Although cancer most commonly occurs among older adults, rates of early-onset cancer among people under 50 have been on the rise over the last few years — an unexpected development that health experts say "none of us really know the answer to," Felice Freyer reports in STAT+.
Although cancer is around 20 times more common among older individuals than younger ones, doctors have reported a growing trend of new cancer diagnoses among those under 50 — something they used to only see infrequently.
For example, rates of colorectal cancer among people under 50 have increased by around 2% a year since the 1990s. This increase has been observed "in both men and women and in all races and ethnicities and around the world," said Kimmie Ng, director of the Young-Onset Colorectal Cancer Center at the Dana-Farber Cancer Institute.
Similarly, breast cancer rates among women under 50 have begun to increase in recent years. Although there was only a slight increase in rates between 2000 and 2015, they increased by 2% a year between 2015 and 2019.
Pancreatic cancer, which only has a 10% survival rate, is also increasing among younger individuals. According to data from the National Cancer Institute, pancreatic cancer rates have increased by 6.5% a year from 2017 and 2019 for men under 50. Among women, pancreatic cancer rates increased by 2.4% between 2000 and 2019.
Many other cancers are also on the rise. In an analysis of data from 44 countries, researchers found that rates of over a dozen cancers have increased among people under 50. Aside from colorectal, breast, and pancreatic cancer, the other types of cancer that are increasing include uterine, kidney, thyroid among women and kidney, liver, prostate, and thyroid among men.
According to Timothy Rebbeck, a professor of cancer prevention at the Harvard T.H. Chan School of Public Health, why early-onset cancers are becoming more common is a "very hard question that none of us really know the answer to."
However, many health experts theorize that lifestyle changes over the last 50 years may have played a role in these growing rates.
"People born in 1990 have over double the risk of getting colon cancer compared to those born in 1950. And quadruple the risk of getting rectal cancer," Ng said.
Some of the lifestyle changes over the last 50 years include less physical activity, eating more cured meats and sugar-sweetened drinks, taking antibiotics, and more. "[T]hese practices — their effects probably interacting — seem to have had a profound impact on the internal workings of our bodies, disrupting metabolism and boosting inflammation," Freyer writes.
In addition, while genetic risks of cancer haven't changed, genes may impact how a person is affected by certain risk factors for cancer, such as obesity, lack of exercise, poor diet, and more.
"The hypothesis is that there are susceptible people out there who are now being exposed to more risk factors or exposed to those risk factors earlier," Rebbeck said.
However, even patients who are relatively healthy are being diagnosed with cancer at higher rates than before.
"[A]necdotally, I can just tell you that so many of my young patients that we see are perfectly fit," Ng said. "They're marathon runners, they have healthy diets, they are not obese. And so it does go beyond just obesity."
There is also some evidence that may suggest that early-onset cancers are biologically different than cancers that occur later in life.
For example, Andrew Chan, a gastroenterologist and chief of the clinical and translational epidemiology unit at Massachusetts General Hospital, said his young adult patients who undergo colonoscopies for gastrointestinal issues often already have polyps, which are a precursor to colon cancer.
"We're finding polyps at 25 or 30 years old," Chan said. "It's clear that there is something different happening even before someone turns 25." Colon cancer tumors also tend to form on the left side of the colon and in the rectum in young people, while there is no such pattern among older adults.
As rates of early-onset cancer increase, more research is being done to understand its potential causes to help reduce the risks for patients in the future.
At Dana-Farber Cancer Institute, the Beyond CRC Project is currently enrolling patients with early-onset colon cancer in a study that will gather detailed data on their lifestyle and diet, analyze their tumors, and collect blood and stool samples.
"We do think that it may be other changes in the environment" that may be leading to higher cancer rates among younger people, Ng said. "Is it increasing antibiotic use? Is it components of these ultra processed foods that have emerged with modern lifestyles, that is changing the microbiome?"
The National Cancer Institute and Cancer Research UK have also listed early-onset cancer as a "grand challenge" for researchers, and the winning team will receive $25 million next year.
"It is encouraging that so much attention is being paid to the early-onset cancer issue," Rebbeck said. "There is scientific progress being made, and I hope we will have answers." (Freyer, STAT+ [subscription required], 7/24)
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