Cancer incidence trends among young adults in Portugal, 2001–2022: A population-based study

INTRODUCTION: Cancer incidence is rising among young adults in several high-income countries, yet comprehensive data from Southern Europe, particularly Portugal, remain limited. We characterized temporal trends in cancer incidence among young adults (20-49 years) in Portugal between 2001 and 2022, comparing them with older adults (≥50 years). METHODS: This nationwide population-based cohort study included 1,102,774 incident cancer cases recorded by the Portuguese National Cancer Registry. Age-standardized incidence rates (ASIR) per 100,000 inhabitants were calculated using the European Standard Population. Temporal trends were analysed using joinpoint regression, estimating annual percentage changes (APC) and average annual percentage changes (AAPC) by sex, age group, and cancer type. RESULTS: Cancer cases increased from 36,604 in 2001 to 60,926 in 2022. Young adults accounted for 13.0% of all cases. Among young women, ASIR increased by 31.6% (from 156.2 to 205.6; AAPC: +1.48%), driven largely by breast cancer (+50.0%), thyroid (+94.1%), melanoma (+84.1%), and lung cancer (+78.7%). In contrast, young men showed stable overall ASIR (AAPC: -0.05%), with a biphasic pattern of increase (2001-2010) followed by decline (2010-2022). However, young men experienced substantial rises in colorectal (+56.6%), thyroid (+185.1%), and melanoma (+70.1%) incidence, alongside declines in stomach (-67.0%), oesophageal (-56.8%), and lung (-45.8%) cancers. Older adults demonstrated significant ASIR increases driven by trends before 2011, with subsequent stabilization or decline. CONCLUSIONS: Cancer incidence among young Portuguese adults is increasing, particularly among women, with sex-specific and site-specific patterns. While declines in tobacco-related cancers reflect successful prevention efforts, rising rates of breast, colorectal, thyroid, and melanoma in young adults signal the need for enhanced targeted prevention strategies and continued etiological research.