In 2022, around 16% of the 20 million people with cancer worldwide were under 50. Cancer has always been markedly more of an older person’s disease, says Lynn Turner, director of research at Worldwide Cancer Research. But between 1990 and 2019, the incidence of the disease in under-50s rose by 79%, according to research published in the British Medical Journal in 2023. That short timeframe means the rise cannot be explained by genetic factors, according to Tracey Woodruff, director of the University of California, San Francisco’s programme on reproductive health and the environment.
Many of these “early-onset” cases are happening in wealthier countries, says Kathryn Bradbury, senior research fellow at the University of Auckland’s school of population health. The rates are striking because younger populations are mainly non-smokers, says Mary Beth Terry, a professor of epidemiology at Columbia University. About two-thirds of cancers in under-50s occur in women, she adds.
In 2019, some of the most common cancers in under-50s were colorectal, breast and skin cancer. The early-onset cancers that increased the fastest between 1990 and 2019 were prostate cancer and cancers of the nasopharynx, or windpipe. Breast, stomach and bowel cancers – among others – were linked with some of the highest death tolls.
Colorectal: processed meat and ultra-processed foods
In 2024, Cancer Research UK and several other organisations funded a research project called Prospect looking into the global rise in colorectal cancer in under-50s. The trend is particularly concerning in England, where rates seem to be rising faster than anywhere else in the world except for New Zealand, Chile and Puerto Rico. Prospect will investigate a variety of risk factors, including poor diet.
One aspect of diet that is a concern is high consumption of processed meat, which is a “Group 1” carcinogen, meaning there is sufficient evidence to conclude it causes the disease in humans. The term “processed” describes meats that have been salted, smoked, fermented or cured to boost their flavour and longevity – for example, ham and bacon. Meat consumption in general has grown substantially in the global diet over the past 50 years.
Processed meats are high in compounds called nitrates and nitrites, which preserve them for longer. When these compounds get broken down in the body, they can damage cells in the bowel, according to Sophia Lowes, senior health information manager at Cancer Research UK. But while there has been evidence of this mechanism in mice and rats, it has been difficult to show the same in large human studies, says Marc Gunter, chair in cancer epidemiology and prevention at Imperial College London’s school of public health.
Certain methods for cooking processed meats – such as grilling at high temperatures – can release chemicals called heterocyclic amines and polycyclic amines, which also trigger cell damage, Lowes says, adding that it is difficult to establish a clear link between any one food item and cancer because dietary studies often rely on self-reporting. “What we think we eat and what we actually eat are two very different things,” according to Turner at Worldwide Cancer Research.
Another potential dietary risk factor is ultra-processed foods (UPFs), which make up 50-60% of daily energy intake in some high-income countries. They are made with ingredients rarely used in home cooking that are then processed further through fractioning, hydrogenation or adding flavours and colours. Common UPFs include fizzy drinks, ready meals and sweets.
One large study in the US found that men who ranked in the highest fifth for UPF consumption had a 29% greater risk of developing colorectal cancer than those in the lowest fifth.
But it’s unhelpful to discuss UPFs as a single group because the term covers so many different foods, Bradbury at the University of Auckland says. Wholemeal bread from the supermarket shelf is classed as a UPF because it is industrially produced – yet it’s rich in fibre and wholegrains, Gunter says. The risk seems to lie with specific ingredients found in certain UPFs.
One ingredient that has been investigated for a link to cancer is aspartame. The low-calorie sweetener is 200 times sweeter than sugar and commonly used in diet soft drinks and low-sugar yoghurts. There have been some animal studies that suggest aspartame has certain “pro-cancer properties” but the conclusion so far is that there is no “definitive evidence” of carcinogenicity in humans, Gunter says.
Researchers are also looking at E numbers – additives that serve to change food flavour, colour or texture – but this is an area where “there are still a lot of unknowns”, Gunter says.
In the US study, diets higher in sugar-sweetened beverages and ready-to-eat meat, poultry and seafood products were linked with an increased risk of colorectal cancer in men. For women, the risk was greater with diets high in ready-to-eat or heatable products.
Breast: reproductive factors and forever chemicals
The rise in breast cancer in under-50s is not a new trend, but the pattern in recent decades is notable because it doesn’t seem to be accounted for by the usual risk factors for cancer, such as obesity, according to Terry at Columbia University.
Obesity rates in adults worldwide have more than doubled since 1990. Extra fat can increase levels of growth hormones and inflammation, says Lowes. These signals tell cells to divide more often, increasing the chances of more than a dozen types of cancer.
Excess fat can also amp up certain sex hormones after the menopause, raising the risk of breast cancer. But this doesn’t explain the rise in cases in under-50s, Terry says.
