Cancer is increasing in young people and we still don’t know why

Attempts to uncover the reasons for the increase in cancer among young people have raised more questions than answers. One study found that rising obesity rates could explain a small part of the increase, but it’s far from a complete explanation.

“Our main conclusion is that, although BMI [body mass index] This is our best indicator, but a large part of these increases still remain unexplained,” says Montserrat Garcia-Closas of the Institute of Cancer Research (ICR) in London.

Around the world, a number of studies have found that cancer rates among adults under the age of 50 are increasing. Since the 1990s, the rate of bowel cancer has increased by about 50 percent in several countries, including the United States, Australia and Canada.

To try to understand why, Garcia-Closas and colleagues looked in detail at cancer trends in England and compared them to demographic trends in risk factors such as obesity. Based on data through 2019, they found that 11 types of cancer are increasing among people aged 20 to 49, with the most common being breast and bowel cancer. Others include liver, kidney and pancreatic cancer, with an increase rate ranging from 1 to 6 percent per year.

For nine of these 11 cancers, the team found that rates were also increasing among people aged 50 or older, in many cases at a similar rate. “This suggests that there are common causes behind these increases,” says Garcia-Closas. The two exceptions were ovarian and bowel cancer.

Next, the team looked at behavioral factors identified by the International Agency for Research on Cancer as being associated with these 11 cancers: alcohol consumption, smoking, physical inactivity, BMI, fiber consumption, and consumption of processed or red meat. “These are the ones that present the strongest evidence for these associations,” says Garcia-Closas.

But researchers found that these risk factors remained largely stable or improved over time. The only one that keeps getting worse is BMI, or excess weight. Although obesity is a risk factor for a number of cancers, the increasing incidence of obesity falls far short of completely explaining the increasing rates of cancer among young people. For example, only about 20 percent of the increase in bowel cancers among young women could be explained by increases in BMI during this period, Garcia-Closas says.

Many studies are trying to determine the causes of these increases, explains Marc Gunter, a member of the team from Imperial College London. “This is a very active area of ​​research at the moment.” Possibilities include higher consumption of ultra-processed foods, “forever chemicals” known as PFAS, and antibiotics that disrupt gut microbiomes.

The researchers’ analysis suggests that the increase in cancers among young people is likely due to a combination of several factors rather than a single cause, and they cannot rule out that changes in diagnosis rates played a role.

This increase also needs to be seen in context, says team member Amy Berrington, also at ICR. For example, in England, only 3,000 cases of bowel cancer are diagnosed each year in people aged 20 to 49, so a 3% increase in cases means around 100 extra cases per year. “These relative trends in a still rare disease mean that the additional number of cases is still quite small,” says Berrington.

The study also left out cervical cancer because cervical cancer rates are plummeting among women who received the HPV vaccine as children.

Finally, Berrinton looked at more recent data on cancer rates, through 2023. “The upward trends have started to flatten out a little bit, so better news is already coming,” she said. Additionally, if rising rates of obesity are partly responsible for higher rates of cancers among young people, then the growing use of GLP-1 weight-loss drugs, such as semaglutide, could help change the trends, Gunter says. “If obesity rates begin to decline with the use of these drugs, this should have an effect on some obesity-related cancers in the future. »