The incidence of breast, bowel and other cancers is gradually increasing in people in their 20s, 30s and 40s.
What's going on here?
Over the past decade, the incidence of bowel cancer in the age group of 25 to 49 years has increased in 24 countries, including United Kingdom, United States, France, Australia, Canada, Norway and Argentina.
The preliminary results of this survey, presented by the international team at the International Union Against Cancer (UICC) congress in Geneva in September 2024, are both interesting and worrying.
图像来源，Maskot/Getty Images
Researchers from the United States Cancer Society (ACS) and the World Health Organization's (WHO) International Agency for Research on Cancer (IARC) looked at data from 50 countries to try to understand this trend.
In 14 of these countries, cancer rates have increased among younger people, while rates have remained stable among older people.
These findings are the latest in multiple studies that have shown a similar trend in increasing rates of multiple cancers among young people.
*unimaginable phenomenon*
Breast cancer is a striking example. According to a new report from the United States Cancer Society, breast cancer deaths have fallen by about 10% over the past decade, but the incidence has increased by 1% per year, especially among women under the age of 50, by 1.4% per year.
According to epidemiological surveys, this trend can be traced back to the 1990s.
One study found that between 1990 and 2019, the global incidence of early-onset cancer increased by 79%, while cancer-related mortality in younger people also increased by 29%.
Another report, published in The Lancet, noted a steady increase in the incidence of 17 cancers among the "Generation X" and "Millennials" in the United States.
This phenomenon has attracted so much attention that organizations such as the International Union Against Cancer have actively called for doctors to be vigilant to ensure that cancer symptoms in young patients do not go unnoticed.
"A doctor who listens to patients over the age of 60 complaining about constipation, feeling tired and bloated will pay more attention to these symptoms, whereas a young, active patient in his 30s may not pay much attention to these symptoms because they don't look like a cancer patient."
Sonali Johnson, UICC's director of advocacy·, said Sonali Johnson. "Doctors may blame these symptoms on irritable bowel syndrome or stress at work, so many patients have their symptoms ignored rather than being referred for blood tests or colonoscopy."
Cancer experts point out that diseases like pancreatic cancer, which are usually diagnosed in people in their 70s, are now dozens of years younger.
"It's not uncommon for me to see pancreatic cancer patients under the age of 40."
Eileen O'Reilly, a gastrointestinal onco·logist at Memorial Sloan Kettering Cancer Center in New York, says Eileen O'Reilly.
"It's almost every week, and it's scary. These people are in the prime of their lives, have just started a family, and have a bright future ahead of them. This has far-reaching implications for society. ”
Oncologists generally believe that cancer in young people is primarily related to genetic risk factors, such as BRCA1 and BRCA2 gene mutations in breast cancer. However, an increasing number of younger patients do not have obvious genetic factors.
O'Reilly points out that most of the early-onset cancer cases she sees have no obvious genetic explanation, and that young patients tend to have more aggressive tumors than those in their 70s, making the outcome of young patients even less optimistic, even if they are otherwise in good health.
"They are younger, healthier and generally better able to withstand the intensity of treatment, but some people have this highly aggressive pancreatic cancer that causes patients to debilitate quickly in front of us." She said.
"It's often incomprehensible to them and to us, because who would have imagined that a healthy 40-year-old would suffer from such a malignant disease?"
As this trend grows in focus, cancer experts are scrambling to figure out what is contributing to this phenomenon.
The authors of The Lancet note that if this trend continues, it could increase the burden of future health care and even reverse the public health advances in the fight against cancer over the past few decades.
图像来源，Getty Images
Some researchers have suggested that certain ingredients in ultra-processed foods may play a role in triggering inflammation and DNA damage in the colon.
*Reasons behind it*
Currently, the most intuitive explanations are obesity and metabolic syndrome, conditions that are associated with an increased risk of cancer because they trigger systemic inflammation and lead to dysfunctions of key hormone pathways.
A new study found that being overweight between the ages of 18 and 40 increases the risk of up to 18 different cancers.
The Lancet report also pointed out that 10 of the 17 cancers with an increase in cancer incidence among young people in United States were obesity-related cancers, including kidney cancer, ovarian cancer, liver cancer, pancreatic cancer, gallbladder cancer and multiple myeloma.
"The overall evidence points to lifestyle changes."
Shuji Ogino, a professor of pathology and epidemiology at Harvard University who has been studying the rising trend of early-onset cancers, said.
"Each of us has thousands of genetic variants, some of which slightly increase cancer risk, but when they are combined with environmental changes, the risk becomes even higher. We know that excessive sugar and processed foods, persistently high blood sugar, and insulin rejection increase not only the risk of diabetes, but also cancer. ”
However, obesity is not the only explanation. O'Reilly said many of the young pancreatic cancer patients she saw were normal-sized and had no obvious risk factors.
"What struck me was that many of the traditional risk factors that we think are mostly unrelated to these patients," she said.
"They look healthy, energetic and toned."
According to Ogino Shushi, this may reflect the emergence of new carcinogens that have not received enough attention before.
Although epidemiologists have long focused on the link between smoking and cancer, smoking rates have declined significantly in recent decades, with only one in five adults now using tobacco products globally, up from one-third in 2000, according to the World Health Organization.
