Are more young people getting cancer?
The majority of cancers occur among those over the age of 50. However, in recent years, researchers around the world including the UK, US, Australia and parts of Europe have reported a shift where more cancers are being diagnosed in people under 50. These are commonly referred to as ‘early-onset’ cancers.
This doesn’t mean cancer is suddenly common in young people. Age is still the most important risk factor for cancer overall. Although the average age of diagnosis for cancer overall differs by country, the median or average age of diagnosis in developed countries is above the age of 60. Average age at diagnosis also differs by where in the body the cancer develops, which is commonly referred to as ‘cancer site’ or ‘site-specific cancer’.
At the same time, evidence suggests that more new cases are being diagnosed among those younger than 50 for several site-specific cancers. Furthermore, incidence rates are higher among this group now compared with those who were in the same age group in previous decades. In short, we are seeing increasing numbers of some cancers among younger people.
To understand why this might be happening, World Cancer Research Fund International analysed how the absolute numbers of 12 site-specific cancers changed between 2000 and 2023 in the United States and the Netherlands, and 2021 and 2023 in England among those under 50 years of age. For each country, we also explored incidence rates for the first and last years – 2000 and 2023 for the US and Netherlands and 2001 and 2023 for England – for each site-specific cancer. Finally, we reviewed the published evidence related to what might be driving changes in the number of cases of cancer in the last few decades.
What do the numbers tell us about early-onset cancer?
By analysing the data, as well as identifying statistically significant trends over time, we were able to identify changes in the numbers of several site-specific cancers. By country and sex, the early-onset cancers that showed significant increases were:
US:
- Women: breast, colorectum, uterus, kidney, liver, pancreas, stomach
- Men: colorectum, kidney, pancreas, stomach
Netherlands:
- Women: cervix, colorectum, kidney, liver
- Men: colorectum, kidney, liver
England:
- Women: breast, colorectum, cervix, uterus, kidney, liver, pancreas, stomach
- Men: colorectum, kidney, liver, pancreas, prostate
We found further results that either showed non-significant changes (trends) in the number of cases or statistically significant decreased numbers.
Why are these increases happening?
The short answer is we don’t completely know yet. Further research is needed to understand the causes of increasing cancer cases among younger people, but we can hypothesise that multiple factors are likely interacting to create the changing trends we are seeing.
1. Changes in rates of modifiable risk factors
Our research shows that several modifiable behaviours and risk factors impact cancer risk. These include several risk factors that can increase an individual’s cancer risk including overweight and obesity, lower physical activity, and diets high in red and processed meat, fast foods, sugary drinks and low in fibre. While diets high in whole grains, fruit, vegetables and beans can lower risk. Our Cancer Prevention Recommendations outline habits that can be followed to reduce your risk of cancer.
Approximately 40% of cancers are considered preventable because they are attributable to modifiable behaviours (including smoking status, alcohol consumption, sun exposure, overweight and obesity, and physical activity levels). Modifiable risk factors refer to behaviours that, to a greater or lesser extent, can be changed by the individual.
As rates of these behaviours change in a population, so too do rates of cancer. This likely explains some (but not all) of the changes in the number of cases of early-onset cancer.
2. Environmental exposures and changes to the gut microbiome
While no single exposure explains the global rise in early-onset cancer, researchers suspect environmental changes across generations may be part of the picture.
Scientists are investigating whether long-term exposure to pollutants, chemicals, plastics, water and air pollution could be contributing to cancer risk. Researchers are also studying how the gut microbiome, the trillions of bacteria and microbes living in our digestive system, may be changed by our environment and how it impacts our risk of disease.
3. Better awareness and detection
Some increases in cancer cases may reflect better diagnosis. Compared with previous generations, younger adults are currently more likely to be aware of the signs and symptoms of cancer and are, consequently, more likely to seek out healthcare when they experience them.
This can help detect cancers earlier or identify cancers that may previously have gone unnoticed. However, researchers stress that improved detection alone does not explain all of the increase in new cases seen in the under 50s, especially for cancers where mortality is also increasing.
Are there biological mechanisms that explain increases in early-onset cancers?
Overweight and obesity are known to contribute to systemic inflammation within the body, as well as insulin resistance and hormonal changes that may increase cancer risk. It is also associated with an increased risk of type-2 diabetes which, in turn, is linked with increased cancer risk.
Many of these exposures now occur earlier in life and/or population-level rates of them have changed across the decades. This means that younger generations may be accumulating cancer risk for longer periods of time or in different ways compared with previous generations. For example, the World Health Organization reports that rates of overweight and obesity have risen sharply in recent decades: obesity rates have doubled among adults and quadrupled among adolescents since the 1990s, with 1 in 8 people now living with obesity.
Research reports that diet, antibiotics, pollution and other modern exposures may also alter inflammation and immunity and, as a consequence, cancer development. Overall, the biological mechanisms that underpin changing cancer risk in the under 50s is not clear, and further investigation is required to understand the full picture.
Are younger people now at high risk overall?
No – cancer is still less common in younger than older adults. What has changed is that, among those younger than 50, the number of some cancers have been increasing in recent decades. Our analysis of the data shows that some cancers that were once considered rare in younger people are now becoming more common.
What happens next?
Understanding early-onset cancers is now a major research priority.
Scientists are studying genetics, modifiable risk factors, environment, tumour biology and the microbiome to explain why younger generations are being affected differently to older ones. Given the pace of this work, current research will lead to better prevention, increased awareness, earlier detection and more personalised treatment in the not-too distant future.
Our funded research projects related to early-onset cancers
World Cancer Research Fund and its network of charities have been undertaking research to better understand how to prevent cancer for over 30 years. We will continue to fund research focused on understanding and preventing early-onset cancers.
To explore some of the hundreds of research grants that World Cancer Research Fund and Wereld Kanker Onderzoek Fonds has awarded you can search our grants database.
Current projects that are particularly relevant to early-onset cancers include:
- Investigating colorectal cancer in young adults: This study seeks to investigate the role of diet and nutritional factors in relation to colorectal cancer development in young adults by pooling together data from over 25 worldwide cohort studies.
- Early life infections: pathways to prevent adult cancers? This study seeks to investigate whether severe acute infections early in life are linked to risk of cancer in early adulthood.
- Impact of nutrition and exercise programme after cancer diagnosis: This study seeks to investigate the effectiveness of a comprehensive programme for people after cancer, which includes nutrition, exercise, sleep and stress management, and explores the use of technology such as smart watches.
How did we analyse the data?
To help us understand how the numbers of each site-specific cancer have been changing we descriptively analysed the data, undertook trend analysis and produced incidence rates.
Descriptive analysis
Descriptive analysis helps us to report (describe) the number of cancers occurring in a specific year and explore whether there are changes, patterns and trends in those numbers over time – in this instance between 2000/2001 and 2023.
Trend analysis
We also undertook trend-over-time analysis, called the Mann-Kendall trend test, to better understand if the increasing or decreasing numbers year on year were statistically significant – meaning that the results we are seeing are real differences and not happening by chance.
Incidence rates
We report age-adjusted incidence rates for 2000 and 2023 for the US and Netherlands. These let us compare the rates of each cancer for different years while taking into account the age mix of the overall population.
For the UK, age-adjusted incidence rates were not available for the under 50 population so we provide age-specific incidence rates for 2001 and 2023. This type of incidence rate accounts for the size of the age group over a particular time period, rather than simply counting new cases. Unlike an age-adjusted incidence rate, it does not take into account the age mix of the whole population.
