Australians aged in their 30s and 40s are experiencing unprecedented and in some cases world-leading rates of 10 different types of cancer — and scientists are desperate to understand why.
www.abc.net.au
Cancer rates in Australians under 50 are rising at a pace that's alarming doctors and scientists
By Norman Swan, Elise Potaka, Maddy King, Anushri Sood
Sun 6 Jul, 2025
Chris Burton was planning his wedding when he noticed he was bleeding after going to the bathroom.
He thought it was strange, but figured it was a one-off. Six weeks later, it happened again.
His GP referred him for a colonoscopy, and Mr Burton arranged to have the procedure after he and his wife returned from their short honeymoon.
The 39-year-old had advanced bowel cancer. The test results stunned him.
"That's probably similar to a lot of young people. Cancer's not at the forefront of what you think might be wrong with you," he says.
Australians aged in their 30s and 40s are experiencing unprecedented and in some cases world-leading rates of at least 10 different types of cancer — and scientists are desperate to understand why.
It's a question Mr Burton has struggled with since his diagnosis and one that's arrived at what should be a joyous time — the couple's about to have a baby, a little sister for their older daughter Isobel.
"That's the 3am thoughts that go through your head … have you done something to deserve it?" Mr Burton says.
"If there's not bowel cancer in your family, how come you've got cancer and how come you got it at a young age?"
No longer 'a disease of aging'
The technical term for this phenomenon is early onset cancer and it is rising steeply.
Data provided to Four Corners by Cancer Australia, the federal government's cancer agency, paints a concerning picture for young people.
Between 2000 and 2024 — in 30 to 39-year-olds — early onset prostate cancer increased by 500 per cent, pancreatic cancer by 200 per cent, liver cancer by 150 per cent, uterine cancer by 138 per cent and kidney cancer by 85 per cent.
Some increases, such as prostate cancer, might be explained by changes in the way they are diagnosed — but most cannot.
"There are approximately 10 [cancers] that have this increase to varying percentages," says Cancer Australia's chief executive, Dorothy Keefe.
"Cancer has traditionally been a disease of aging, and bowel cancer, breast cancer, lung cancer, they all increase with age.
"But over the last 20 years, there's been a real — it's small in absolute numbers — but it is a real increase in the number of younger adults developing these cancers."
Australia isn't the only country seeing higher rates of cancer in young people either. Large amounts of data from US cancer registries show an even more pronounced trend.
Philip Rosenberg, a leading cancer bio-statistician who recently retired from the US National Cancer Institute, says there is a clear difference when comparing cancer rates between generation X and baby boomers.
"There were really very notable differences, for colon, rectum, thyroid, and pancreas, and as well prostate for men and ER (oestrogen receptor) positive breast cancer for women," Dr Rosenberg says.
"Overall, it's about half of the different cancer types."
Worryingly, Australia is a world leader when it comes to bowel cancer.
Since the year 2000, rates of bowel cancer in 30 to 39-year-olds have increased by 173 per cent — and the stage the cancer is at when diagnosed is often late, meaning it is more likely to have spread and harder to treat.
'It's like a fingerprint'
Dan Buchanan, an associate professor at the University of Melbourne who is part of the Collaborative Centre for Genomic Cancer Medicine, is trying to find out why Australia's bowel cancer rates are so high compared to the rest of the world.
"The statistics around early onset bowel cancer are really alarming," Dr Buchanan says.
It's a shift he can see just by looking at a tumour's DNA mutations.
"In the youngest group of people that developed early onset colorectal cancer, we're seeing a much higher proportion that have a particular type of DNA damage pattern," he says.
That generational difference is so pronounced, he says he can tell whether a person is young or old from their tumour's DNA.
"It's like a fingerprint; something's happened. It's dramatic," Dr Buchanan says.
He says it suggests that there are factors or "exposures" that are contributing to an earlier diagnosis age for a group of colorectal cancers.
What is causing this generational damage however is less specific — but scientists are starting to get a clearer understanding.
Different cancers, different causes
It is fiendishly difficult to tie down the exact causes of any cancer, even though we know all cancers are caused by genes.
There are inherited genetic mutations that cause cancer in their own right — for example, the BRCA genes for breast and ovarian cancer, and the Lynch Syndrome for bowel cancer.
But young people behind this rise in early onset cancers do not carry such genes.
Instead, most experts believe toxins or toxic influences in the world around us are interacting with genes to cause malignant changes.
In other words, you might unknowingly carry a gene that's only altered when you're exposed to a particular chemical, whereas someone else who doesn't have that version of the gene would be unaffected.
"Cancer is not a single disease, it is many different diseases," explains associate professor Gianluca Severi, a senior cancer epidemiologist based at the National Institute for Health and Medical Research (INSERM) in Paris.
"Within a disease that is called breast cancer, there are actually many diseases, but we know that there are different subtypes of breast cancer.
"It's important because that means that the causes of these different types of cancers are different."
The name for the physical, chemical, psychological and social exposures in the environment which can affect human health is the exposome. Dr Severi is investigating such exposures in relation to cancer.
In May, an international group of researchers announced a massive undertaking called the Human Exposome Project, which is documenting and studying these exposures.
"It basically encompasses all the environmental factors but also lifestyle and their connections and interactions to try to explain the causes of different diseases," Dr Severi says of the project.
