What cancers are increasing in young adults: a population-based study of incidence trends in adults 20–49 years old in the South of Spain

BACKGROUND: Recent studies have documented sharp increases in the incidence of several types of cancer in young adults, highlighting the need to monitor and understand epidemiological trends in this population. The aim of this study was to analyze cancer incidence trends among young adults (20-49 years) in the province of Granada, Spain, from 1985 to 2019 and to compare the trends in young adults to those observed in adults over 50 years old. METHODS: We analyzed all incident cancer cases (ICD-10 codes C00-C96), diagnosed between 1985 and 2019, in individuals aged ≥ 20 years old, from the population-based Cancer Registry of Granada, Spain. Age-adjusted incidence rates (truncated age-standardized rates) were calculated and analyzed using Joinpoint Regression to estimate annual percentage changes (APC), stratified by age group (20-49 vs. older 50+), sex, and cancer site. RESULTS: 18,601 cases were identified in young adults, 58.0% in women. Overall cancer incidence increased to a larger extent in young women (APC of + 2.4%, 95% CI [2.1, 2.8]) than in young men (+ 0.8%, [0.5, 1.1]). In young men, cancer sites with significant increasing trends included thyroid (+ 9.6%, [3.9, 15.5]), testicle (+ 7.6% [6.0, 9.3]), skin melanoma (+ 4.5% [2.8, 6.1]), non-melanoma skin cancer (NMSC) (+ 3% [2.3, 3.8]), and brain and central nervous system (CNS) tumors (+ 2% [0.9, 3.2]). In young women, cancer sites with significant increases included CNS (+ 5.6% [3.1, 8.1]), NMSC (+ 4.3% [3.5, 5.1]), thyroid (+ 3.5% [2.3, 4.7]), skin melanoma (+ 3.2 [1.8, 4.5]), breast (+ 1.8% [1.4, 2.3]), and corpus uteri (+ 3.1% [1.2, 4.9]). Cancer sites where incidence increased to a larger extent among young vs. older persons included: rectum, thyroid, and testicular cancer for men and NMSC, rectum, CNS, lung, non-Hodgkin lymphoma, bladder, and corpus uteri for women. CONCLUSION: The incidence of several types of cancer has increased significantly among young adults in southern Spain, with more pronounced increases among women. There is an urgent need to investigate the underlying causes of increasing early-onset cancer trends and explore changes in early detection strategies.