Instead, Ogino argues that a much-overlooked correlation is the dramatic change in global sleep patterns over the past 50 to 100 years.
One study found that between 1905 and 2008, the average sleep duration of children and adolescents decreased by 60 minutes per night, while shift work increased in Australia, China, Japan, Europe, and North and South America.
A 2021 study using data from the United Kingdom Longitudinal Study on Ageing found an association between poor sleep quality and a higher risk of cancer. The database contains information on more than 10,000 people over the age of 50.
Some scientists even believe that modern people's long-term exposure to artificial light sources, such as street lights, cell phones, and tablets, may disrupt the body's biological clock, thereby increasing the risk of breast, colon, ovarian, and prostate cancers.
Some studies have shown that excessive exposure to light at night because of shift work may lower levels of melatonin, which may promote cancer growth.
"We were exposed to a lot of nighttime artificial light from a young age." Ogino Shushi noted.
"In Japan, many people stay up until midnight almost every night. Convenience stores that are open 24 hours a day (the popularity) of shift work are becoming more and more common. ”
At the same time, he said that many early-onset cancer cases are unlikely to be triggered by a single risk factor, but rather a combination of factors.
With lifestyle changes, many cancer scientists believe that the main driver of these diseases is the result of changes in various harmful substances in the gut.
图像来源，Getty Images
Some scientists believe that long-term exposure to street lamps or artificial light sources such as mobile phones and tablets can interfere with biological clocks.
*Gut Health and Antibiotic Associations*
In June 2023, colorectal surgeon Frank · Frissel of Christchurch Hospital in New Zealand issued a global call for colorectal cancer experts to increase research into the potential association between high microplastic intake and early-onset bowel cancer.
He published a paper entitled "Could Microplastics Be a Cause of Early-Onset Colorectal Cancer?" The paper argues that the increasing number of colorectal cancers in people under the age of 50 coincides with the rapid increase in microplastics in the environment.
He believes that these tiny plastic particles may damage the mucus layer of the intestine, which is supposed to protect the intestinal wall from various pathogens and toxins in food.
"Microplastics and nanoplastics may make the mucus layer somewhat permeable, like punching many pinholes in a condom." He said.
"If we can prove this, it could be related to particle size, as is the relationship between carbon particles and lung disease."
For now, this is still mostly speculation, but Frissell is far from the only scientist who has linked changes in toxins in the gut to a potentially carcinogenic process.
Other researchers believe that certain ingredients in ultra-processed foods, such as food colors and emulsifiers, may promote inflammation and DNA damage in the gut, although similar to microplastics, current evidence remains relatively limited.
Since the colon is connected to the stomach, the entire digestive system, and the immune system, significant changes in the intestine are associated not only with colorectal cancer, but also with a variety of parenchymal solid tumors, including breast cancer and blood cancer.
Overuse of antibiotics may also be one of the causes of early-onset cancer.
The study found that global antibiotic use has increased significantly over the past few decades, particularly among children under 5 years of age, from 9.8 per 1,000 population in 2000 to 14.3 in 2018.
Overall, global per capita antibiotic consumption increased across all age groups between 2000 and 2015, which O'Reilly sees as a key concern.
This can have negative effects due to the fact that antibiotics are able to destroy a large number of bacteria, which can significantly alter the microbiota of the gut.
Long-term heavy use of antibiotics has been linked to cancers such as lung cancer, lymphoma, pancreatic cancer, kidney cancer, and multiple myeloma.
"The bacteria in the gut were selected through some kind of Darwinian evolution, and they are part of the immune surveillance system that helps our immune system recognize abnormal cells and foreign substances and prevent the formation of malignant tumors." O'Reilly said.
"While we're not quite figured out, there is a hypothesis that more antibiotic use may result in immune surveillance not working as effectively as it should."
One potential consequence of antibiotic overuse is that killing commensal bacteria in the gut – these are the bacteria native to the gut – may provide space for harmful microbes to survive.
Over the past decade, Ogino and his global partners have published numerous studies showing that some opportunistic pathogens appear to be able to invade the gut and trigger cellular changes that increase the risk of cancer development.
Among other researchers, Ogino and others have found that a bacterium called Fusobacterium nucleatum may drive the growth of precancerous intestinal lesions and promote the development of more aggressive tumors.
Other studies have also shown that certain strains of E. coli not only promote cancer development, but also inhibit the body's immune response.
Similar to sleep and obesity, Ogino points out that the factors that contribute to early-onset cancer are multifaceted, and from childhood to adulthood, these factors may work together to gradually increase the risk of disease in young people.
He also points out that while most of us carry some form of E. coli, his research shows that when we consume a "Western diet" that is high in ultra-processed foods, the activity of these bacteria increases significantly, suggesting that diet also plays a key role in this.
At this time, we are still not completely sure why different populations develop early-onset cancers. But O'Reilly said scientists must study the phenomenon more deeply to avoid a possible global health crisis in the future.
"We urgently need more research to figure out what exactly happens in the early stages and what motivates these diseases to happen early," she said.
"I am very concerned to see the rising incidence of pancreatic cancer and other solid organ cancers among young people. For me, this is a looming public health crisis. ”