One idea is that the rise in early-onset cases could be linked with a global decline in fertility because giving birth by a certain age and breastfeeding are thought to be protective against breast cancer. Having children before the age of 30 is “generally accepted” as reducing risk of the disease, says Hannah Moody, director of research and engagement at Breast Cancer UK. The first full-term pregnancy permanently changes a woman’s breast tissue in a way that makes it less vulnerable to cancer.
Furthermore, every 12 months a woman spends breastfeeding cuts her risk of breast cancer by about 4%, according to a study published in Cancer Medicine. This means that women who have multiple children and breastfeed them all could have a significantly lower risk.
The protective effect of breastfeeding is not fully understood but is thought to be linked with prolonged exposure to the sex hormone oestrogen, which affects how often cells divide, Moody says. Breastfeeding may reduce the amount of oestrogen circulating in the body.
But there is a “very high increase” in early-onset breast cancers even in countries that have high fertility rates, so reproductive factors alone can’t explain the trend, according to Terry.
Another explanation is exposure to per- and polyfluoroalkyl substances (PFAS), also known as “forever chemicals”. This group of thousands of compounds make products resistant to water, stains and heat, and are found in everything from cosmetics to food packaging and cookware.
Forever chemicals act as endocrine disruptors by increasing the levels of oestrogen in the body or mimicking the hormone, Moody says. Exposure to these chemicals may trigger a “lifelong impact” in utero and during early childhood, adolescence or pregnancy – life stages when cells are dividing rapidly, says Rainbow Rubin, director of science at Breast Cancer Prevention Partners.
Most PFAS have never been tested so their effect on human health is still unknown but research suggests that a few of them could raise the risk of breast cancer, Moody says. One meta-analysis of eight studies in 2022 showed a positive correlation between breast cancer and two types of PFAS called perfluorooctanoic acid (PFOA) and perfluorohexane sulfonic acid (PFHxS).
PFOA is one of the “original” forever chemicals at the heart of the PFAS water pollution scandal in the US. The Group 1 carcinogen is now in effect banned in the US and EU.
But most people still have trace amounts of PFOA in their blood owing to the compound’s longevity and its use over decades. “The carbon-fluorine bond in PFAS is one of the strongest in chemistry – that’s why they persist in the environment and our bodies for so long,” Rubin says.
Since the water pollution scandal, chemical manufacturers have switched to making new types of PFAS such as PFHxS, which are now in the environment at higher levels. Research published in September found PFHxS is associated with higher breast density, which is a risk factor for breast cancer. The compound was effectively banned in the UK in 2023. It will take “a while to figure out” which of the other newer PFAS are the most harmful, Rubin says.
Skin cancer: UV damage and diagnostic processes
Skin cancer is one of the most common cancers in under-50s, but it is not one of the fastest growing globally. The pool of data for certain types of skin cancer is small and countries record cases in different ways, but there has been a rise in early-onset cases in the UK and US.
The main risk factor for skin cancer is sunburn, says James Larkin, consultant medical oncologist at the Royal Marsden hospital’s skin and urology units.
Sunburn is caused by too much exposure to ultraviolet (UV) radiation, and is mostly driven by shorter wavelength UVB rays. UVA rays – which have a longer wavelength and can penetrate deeper into the skin – can also trigger skin inflammation and damage.
UV radiation damages DNA, which in turn triggers genetic mutations that lead to abnormal protein function, turning cells cancerous, Larkin explains. Campaigns to educate the public on the dangers of UV have been around for decades in many high-income countries, advising people to seek shade when the sun is strongest, apply and reapply sunscreen and wear protective clothing.
“The question is to what extent are people compliant with the knowledge? And I’m not really sure there’s high-quality data about whether they’re taking the advice seriously or not,” Larkin says.
Turner says: “There’s a lot more information out there about skin awareness but that doesn’t reach everybody, and some of the damage has been done decades ago.”
People between the ages of 15 and 24 are less likely to use sunscreen and sun protection methods but they also tend to spend more time indoors, says Catherine Olsen, senior research officer at the QIMR Berghofer Medical Research Institute’s cancer control group in Brisbane. In the Nordic countries, young women are also more likely to use tanning salons, she adds.
Meanwhile, some researchers believe there is an overdiagnosis of melanoma skin cancer in countries such as the US, supported by the fact that death rates remain similar despite a higher number of cases. The theory is that more skin screening tests, combined with lower bars for performing biopsies and reduced thresholds for labelling a lesion as cancerous, are leading to false positives.
With skin lesions at earlier stages, even well-trained dermatopathologists can find it difficult to tell if something is a cancer or not, says Marianne Berwick, distinguished professor at the University of New Mexico’s comprehensive cancer centre. The accuracy of a diagnosis also depends on how much of the lesion is removed and how well it is excised, she adds.
Regardless of cancer type, people can cut their risk by stopping smoking, reducing alcohol, maintaining a healthy weight, eating a balanced diet and staying safe in the sun, Lowes says.
