What’s behind the increase in cancers in younger adults?

The increase in cancer diagnosis amongst young people has been a hot topic for many years, with incidence rates increasing by around 6% since the early 2000’s (CRUK). The key question on everyone’s mind is WHY is the rate increasing? Enter an interesting study just published in BMJ Oncology, looking at whether trends in exposure to known risk factors may shed light on rising incidence in younger adults (defined as aged 20-49 years).

What did they do?

This was an ecological study examining cancer incidence data from the National Disease Registration Service for England over the last 2 decades (2001 - 2019) alongside the prevalence of established risk factors obtained from population-based surveys in England. 

Key findings

They identified 11 cancer sites with increasing incidence in younger adults that also had ‘established behavioural risk factors’. These sites were thyroid, multiple myeloma, liver, kidney, gallbladder, colorectal, pancreatic, endometrial, oral, breast and ovarian cancer. 

Their analysis suggested that combinations of modifiable risk factors such as consumption of red and processed meat, excess alcohol, physical inactivity, smoking, and low fibre intake and raised BMI could have contributed to a significant proportion of cancers in 2019. In particular for colorectal, endometrial, oral and liver cancers they estimated that combined risk factors may account for around 40-50% of the cases observed.

However, interestingly the study found that the majority of these risk factors were either stable or trending downwards in younger adults over the study period, meaning that they are unlikely to explain the rising incidence of cancer. 

Obesity was the notable exception with prevalence increasing for all adults, and the largest increases seen in younger women. Could this be a key cause of cancer at younger age? 

Population attributable fractions were used to estimate the proportion of cancers linked to the risk factors. The incidence of cancers attributable to raised BMI did increase over the period of the study, but this was far from the full picture. As highlighted in an associated BMJ news article, they estimated around 20% of the rise in bowel cancer that in younger women between 2001 and 2019 could be linked to the observed rise in BMI (BMJ 2026), and therefore there are likely to be multiple other contributing factors.

Limitations

This was an observational study, with significant potential for confounding. As discussed in the BMJ news article BMJ 2026, ‘BMI is an imperfect measure of obesity’, used as a surrogate marker for adiposity. It is unclear to what extent related factors such as metabolic dysfunction, diabetes, or inflammation may underly the observed association between raised BMI and cancer. 

Further, the authors noted difficulty with patchy data availability for some risk factors including physical activity and the inherent inaccuracy in self-reported surveys. They assumed a 10-year lag time between exposure and cancer, which has the potential to overlook risk factors with a longer run in.

Implications for practice

This study has highlighted obesity and obesity related conditions as one key area of focus for research in the worrying trend of cancer affecting younger adults, whilst acknowledging ongoing uncertainty about other risk factors and causes. 

Powerfully, the authors comment ‘Given the high prevalence of overweight/obesity, reducing their prevalence could substantially lower incidence (eg, ~20–30% for endometrial, kidney, liver and gallbladder cancers in younger women, ~20% for kidney and liver cancer in younger men, and ~15% for colorectal cancers in younger men or women).’

As GPs we can play a key role in supporting patients with overweight and obesity. 

If you want to learn more about the latest developments in medicine and increase your confidence in this complex and vital area, you can view our Hot Topics Managing Obesity and Overweight course on demand at a time that suits you..