But the challenge to determine when the exposures occurred is another variable which makes tracking cancer causes hard — because tumours can take decades to develop.
What's changed?
To get a better understanding, researchers say we need to look at the environment when people in their 30s and 40s today were children or in utero.
That means the environment — or the exposome — between the 60s and 90s is crucial to understanding this puzzle.
For instance, it was during those decades when the childhood obesity epidemic began.
"It is very likely that childhood obesity and increasing obesity in young adults is part of the cause of this increase in early onset cancers," Dr Severi says.
That connection is something liver specialist professor Simone Strasser finds in her patients. Primary liver cancer — or hepatocellular carcinoma — is another of the fast-rising early onset tumours.
"The problem with obesity and diabetes driving liver disease is that we are seeing this in children and adolescents," she says.
"Then 20 years of that history … you're still a young person at the time that you're running into problems from that and developing cirrhosis and liver cancer."
There is also evidence that our gut bacteria — our microbiome — may have changed too, through antibiotic use, and eating ultra-processed foods.
Caesarean section rates were also increasing during these decades, meaning babies didn't acquire the same microbiome as those born vaginally. That could potentially affect their immune system development.
These changes could have made our gut more vulnerable to dangerous bacteria and is a major focus for Dr Buchanan.
"We have lots of bacteria in our gut … and it's that balance between good and bad bacteria that creates a healthy state," he says.
"We think that exposures or environmental toxins may change that balance between good and bad bacteria, allowing some not so friendly bacteria to produce toxins that may damage our DNA."
Research is finding that exposure — probably early in life — to a toxin from a bowel bug called E. coli could be driving some of the mutations that Dr Buchanan is seeing in his bowel tumour samples. He's convinced it's one of the causes.
"The story for that particular gut bacteria has gone well beyond an association into causation," he says.
But there are other toxins which scientists believe are affecting our genes — and they aren't from bacteria.
Exposure to the unfamiliar
Since World War II, we have been exposed to more and more chemicals and plastics in our day to day lives.
Christos Symeonides is a paediatrician who studies chemical and microplastic exposures through his work at the Minderoo Foundation.
"We are exposed to a broad universe of synthetic chemicals … that our biology isn't familiar with, and that has left a great deal of uncertainty," Dr Symeonides says.
"Within the universe of plastic chemicals, we're looking at the last academic count at about 16,000 chemicals that are used or present in plastics."
Dr Symeonides says only one-third of those chemicals appear to have been evaluated for their potential hazard, and about "75 per cent" of those evaluated have been identified as hazardous.
"But there's a limit to which that tells us about what they'll do in our full complex biology of the human body," he says.
For the two-thirds of chemicals that haven't been tested, Dr Symeonides says their hazard rate can't be assumed to be the same — but that doesn't mean they're safe either. It's one of the problems he has with the way chemicals are regulated.
"It seems that the system is currently based on exactly that assumption, that until you establish and prove harm, a chemical is considered to be safe, whether you've looked for harm or not," he says.
Dr Symeonides has reviewed the evidence and concluded that only five classes of chemicals — comprising fewer than 100 individual chemicals in total — out of the thousands have been studied to the depth required to find human effects if they exist.
"For all five of those classes, there were serious health impacts with strong evidence of a link between exposure and those health impacts," he says.
Concerns about the health effects of plastics are nothing new. In fact, when generation X were babies or in utero, we already knew that some of these chemicals were harmful.
"There's a group of chemicals that had a use in plastic as flame retardants but had much broader use that we now regulate very tightly called PCBs or polychlorinated biphenyls," Dr Symeonides says.
There's also another group of persistent chemicals, known by their generic name of per or poly fluoroalkyl substances (PFAS) that are suspected of causing harm.
These chemicals can be found in non-stick cookware, food packaging, and even some cosmetics, and are often called "forever chemicals" because of their environmental persistence.
One of them, called PFOA, has been associated with kidney cancer, and Dr Symeonides says there is also a strong link between exposure to PFOA and breast cancer.
A ban on the industrial use of PFOA is now in force in Australia, but its effects could be with us for years to come due to its persistence in the environment.
Does the next generation have the answers?
The ORIGINS project in the northern suburbs of Perth aims to answer some of these questions for today's children.
They are following the health and wellbeing and recording medical observations of 10,000 children. In fact, the researchers at Joondalup Health Campus and The Kids Research Institute Australia are measuring these families' exposome as best they can.
"There's this whole concept of developmental origins of disease where things that happen early in your life do impact on people later on," says professor Desiree Silva, the project's co-director.
"The ORIGINS study will help to understand the microbiome because we are collecting samples in pregnancy in mums, and then we're collecting samples in those children.
"Because we've got longitudinal bio samples and data, we can actually look at that environmental impact on what may be the causal pathways of cancer."
It will be many years before ORIGINS has answers for today's kids. Meanwhile, the generations before them are confronting the reality of living with cancer.
For Mr Burton, he's focusing on his family and their future. His wife Ali gave birth to a healthy baby girl at the end of June, just three days after his latest surgery. All are doing well.
"It's a stormy dark period, but you know, it's possible to survive," he says.
"I like to think about us growing old together, raising the girls, and we can look back on this time period and think, 'That was really hard, but we made it through.'"
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