Increase in Distant Stage Breast Cancer Incidence Rates in US Women Aged 25-49 Years, 2000-2011: The Stage Migration Hypothesis

Background. Unexplained increases have been reported in incidence rates for breast cancer diagnosed at distant stage in younger U.S. women, using data from the Surveillance, Epidemiology and End Results (SEER) Program. Methods. This report focused on recent SEER trends (2000-2011) in age-standardized incidence rates of invasive breast cancer at ages 25-39 and 40-49 years and the hypothesis that stage migration may have resulted from advances in detecting distant metastases at diagnosis. Results. Increases in the rates for distant stage were roughly equal to decreases in the rates for the most advanced stage subgroups within regional stage; this was evident for estrogen receptor (ER) negative cancers, associated with poorer prognosis, but not for ER positive cancers. The 3-year relative survival rate increased over time for distant stage (especially in the ER positive subgroup) and regional stage but not for localized stage; these trends do not contradict the stage-migration hypothesis. Conclusions. Findings provide some support for stage migration as one explanation for the recent increase in incidence of distant stage breast cancer, but additional studies are needed using other databases.