Abstract
BACKGROUND: Breast cancer (BC) poses an increasing threat to women's health, yet its characteristics in women of childbearing age (WCBA) are infrequently reported. This study aims to investigate the patterns and trends in BC incidence among WCBA over the past decades. MATERIALS AND METHODS: This study focuses on BC incidence in women aged 15-49 years, consistent with the WHO definition of WCBA. Estimates and 95% uncertainty intervals (UIs) for BC incidence in WCBA were obtained from the Global Burden of Diseases Study 2021. We utilized an age-period-cohort (APC) model to estimate the overall annual percentage change in incidence (net drift, % per year) and the annual percentage change within each age group (local drift, % per year). This model also provided fitted longitudinal age-specific rates adjusted for period deviations (age effects) and period/cohort relative risks (period/cohort effects) from 1992 to 2021. RESULTS: In 2021, the global incidence of BC among WCBA was 561.44 thousand (95% UI 519.76 to 606.99). Between 1992 and 2021, the estimated annual change in BC incidence among WCBA was 0.47 (95% CI 0.41-0.52) worldwide, ranging from -0.43 (95% CI -0.54--0.31) in High sociodemographic index (SDI) region to 2.03 (95% CI 1.97-2.1) in Low-middle SDI region. Local drift analysis showed that higher SDI regions had higher age-standardized incidence rates among WCBA, with age effects demonstrating similar patterns across different SDI regions and increasing risk with age. Notably, the rising trend in BC incidence among WCBA occurs at progressively younger ages. Globally, unfavorable period and cohort effects were observed. All SDI regions exhibited increased period and cohort risks, except for the High SDI region, which saw a reduction in incidence rates influenced by period and cohort effects, particularly among those born after 1996. CONCLUSION: The increasing incidence of BC among WCBA highlights the urgent need for effective intervention and preventive policies to alleviate this growing global burden.