductal carcinoma in situ who were in highly screened vs less-highly screened groups, based on time period, age group, and insurance status. In this analysis, relative survival rates for early-stage breast cancer were higher than disease-specific survival, even exceeding 100% in populations experiencing higher rates of screening (ie, women diagnosed during the era of widespread uptake of mammography, age older than 40 years, and women with health insurance coverage). The favorable outcomes observed in screen-detected breast cancers are at least in part attributable to the healthy user effect and overdiagnosis of indolent tumors. Therefore, survival rates may not accurately reflect the effectiveness of cancer screening. These findings have implications for counseling of patients and future clinical studies of active monitoring approaches in breast cancer.