Abstract
BACKGROUND: Breast cancer (BC) has been increasing globally, though it is unclear whether the increases are seen across all age groups and regions and whether changes in rates can be primarily attributed to decreasing fertility rates. We investigated age-specific trends in BC incidence and mortality from 1990 to 2017, worldwide and by region, and evaluated whether incidence trends are explained by decreases in fertility. METHODS: We used country-level data to examine trends in BC incidence and mortality rates from 1990 to 2017 by region and age group. Linear mixed models were used to estimate age-specific rates from baseline models of year and were compared to fertility-adjusted models for incidence. RESULTS: The global BC mortality rate increased overall by 0.23% per year (95% CI=0.20, 0.25), with statistically significant increases in the under 50 and 70 and over age groups, and in 5 out of 7 regions. The global BC incidence rate increased overall by 1.44% per year (95% CI=1.42, 1.47), with statistically significant increases in all age groups, and in 6 out of 7 regions. After adjusting for fertility, the incidence annual percent change (APC) remained statistically significant (APC=0.84, 95% CI=0.81, 0.88), in all age groups, and in 6 of 7 regions. INTERPRETATION: The global increase in BC mortality is seen in most age groups and regions. The global increase in BC incidence is seen in all age groups and is highest in women under 50; increases remained in most regions even after considering declining fertility rates. FUNDING: Breast Cancer Research Foundation and National Cancer Institute.