OBJECTIVE: To estimate prevalence of childhood-onset Duchenne and Becker muscular dystrophies (DBMD) in 6 sites in the United States by race/ethnicity and phenotype (Duchenne muscular dystrophy [DMD] or Becker muscular dystrophy [BMD]). METHODS: In 2002, the Centers for Disease Control and Prevention established the Muscular Dystrophy Surveillance, Tracking, and Research Network (MD STARnet) to conduct longitudinal, population-based surveillance and research of DBMD in the United States. Six sites conducted active, multiple-source case finding and record abstraction to identify MD STARnet cases born January 1982 to December 2011. We used cross-sectional analyses to estimate prevalence of DBMD per 10 000 boys, ages 5 to 9 years, for 4 quinquennia (1991–1995, 1996–2000, 2001–2005, and 2006–2010) and prevalence per 10 000 male individuals, ages 5 to 24 years, in 2010. Prevalence was also estimated by race/ethnicity and phenotype. RESULTS: Overall, 649 cases resided in an MD STARnet site during ≥1 quinquennia. Prevalence estimates per 10 000 boys, ages 5 to 9 years, were 1.93, 2.05, 2.04, and 1.51, respectively, for 1991–1995, 1996–2000, 2001–2005, and 2006–2010. Prevalence tended to be higher for Hispanic individuals than non-Hispanic white or black individuals, and higher for DMD than BMD. In 2010, prevalence of DBMD was 1.38 per 10 000 male individuals, ages 5 to 24 years. CONCLUSIONS: We present population-based prevalence estimates for DBMD in 6 US sites. Prevalence differed by race/ethnicity, suggesting potential cultural and socioeconomic influences in the diagnosis of DBMD. Prevalence also was higher for DMD than BMD. Continued longitudinal surveillance will permit us to examine racial/ethnic and socioeconomic differences in treatment and outcomes for MD STARnet cases.

Background: Although recent findings suggest that de novo stage IV breast cancer is increasing in premenopausal women in the United States, contemporary incidence and survival data are lacking for stage I–III cancer. Methods: Women aged 20–29 (n = 3826), 30–39 (n = 34 585), and 40–49 (n = 126 552) years who were diagnosed with stage I–III breast cancer from 2000 to 2015 were identified from the Surveillance, Epidemiology, and End Results 18 registries database. Age-adjusted, average annual percentage changes in incidence and 5- and 10-year Kaplan-Meier survival curves were estimated by race and ethnicity, stage, and hormone receptor (HR) status and grade (low to well and moderately differentiated; high to poorly and undifferentiated) for each age decade. Results: The average annual percentage change in incidence was positive for each age decade and was highest among women aged 20–29 years. Increased incidence was driven largely by HR+ cancer, particularly HR+ low-grade cancer in women aged 20–29 and 40–49 years. By 2015, incidence of HR+ low- and high-grade cancer each independently exceeded incidence of HR− cancer in each age decade. Survival for HR+ low- and high-grade cancer decreased with decreasing age; survival for HR− cancer was similar across age decades. Among all women aged 20–29 years, 10-year survival for HR+ high-grade cancer was lower than that for HR+ low-grade or HR− cancer. Among women aged 20–29 years with stage I cancer, 10-year survival was lowest for HR+ high-grade cancer. Conclusions: HR+ breast cancer is increasing in incidence among premenopausal women, and HR+ high-grade cancer was associated with reduced survival among women aged 20–29 years. Our findings can help guide further evaluation of preventive, diagnostic, and therapeutic strategies for breast cancer among premenopausal women.