?Background
Early-onset cancers, generally defined as those diagnosed in individuals aged 15–49 years, represent a growing global challenge and contribute substantially to premature mortality. Previous studies indicate that females experience a disproportionately higher incidence of overall early-onset cancers than males. However, critical gaps remain in understanding whether sex disparities in total early-onset cancer incidence have changed over time across countries. In addition, the global spatiotemporal evolution of early-onset cancers among females, both overall and by cancer type, remains poorly characterised. The United Nations’ Sustainable Development Goals (SDGs), particularly SDG 3·4 (reducing premature mortality by one-third) and SDG 5 (achieving gender equality), call for urgent, evidence-based action to address these cancer inequalities.
Objectives
We aimed to examine (1) the most recent global incidence patterns of all early-onset cancers and eight selected early-onset cancer types among females, (2) temporal trends in the female-to-male age-standardised incidence rate (ASIR) ratio for all early-onset cancers combined, and (3) spatiotemporal trends in the incidence of early-onset cancers among females across countries.
Methods
Using GLOBOCAN 2022, we identified the seven most incident cancers among females (cancers of the colorectum, lung, breast, cervix uteri, corpus uteri, ovary, and thyroid), as well as gallbladder cancer with female dominance. We described the global distribution and female-to-male ASIR ratios in 2022 for all cancers and the eight selected cancers. Female incidence trends and female-to-male ASIR ratios for these cancers and for all cancers combined from 1998 to 2017 were analysed using Cancer Incidence in Five Continents Plus (CI5 Plus) data from 38 countries. Country-specific changes in ASIRs were estimated using Joinpoint regression, and Bayesian spatiotemporal models were applied, accounting for temporal and country effects.
Results
In 2022, an estimated 2,010,793 new cases of early-onset cancer occurred in females and 1,087,755 in males, yielding a female-to-male ASIR ratio of 1·85 for all cancers combined. Between 1998 and 2017, the female-to-male ASIR ratio increased from 1·55 to 1·74, and female ASIRs for all early-onset cancers rose significantly in 24 of 38 countries (AAPC range 0·41–4·54%), with the largest increases observed in east Asia, particularly China, the Republic of Korea, and Japan. Asia and Europe emerged as major incidence hotspots, with rapid increases observed in Cyprus, Japan, Ireland, and Spain. For individual cancer types, a surge in thyroid and breast cancer incidence was evident across most regions. Hotspot countries shifted from Europe to Asia for early-onset lung and ovarian cancers among females. Spatial convergence was evident for corpus uteri, cervical, and breast cancers, indicating progressive homogenisation of global incidence and narrowing regional disparities.
Conclusions/Implications
The growing disproportionate burden of early-onset cancers among females represents a pressing public health priority and a major challenge to achieving health equity. Shifting spatiotemporal patterns reveal emerging hotspots and highlight the need to investigate biological, social, and environmental drivers of sex disparities. These findings support more targeted cancer control strategies by identifying priority geographic regions, developmental contexts, and population groups, thereby informing resource allocation and policy planning to accelerate progress towards Sustainable Development Goals 3·4 and 5.
 

Spatiotemporal classification of all cancers and eight selected cancers