Temporal Trends in Behavioural Risk Factors for Cancers with Rising Incidence in Younger Adults: An Analysis of Population-Based Data in England

Objective To assess whether changes in behavioural risk factors could explain rising cancer incidence in younger adults in England, and to evaluate the extent to which established and suspected risk factors contribute to these trends Methods and Analysis Cancer incidence data from national registries (2001-2019) identified cancers with increasing incidence in adults aged 20-49. Trends in smoking, alcohol, diet, body mass index (BMI) and physical inactivity were examined using national health surveys. Annual percentage changes quantified trends by age and sex. Population attributable fractions (PAFs) estimated the proportion of cancers attributable to risk factors and disaggregated attributable from non-attributable incidence rates. Results Eleven cancers with established behavioural risk factors showed rising incidence in younger adults. Similar trends were observed in older adults, except for colorectal and ovarian cancer, which increased only in younger adults. For some cancers, incidence increased more rapidly in younger than older adults. PAFs for younger adults ranged from 7% to 65% depending on cancer type. All risk factors except obesity showed stable or declining prevalence. For BMI-related cancers, both BMI-attributable and non-attributable incidence increased, though more slowly for the latter. For example, BMI-attributable colorectal cancer in younger women increased from 0.9 to 1.6 per 100,000 (APC 4.3%), while non-attributable rates rose from 6.4 to 9.6 (APC 3.2%). Conclusions Behavioural risk factors account for a substantial share of cancer burden but, apart from BMI, are unlikely to explain the rising incidence in younger adults. Findings underscore the urgent need to investigate emerging risk factors, while strengthening prevention efforts targeting known factors across all ages.