A new international study is challenging the idea that cancer is rising mainly in young adults.
Researchers found that cancer rates are climbing across nearly all adult age groups, and obesity is playing a major role in the surge.
The study analyzed cancer registries from 42 countries across five continents between 2003 and 2017. The findings were published in Annals of Internal Medicine.
Six cancers rose in adults ages 20 to 49 in most of the countries studied. These included thyroid, breast, kidney, endometrial, leukemia, and colorectal cancer. Five of the six also increased among adults 50 and older. The only exception was colorectal cancer, which rose much faster in younger adults.
Five of the cancers that increased in both age groups have established links to obesity. Endometrial and kidney cancer showed some of the strongest connections and recorded median annual increases above 1.6 percent in younger adults. Researchers say rising obesity rates now affect multiple generations and are likely driving cancer risk in both younger and older adults.
The pattern is not universal. Stomach and esophageal cancer, which also have obesity associations, actually declined among younger adults in more than half the countries studied. Obesity alone does not explain every trend.
Thyroid cancer showed the largest annual increase in younger adults, rising by a median of 3.57 percent per year. Kidney cancer increased at 2.21 percent and endometrial cancer at 1.66 percent. Breast cancer rose at 0.89 percent annually, even though obesity is linked to lower breast cancer risk in premenopausal women.
Colorectal cancer stood out. Rates increased in younger adults in 88 percent of countries but only rose in older adults in about half. Researchers believe screening plays an important role. Colonoscopies catch cancer early and prevent many cases by removing precancerous polyps, which protects older adults who are regularly screened.
Several cancers are declining. Stomach cancer dropped in younger adults in 77 percent of countries. Esophageal and oral cancer also declined in many countries. Among older adults, liver and oral cancer increased in more than half of nations, while stomach and esophageal cancer decreased.
Regional patterns varied. Prostate cancer increased in younger adults in 80 percent of European countries but only 40 percent of those in the Americas. Thyroid and kidney cancer rose across most countries in Asia, Europe, and the Americas. In nine countries, thyroid cancer rates recently began falling among younger adults, but the overall 15-year trend remains upward.
Despite rising rates in younger adults, older adults still account for most cancer cases worldwide. In 2020, people 50 and older made up more than two-thirds of new cancer diagnoses and 71 percent of cancer deaths.
In the United States in 2022, about 50,000 breast cancer cases were diagnosed in women younger than 50, compared to 210,000 in those 50 and older. Prostate cancer totaled 4,000 cases in men under 50, compared to 220,000 in older men.
Scientists say more research is needed into the “global exposome,” meaning the full range of environmental and behavioral factors shaping cancer risk. Diet, physical activity, antibiotic use, air pollution, and microbiome changes may contribute.
The projected financial toll of global cancer treatment is expected to exceed 25 trillion dollars over the next 30 years. Many countries already face shortages of oncology providers and limited clinical trial data for both younger and older patients.
Researchers say the findings do not support treating early onset cancer as a separate crisis. Instead, cancer is rising in adults of all ages, and addressing global risk factors such as obesity will be important for long-term prevention.