癌症为何越来越年轻化？| 时代周刊

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By Jamie Ducharme

Researchers have found that young people around the world are getting many different kinds of cancer at alarmingly high rates. And as the diagnoses of celebrities and public figures like Kate Middleton, Chadwick Boseman, Dwyane Wade, and Olivia Munn bring mass attention to the issue, scientists are racing to answer a question on the minds of many outside the medical profession: Why is cancer, historically a disease of old age, increasingly striking people in the primes of their lives?

Globally, diagnoses and deaths related to early-onset cancers—those 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. In the U.S., breast cancer is the most common type of early-onset disease, but recent surges in cancers affecting digestive organs—including the colon, rectum, pancreas, and stomach—are particularly dramatic within this age group. In fact, today’s young adults are about twice as likely to be diagnosed with colon cancer—and four times as likely to be diagnosed with rectal cancer—as those born around 1950, research suggests.

Overall, cancer is still overwhelmingly an older person’s disease. As of 2025, 88% of people in the U.S. diagnosed with cancer were 50 or older, and 59% were 65 or older, according to data from the American Cancer Society. But there is no question that the demographics are shifting. Under 50s are not only at increasing risk of suffering from cancer; theirs is the only age group for which the risk is rising. All told, 17 types of cancer are on the rise among U.S. adults in this age group.

“When we were younger, we assumed the climate would be the same forever. The same applies in cancer,” says Dr. Thomas Powles, a U.K.-based oncologist and cancer researcher who edits the journal Annals of Oncology. “We just assumed that cancer incidence was something that is relatively static. But it’s not.”

There is some good news in the data. Advances in disease detection and treatment, as well as dramatic declines in smoking, mean that far fewer people die from cancer now than once did. Although the disease still ranks as the second most common cause of death in the U.S., killing more than half a million people each year, mortality rates have dropped by about a third since 1991.

Less encouragingly, the rate of new cancers diagnosed has remained stubbornly consistent, declining only modestly from 1999 to 2021. Across the U.S., roughly 2 million new cancer cases are detected each year, diagnoses that, on top of the emotional toll, force patients to cumulatively fork out billions of dollars in out-of-pocket costs—more than $16 billion in 2019 alone, according to federal data. Today, about 40 out of every 100 U.S. adults can expect to be diagnosed with cancer at some point in their lifetimes. For an estimated 1 in 17 U.S. women and 1 in 29 U.S. men, that news will come before their 50th birthdays.

The rise in early-onset diagnoses partly comes down to advances in our ability to detect and diagnose different kinds of cancers. “With much more sophisticated tools now, inevitably we’re doing more tests on younger people [and] we’re using more accurate imaging,” which leads to more cancers detected, Powles says. Some screening protocols have also been modified in recent years to include younger adults; since 2018, for example, the American Cancer Society has recommended colonoscopies starting at age 45, down from 50.

But this is only one part of what scientists say is a more complex web of factors they are still attempting to understand. The data suggest that some element—or perhaps combination of elements—of modern life is sickening progressively younger adults. And right now, no one knows for sure what that is.

There are plenty of known risk factors for cancer, from the genes someone is born with to the unhealthy lifestyle habits they pick up, such as smoking, drinking lots of alcohol, or spending time in the sun. Such habits can speed up the natural degradation of cells, which over time acquire genetic mutations as they lose their ability to repair damage. As that damage accumulates with age, cells may become cancerous, growing and -multiplying too fast for the body’s immune system to keep them in check and potentially choking out vital organs. The immune system also loses some of its strength with age, making it easier for cancer cells to colonize the body.

But classic risk factors do not seem to fully explain the recent rise in early-onset cancers, says Dr. Cathy Eng, director of the Young Adult Cancers Program at Vanderbilt University’s Ingram Cancer Center in Tennessee. Some of the trends are baffling; young, nonsmoking women, for example, are being diagnosed with lung cancer in strangely high numbers. Many times, Eng’s patients were extremely healthy: vegetarians, marathon runners, avid swimmers. “That’s why I really believe there’s other risk factors to account for this,” she says.

There’s no shortage of theories about what those may be. Many scientists point to modern diets, which tend to be heavy on potentially carcinogenic products—including ultra-processed foods, red meat, and alcohol—and may also contribute to weight gain, another cancer risk factor. The foods we eat can also affect the gut microbiome, the colony of microbes that lives in the digestive system and appears linked to overall health. Alterations to the gut microbiome via diet, or perhaps exposure to drugs like antibiotics, have also been implicated.

Other researchers blame the microplastics littering our environment and leaching into our food and water supplies, some of which, according to a 2024 study, have even shown up in cancer patients’ tumors. Other environmental factors could also be to blame, given that everything from cosmetics to food packaging contains substances that many researchers aren’t convinced are safe. Even our near constant exposure to artificial light could be messing with normal biological rhythms in ways that have profound health consequences, some research suggests.

For now, these are all just hypotheses. Some may turn out to be wrong, and more theories will emerge in time. It’s also likely that different risk factors are linked to different cancers, Frizelle says. Even in a single patient, multiple overlapping triggers may be in play. ■

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