Background: The extent to which improvements over time in breast cancer survival are related to earlier detection by mammography or to more effective treatments is not known.

Methods: At a comprehensive cancer care center, the authors conducted a retrospective cohort study of women ages 50 to 69 years who were diagnosed with invasive breast cancer (stages I through III) and were followed over 3 periods (1990-1994, 1995-1999, and 2000-2007). Data were abstracted from patient charts and included detection method, diagnosis, treatment, and follow-up for vital status in the institutional breast cancer registry (n = 2998). The method of detection was categorized as patient or physician detected or mammography detected. Cox proportional hazards models were used to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for 5-year disease-specific survival in relation to detection method and treatment factors, and differences in survival were analyzed using the Kaplan-Meier method.

Results: Fifty-eight percent of breast cancers were mammography detected, and 42% were patient or physician detected; 56% of tumors were stage I, 31% were stage II, and 13% were stage III. The average length of follow-up was 10.71 years. The combined 5-year disease-specific survival rate was 89% from 1990 to 1994, 94% from 1995 to 1999, and 96% from 2000 to 2007 (P < .001). In an adjusted model, mammography detection (HR, 0.43; 95% CI, 0.27-0.70), hormone therapy (HR, 0.47; 95% CI, 0.30-0.75), and taxane-containing chemotherapy (HR, 0.61; 95% CI, 0.37-0.99) were significantly associated with a decreased risk of disease-specific mortality.

Conclusions: Better breast cancer survival over time was related to mammography detection, hormone therapy, and taxane-containing chemotherapy. Treatment improvements alone are not sufficient to explain the observed survival improvements over time.