As cancer diagnoses in the under-50s soar, researchers are focusing on environmental as well as dietary causes – including a possible link between microplastics and bowel cancer, writes Sarah Catherall.
When David Shorter was diagnosed with aggressive stage four colorectal cancer early last year, the now 44-year-old looked back on his life searching for clues on what caused it. The Aucklander was fit and healthy enough, with no family history of bowel cancer. So, like many other cancer patients, he looked for signs of environmental causes.
Did six months working in a boatbuilding yard with chemicals spraying around him when he was 19 contribute to the growth of a tumour in his gut? Or was it the fact he was born nine weeks premature by caesarean?
At the time of diagnosis, he admits his diet “could have probably been better’‘, but he didn’t drink much alcohol and had never touched a cigarette.
The IT specialist had done enough reading on microplastics, too, to ponder if the plastic drink bottles and cooking ladles might have contributed to his cancer – along with other microplastics he might have ingested. He went through his kitchen and threw them all out. “I never had a medical issue before this. It came as such a shock. I guess the only thing is my diet could have probably been better,” he says.
He was speaking from the side of a swimming pool as he watched his children, aged 9 and 7, at swimming lessons. A surveillance scan in January found a cancerous lymph node in his liver, which was removed. Since then he has had two of six rounds of folfox ‒ a chemotherapy regime used to treat mestatistic bowel cancer. In palliative care since his diagnosis, Shorter is determined to spend as much time as he can with his family.
“My message is don’t wait until you’re terminally ill to prioritise what is important.
“Also, be your own health advocate. I had strange bowel symptoms for about a year but I put it down to being over 40 and maybe my digestive system was changing. I’d encourage anyone to go and see a doctor, no matter your age, and definitely get a colonoscopy, and I’d also encourage people to talk about their bowel motions.‘’*
Cancer under 50
Many cancers are rising in the under-50s and scientists and doctors around the globe are trying to work out why. Globally, diagnoses and deaths related to early-onset cancers ‒ affecting patients younger than 50 ‒ rose by 79% and 28% respectively from 1990 to 2019, according to a recent study published in the medical journal BMJ Oncology. Cancers with the highest death tolls were those of the breast, windpipe, lung, bowel and stomach.
The American Cancer Society says the under-50s are the only age group with a rising risk of developing 17 different types of cancer, and 12 of these are obesity-related. Nine of the cancers increasing in young people had been declining in older generations: estrogen receptor-positive breast cancer, cancers of the uterus, bowel, stomach, gallbladder, ovaries, testicles and anus, and Kaposi’s sarcoma, a form of blood cancer, in men.
Colorectal (bowel) cancer is the third most common cancer worldwide (1.9 million cases in 2020) and is currently New Zealand’s second deadliest cancer, behind lung cancer.
A soon-to-be published report co-authored by Christchurch colorectal surgeon Professor Frank Frizelle has found four cancers rising in young adults in New Zealand: colorectal, prostate, breast and uterine. Obesity, or excess weight, is the main cause with uterine cancer.
Globally, scientists and cancer specialists talk about a changing birth cohort. In lay terms, the risk of getting cancer before your 50th birthday has risen each decade in those born since 1960.
Colorectal cancer has jumped 26% per decade in New Zealanders under 50 since 2000, while rates dropped for over-50s. For Māori under 50, it rose 36%, says Frizelle.
“In disease terms, that’s like a Ferrari,” he adds, regarding the speed of change.
Focus on microplastics
A theory gaining traction is that what we do in our childhood and young adult years may trigger cancer decades later. There’s concern that early environmental exposures – diet and lifestyle and possible carcinogenic influences – particularly if prolonged, could play more of a part than previously thought, which is why David Shorter is now looking back on his entire life.
His oncologist has said there’s no genetic reason for his stage four cancer, though his younger brother and sister have both had colonoscopies since his diagnosis and polyps were found and removed.
One of the theories being researched by Frizelle and his team at the University of Otago’s Christchurch campus is that microplastics could play a part in rising colorectal cancer rates in the under-50s.
