Trends in breast cancer mortality by stage at diagnosis among young women in the United States.

BACKGROUND: Assessing trends in breast cancer survival among young women who are largely unaffected by breast cancer screening will provide important information regarding improvements in the effectiveness of cancer care for breast cancer in the last few decades. METHODS: The cohort for this study consisted of women who were diagnosed with breast cancer between ages 20 and 39 years from the Surveillance, Epidemiology, and End Results program's 9-registry areas from 1975 to 2015. Trends in the breast cancer incidence rate and survival were assessed among young women. RESULTS: Among women aged 20 to 39 years, breast cancer incidence increased from 24.6 per 100,000 in 1975 to 31.7 per 100,000 in 2015 (annual percent change, 0.5; 95% confidence interval [CI], 0.4-0.6). Among women with breast cancer, 5-year breast-cancer-specific survival increased significantly from 74.0% during 1975 to 1979 to 88.5% during 2010 to 2015 (hazard ratio for dying from breast cancer for 2010-2015 vs 1975-1979, 0.37; 95% CI, 0.32-0.41). The increase in cancer-specific survival reached a plateau in 2005; however, among young women with metastatic breast cancer, it continued to increase after 2005, from 45.6% during 2005 to 2009 to 56.5% during 2010 to 2015 (hazard ratio for dying from breast cancer for 2010-2015 vs 2005-2009, 0.74; 95% CI, 0.60-0.92). Similar patterns also were observed for 5-year overall survival and among women aged 20 to 29 years and those aged 30 to 39 years. CONCLUSIONS: There were substantial improvements in the effectiveness of breast cancer treatment on overall and cancer-specific survival from 1975 to 2015. However, improvements appeared to have reached a plateau after 2005, except among young women with metastatic breast cancer, in whom survival continued to improve throughout the period.