Mortality after breast cancer as a function of time since diagnosis by estrogen receptor status and age at diagnosis

Our aim was to estimate how long-term mortality following breast cancer diagnosis depends on age at diagnosis, especially if at a young age, tumor estrogen receptor (ER) status, and the time already survived. We used the population-based Australian Breast Cancer Family Study which followed-up 1,196 women enrolled during 1992-99 when aged <60 years at diagnosis with a first primary invasive breast cancer, over-sampled for younger ages at diagnosis, for whom tumor pathology features and ER status were measured. There were 375 deaths (median follow-up=15.7; range=0.8-21.4, years). We estimated the mortality hazard as a function of time since diagnosis using a flexible parametric survival analysis with ER status a time-dependent covariate. For women with ER-negative tumors compared with those with ER-positive tumors, 5-year mortality was initially higher (P<.001), similar if they survived to 5 years (P=0.4), and lower if they survived to 10 years (P=0.02). The estimated mortality hazard for ER-negative disease peaked at ~3 years post-diagnosis, thereafter declined with time, and at 7 years post-diagnosis became lower than that for ER-positive disease. This pattern was more pronounced for women diagnosed at younger ages. Mortality was also associated with lymph node count (hazard ratio (HR)=2.52 [95% CI:2.11-3.01] per 10 nodes) and tumor grade (HR=1.62 [95% CI:1.34-1.96] per grade). The risk of death following a breast cancer diagnosis differs substantially and qualitatively with diagnosis age, ER status and time survived. For women who survive >7 years, those with ER-negative disease will on average live longer, and more so if younger at diagnosis