Frizelle has spent the past 25 years researching sporadic colorectal cancer, and in the last decade has been looking at it in young adults (when not caused by inherited genes or a previous inflammatory bowel disease) trying to work out what causes it.
His preliminary view is that microplastics and the much smaller nanoplastics could be interfering with the interaction within the gut microbiome (the colony of microbes that live in the digestive system).
Microplastics are everywhere – they’re in the air we breathe, in the oceans and waterways, and in our foods, or wrapping store-bought products. In global studies, microplastics have been found in faeces, placentas, lungs, liver, breast milk, urine and blood, and even in cancer tumours.
A study by researchers at Columbia and Rutgers universities in the US showed an average litre of bottled water contains almost a quarter of a million nanoplastic fragments.
Frizelle, a medical adviser for Bowel Cancer New Zealand and internationally recognised expert on diseases of the colon and rectum, says: “The day you’re born, someone sticks a [plastic] bottle in your mouth. The amount of microplastics we consume in a lifetime is huge – from the toys you suck to the [plastic] wrap on your food. The numbers are huge, and microplastic consumption is a relatively new phenomenon.‘’
Colorectal cancer is now divided into early onset and old (over-60s) as they’re quite distinctive diseases. In older colorectal cancer patients, there are typical causes: red meat, processed food, being overweight, smoking, alcohol and lack of exercise. The cancers also present in different parts of the bowel. But, says Frizelle, in the under-50s where tumours are being found in the colon and rectum, there’s “plenty of data” to show this cohort usually don’t eat as much red meat or processed foods and are more likely to be healthier. Like David Shorter, they shouldn’t get tumours. Younger patients are also more likely to be diagnosed late ‒ a third of colorectal cancer in the under-50s are detected at stage four of the disease, says Frizelle.
“All those risk factors that older people have had, it’s not the same thing driving this,‘’ he says, having recently diagnosed cancer in a healthy 28-year-old who had had no previous bowel problems.
“We’re talking about those born since 1960. Our genes haven’t changed since then. What’s changed is the environment. We’ve been looking to see the model between the bugs, the food and the mucus. What’s changed in that to alter the risk of bowel cancer?”
Ultra-processed foods have been shown not to be a factor in early onset bowel cancer, he says. “The first 30 years of life, what you’re exposed to, sets us up. Twin studies have shown that. Whatever it is, it’s happening early.”
Frizelle and others studied populations in Sweden and Scotland and found the same thing – while their rates of colorectal cancer were respectively rising (Sweden) and stable (Scotland) in the over-60s, both countries along with New Zealand were experiencing spikes in colorectal cancers in younger adults.
In a paper he co-authored, The incidence of early onset colorectal cancer in Aotearoa New Zealand: 2000-2020, researchers pointed to many environmental factors: caesearean delivery, formula feeding, antibiotics, monosodium glutamate (MSG), the Western diet, ultraprocessed foods, corn syrup and synthetic food dyes.
He cautiously also points the finger at microplastics, and says studies suggest that when microplastics get into the body, they can damage the mucus lining that protects the bowel and act as a pathway, carrying bacteria and toxins to the bowel lining. The bowel is then more vulnerable to damage from pathogens, and in some patients, cancerous cells can take off.
“Micro- and nanoplastics are not toxic in themselves and are not causing cancer in themselves. It’s the effect they have that is important. We think they have potential to disrupt the mucus protection layer, allowing more toxins to get to the bowel.”
His team is now hoping to get ethical approval to assess plastic load in colorectal cancer patients. “Most people would probably be keen to find out.‘’
He’s not alone in following the microplastics theory, and other papers have linked microplastics with interfering with the gut microbiome. For example, a 2024 study published in Frontiers in Cellular and Infection Microbiology says microplastics have been shown to accumulate in the gastrointestinal tract, disrupting the gut microbiome and causing an imbalance between beneficial and harmful bacteria. This disruption has been linked to systemic inflammation and chronic diseases.
While packaging may, in time, prove to be an under-appreciated risk factor for early onset colorectal cancer other practitioners take a more cautious approach.
