Trends in female breast cancer among adolescent and young adults in Southeast Asia.

1597 Background: Breast cancer is the leading cancer among women globally and poses a growing public health challenge, particularly in adolescents and young adults (AYAs), defined as individuals aged 15–39 years. In Southeast Asia (SEA), rising breast cancer rates among AYAs are compounded by unique biological, socioeconomic, and healthcare barriers, including late-stage diagnosis and limited access to screening and treatment. However, regional data on incidence and mortality trends remain scarce. This study aims to analyze temporal trends in AYA breast cancer incidence and mortality across 11 SEA countries from 1990 to 2021 using data from the Global Burden of Disease (GBD) database. Methods: We extracted breast cancer incidence and mortality data for AYAs in SEA from the GBD database (1990–2021) for Brunei, Cambodia, Indonesia, Lao PDR, Malaysia, Myanmar, the Philippines, Singapore, Thailand, Timor-Leste, and Vietnam. Age-standardized rates (ASRs) were calculated, and temporal trends were evaluated using Estimated Annual Percent Change (EAPC) based on log-linear regression. Results: Breast cancer incidence among AYAs increased significantly across SEA from 1990 to 2021. Thailand reported the highest ASR in 2021 (11.78 per 100,000) and the most pronounced rise in incidence (EAPC 4.06). Significant increases were also observed in Vietnam (EAPC 2.92), Cambodia (2.63), and Laos (2.57). Mortality trends were heterogeneous: Singapore achieved a significant decline (EAPC -2.00), attributed to advancements in early detection and treatment, while Thailand, Indonesia, Vietnam, and Cambodia experienced rising mortality rates. In 2021, the highest mortality rates were recorded in Myanmar (2.54 per 100,000), Thailand (2.36 per 100,000), and the Philippines (2.17 per 100,000). Conclusions: The growing burden of AYA breast cancer in SEA reflects a combination of epidemiologic transitions, socio-economic shifts, and regional healthcare disparities. Rising incidence is linked to changes in reproductive behavior, lifestyle factors, and urbanization, while increased mortality highlights gaps in healthcare access and screening infrastructure. Urgent public health interventions tailored to AYA populations are needed to enhance early detection, improve treatment accessibility, and address disparities across SEA. Regional collaboration and investments in healthcare systems are critical to mitigating the growing burden of breast cancer among AYAs in this dynamic region.