Eur J Cancer

Introduction: There is growing concern about rising cancer incidence among adults younger than 50 years. This collaborative study within the Spanish Network of Cancer Registries (REDECAN) aimed to examine cancer incidence trends in young adults in Spain.

Material and methods: This population-based observational study used data from 15 cancer registries. All newly diagnosed cancer cases in individuals aged 20-49 years between 1993 and 2018 were included. For each sex and cancer site, truncated age-standardized incidence rates per 100,000 person-years were calculated using the European standard population (TASR-E). Temporal trends were assessed using Joinpoint regression analysis to estimate the annual percent change (APC).

Results: A total of 153,599 new cancer cases (58% in women) were diagnosed during the study period. Trends were heterogeneous, with more increases observed in women. Incidence rose for kidney (APC=2.5%), thyroid (4.0%), and Hodgkin lymphoma (1.1%) in men and for pancreas (2.0%), Hodgkin (2.1%) and non-Hodgkin (1.7%) lymphoma in women. Several digestive system (stomach, colon, rectum), breast and cervical cancers increased significantly among the youngest adults (<40 years old). In contrast, incidence declined for larynx, lung, urinary bladder, and liver cancers in both sexes (APCs ranging between -3.1% to -8.7%), and for lip, oral cavity, and pharynx cancers in men.

Discussion: In young adults, incidence of smoking-associated cancers has decreased substantially, whereas some obesity-associated cancers have increased among adults 20-39 years old. These findings underscore the need for stronger cancer prevention measures and a better understanding of the rising incidence of some cancers in young adults.