Professor Chris Jackson, a Dunedin oncologist with a special interest in gastrointestinal cancers, points to more general risks of Western diets and modern life.
In a paper he co-authored, Changes in colorectal cancer incidence in seven high-income countries: a population-based study, Jackson pointed to excess body weight, red and processed meat, alcohol, smoking, cooking at high temperatures, fatty diets and lower activity and fibre intake for the rise in young adult colorectal cancer.
“Evidence also suggests that antibiotic use during childhood, which alters the gut microbiome, could be associated with a rise in paediatric-onset inflammatory bowel diseases, which could eventually increase the risk of colorectal cancer,‘’ the paper says.
Uterine cancer
Another cancer increasing in young adults is uterine cancer, and it is almost wholly linked to obesity. Professor Andrew Shelling, of Auckland University, says uterine cancer is the most weight-related cancer, with obese women having 3-7 times the risk of other women, and particularly high rates of the cancer in young Pacific women.
Shelling, co-director of the university’s Centre for Cancer Research ‒ Te Aka Mātauranga Matepukupuku, pulls up a paper that found 39% of the women diagnosed with uterine cancer before their 50th birthday were Pasifika, compared with 29% Māori, and 14% Pākehā (Asian women weren’t counted). Of the 96 Pacific women younger than 50, 87 were obese or extremely obese.
Calling for more public awareness and a public health campaign, Shelling says a woman with a BMI greater than 40 has the same chance of getting endometrial cancer (the main type of uterine cancer) in her lifetime as a smoker has of getting lung cancer.
“Fat tissue increases oestrogen, stimulating abnormal cell growth in the uterus. Obese women have a higher risk of recurrence and worse survival rates.‘’
Shelling is also interested in the microplastics research, and says, “The microbiome is also relevant for all other cancers as well, and microplastics seems to be a new and emerging player.‘’
Long-term exposure
At Harvard University in the US, a team of molecular pathological epidemiologists are analysing bowel tumour tissues across all ages and these also point to early and long-term diet and environmental exposures for the spike in early-onset cancers. Professor Shuji Ogino is involved in a longitudinal study funded by the US National Cancer Research and the Cancer Research UK.
The Harvard team has, since the mid-1970s, followed 280,000 people, who were in their 30s to 50s when they were recruited. When colorectal (or bowel) cancers began showing up in some, they started studying tumour tissues. Some apparent risk factors for under-50s colorectal cancer so far include a high-fat, high-sugar, processed Western diet, developing insulin resistance (also linked to poor diet) and having a particular type of E-coli bacteria in the gut. For their latest study, co-funded by Cancer Research UK, Ogino and his colleague, Dr Tomotaka Ugai, brought in a team of experts to look across 14 cancer types. They found 12 that seemed to be increasing in the under-50s, including eight related to the digestive system.
Ogino tells the Listener by Zoom that those 12 include cancers of the head and neck, esophagus, stomach, liver, bile duct, gallbladder, pancreas, colorectum – along with breast, uterine body, kidney and certain blood cancers, which are becoming more common in young adults.
He expects colorectal cancer in the under-50s to reach 20% in the near future.Like Frizelle, Ogino talks about the birth cohort effect. “Since 1950, we found that each successive generation has a higher risk of early-onset cancer. Someone born in 1960 has a higher risk than someone born in 1950, and someone born in 1970 has a higher risk than someone born in 1960. It’s just continuing.”
Again, this is most obvious in bowel cancer, which Ogino calls the “spearhead’’ for the early-onset increase. He says it wasn’t until the mid-1990s that scientists became aware something was changing, as cancer used to be an older person’s disease. Ogino blames modern life: processed diets, sugar, sedentary lifestyles, drugs, screen time, chemicals, herbicides and pesticides, and yes, possibly microplastics.
One in five New Zealanders are going to get bowel cancer before they’re eligible for screening.
“We can’t exclude microplastics but they can’t explain everything,” he says.
“People used to be starved to death, but now we can eat as much as we want. It’s likely that all these risk factors work together.‘’
Part of the problem is that when someone is diagnosed with cancer, everyone looks at what’s happening now: what are they eating, what’s their activity and lifestyle like, rather than what they did decades ago.
Just as Shorter has looked back at his earlier life, Ogino says, “Nobody asks, ‘What did you eat as a baby? Were you breastfed and did your mother smoke or drink when she was pregnant?’
“I’m now living a healthy lifestyle but when I was a child, my parents gave me some drink with lots of sugar. I avoid sugar now, but 30 years ago I had a lot.”
Ogino stresses it’s important to change bad habits no matter what your age is. He points to the country of his birth, Japan, where early-onset cancers aren’t rising at the same rates, especially digestive cancers in younger men.
Japan is one of the only high-income countries where people don’t typically eat a Western-style diet. South Korea, meanwhile, is experiencing the same early-onset cancer spike as Western countries: it’s genetically and economically similar to Japan, but citizens are more likely to eat unhealthy Western foods.
Lower screening age
Cancer is New Zealand’s No 1 killer. In 2022, cancer caused 108 deaths per 100,000 people, well ahead of ischaemic heart disease at 42.2 per 100,000. But for Māori, the picture is much worse: with 169 cancer deaths per 100,000 and 68.4 for ischaemic heart disease.
However, survival rates are improving for some cancers, partly because of nationwide screening programmes. The evidence for colorectal cancer screening is so conclusive that the Bowel Cancer Foundation and others are concerned the government has ditched plans to lower the screening age from 60 to 45 to match Australia – which was National’s pre-election promise.
Instead, Health Minister Simeon Brown lowered the age from 60 to 58, opening it up to 120,000 more New Zealanders, but not going far enough, say critics. Brown also canned the previous government’s plan to lower the screening age for Māori and Pacific people to 50 in recognition of their greater risk of developing bowel cancer younger.
Nobody asks: what did you eat as a baby? Were you breastfed and did your mother smoke or drink when she was pregnant?
“One in five New Zealanders are going to get bowel cancer before they’re eligible for screening and that rises to one in three for Māori, so you’ve got a very significant problem there,” says Bowel Cancer New Zealand chief executive Peter Huskinson. He says the current screening programme is catching cancer earlier and detecting pre-cancerous polyps, which has led to a drop in colorectal cancer deaths in the over-60s.
Other countries are lowering the screening age, concerned about the rise in early-onset colorectal cancer. The UK screens from age 50. “It becomes cost-effective to screen younger and you’re saving lives,” says Huskinson. “The key thing is catch it early and there’s a 90% survival rate. Only 10% of stage four patients survive after 10 years.”
Jackson also wants the screening age dropped to 50, while Frizelle argues it should be 35 for Māori and 45 for others.
Risk still low
Jackson says the “absolute risk’’ of a New Zealander under 50 getting colorectal cancer is still very low – about eight in every 100,000 compared with 133 per 100,000 aged 50-79.
The colonoscopy service is already stretched, and more staff and resources would be needed to cope with the number of tests for those with symptoms if the age was lowered to 50: “We would need significant investment in colonoscopy capacity.”
While the worldwide quest continues to find out why some cancers are rising in younger people, there are exciting developments in immunotherapy and cancer-vaccine research.
Two huge Cancer Research UK -backed international projects are under way to find an ovarian cancer vaccine (now in pre-clinical stages) and a lung cancer vaccine, which is about to be trialled in the UK on people at high risk of developing lung cancer, or those in remission. Another trial is developing immunotherapy vaccines for patients with existing tumours.
Meanwhile, Jackson says cancer prevention messages haven’t changed. “We have an obesity problem in New Zealand and we need to address this. The small number of people who still smoke should join the large number of people who don’t. Get vaccinated against HPV, minimise your alcohol and slip slop slap and wrap for skin cancer. Also exercise. Exercise is a key prevention measure for cancer.‘’
Agreeing there are likely to be environmental causes driving the global spike in young adult cancers, he adds: “The other issues such as the gut microbiome, antibiotics, nitrates in water, and the very new theory on microplastics remain areas of discovery and research.”