As cancer cases rise among young adults in the United States, a new study has identified 17 types of cancer that appear to be more common in Generation X and millennials than in older age groups.
Among adults born between 1920 and 1990, there is a significant difference between each generation in the incidence of cancer rates and types of cancer, including cancers of the breast, colon and rectum, pancreas and uterus, according to the study published Wednesday in the journal The Lancet Public Health.
“Uterine cancer is one that really stands out and where we see tremendous increases. It has about a 169% higher incidence rate if you’re born in the 1990s compared to if you’re born in the 1950s, and this is for people of the same age. Someone born in the 1950s, when they were in their 30s or 40s, had a different incidence rate compared to someone born in the 1990s, when they were in their 30s or 40s,” said Dr. William Dahut, chief scientific officer of the American Cancer Society, whose colleagues co-authored the new study.
“What’s a little different about this paper is that it includes a broader range of cancers,” he said. “We actually looked at 34 different cancers, where we saw an increase in incidence for 17 and an increase in mortality for five in young adults under 50.”
These 17 types of cancer are:
- breast with estrogen receptor positive
- liver and intrahepatic bile duct in women
- Non-HPV-associated oral and pharyngeal cancers in women
- gallbladder and other biliary tract
- gastric not associated with the cardia
- Kaposi’s sarcoma, which affects the tissue of blood and lymph vessels, in men
The researchers, from the American Cancer Society and the University of Calgary in Canada, analyzed data on more than 23 million patients diagnosed with 34 types of cancer and more than 7 million people who died from 25 types of cancer.
The data, which came from the North American Association of Central Cancer Registries and the National Center for Health Statistics, included adults aged 25 to 84 years from January 2000 to December 2019. The researchers calculated cancer incidence rates and cancer death rates by year of birth, separated by five-year intervals, from 1920 to 1990.
The researchers found that incidence rates increased with each successive cohort born since about 1920 for eight of the 34 cancer types. The rate was about two to three times higher among those born in 1990 than among those born in 1955 for cancers of the pancreas, kidney and small intestine in both men and women and for liver cancer in women.
Across all cancer types, the highest incidence rates among those born in 1990 ranged from 12% higher for ovarian cancer to 169% higher for uterine corpus cancer compared with cohorts with the lowest incidence rates.
The rising incidence of certain cancers among young adults nationwide suggests that “this increase is potentially due to changes in environment or lifestyle,” Dr. Andrea Cercek, a gastrointestinal oncologist and co-director of the Center for Early-Onset Gastrointestinal and Colorectal Cancers en Memorial Sloan Kettering Cancer Center.
“What this study shows is that some cancers that were previously uncommon among young adults are now increasing in incidence,” said Cercek, who was not involved in the new research. “It’s not known why these cancers, such as gastrointestinal cancers, gynecologic cancers and estrogen receptor-positive breast cancers, are increasing in incidence among young adults, but we believe this increase is likely due to early exposure to one or more environmental factors.”
The researchers found that 10 of the 17 cancers with an increasing incidence in younger birth cohorts are related to obesity: colon and rectum, kidney and renal pelvis, gallbladder and other biliary tract, uterine corpus, pancreas, gastric cardia, estrogen receptor-positive breast, ovary, myeloma, and liver and bile duct.
Because cancer takes time to develop, obesity-related cancer in a young adult could be associated with their childhood health.
“If people develop cancer at a younger age, that means their exposure, whether it was environmental, climatic, dietary or whatever, also occurred at a younger age,” Dahut said. “If you get cancer in your 30s or 20s, then your teenage years, or even earlier, is probably the time when you had that exposure or triggering event.”
The researchers also found that cancer death rates increased in successively younger generations along with incidence rates of liver cancer among women, cancer of the uterine corpus, gallbladder, testes, colon and rectum.
The new study had good news: Cancers that are not increasing, and are even declining in younger generations, include those related to tobacco, such as lung cancer, and HPV infections, such as cervical cancer.
The “accelerated decline” in cervical cancer incidence trends shows the effectiveness of HPV vaccination among women born around 1990, who were about 16 years old when the vaccine was approved in the United States, the study found. And the declining trends in tobacco-related cancers parallel a rapid decline in smoking prevalence among younger generations.
“These findings add to growing evidence of increased cancer risk in generations after the Baby Boomer generation, and extend previous findings on early-onset colorectal cancer and some obesity-associated cancers to encompass a broader range of cancer types,” the study said in a news release. Dr. Hyuna Sunglead author of the study and senior scientist for surveillance and health equity at the American Cancer Society.
“Birth cohorts — groups of people categorized by their birth year — share unique social, economic, political and climatic environments, which affect their exposure to cancer risk factors during their crucial developmental years,” she said. “Although we have identified cancer trends associated with birth years, we still do not have a clear explanation for why these rates are increasing.”
A growing trend towards early detection
Several factors, including dietary changes, declining levels of physical activity, rising rates of childhood obesity and increased use of more advanced diagnostic tests, are likely behind the rising incidence of cancer among younger age groups, said Dr. Ernest Hawk, president of the Division of Cancer Prevention and Population Sciences at the University of Texas MD Anderson Cancer Center, who was not involved in the study.
“In particular, because we know that several of these cancers are linked to obesity, they may be the most likely of the possible culprits that have been discussed so far,” Hawk said.
However, health care professionals in the United States have the tools to diagnose many of these cancers at early stages, leading to better survival odds, Hawk added, and the new findings indicate that we may need to start screening at younger ages for some cancers.
“That’s already happened with both breast cancer screening and colon cancer screening. For both, just in the last five years, we’ve lowered the age at which screening starts in the average-risk general population,” Hawk said. “So the downward migration in the age at which screening starts has already started to move in that direction for some cancers, in part for this very reason.”
Hawk was referring to screening guidelines from the U.S. Preventive Services Task Force (USPSTF), a voluntary panel of independent medical experts whose recommendations help guide doctors’ decisions and influence insurance plans.
In 2021, the USPSTF The U.S. Department of Health lowered the recommended age for starting colorectal cancer screening to average-risk adults ages 50 to 45. This guidance is for those who are asymptomatic and do not have a diagnosis of colorectal cancer, a history of colon or rectal polyps, or a personal or family history of genetic disorders that put them at higher risk.
In May, the task force updated its breast cancer screening recommendations for average-risk adults, advising a mammogram every two years starting at age 40 and continuing through age 74. The previous recommendation called for biennial mammograms to begin at age 50 and that the decision for women to be screened at age 40 “should be an individual one.” The new guidelines align more closely with those of other groups, such as the American Cancer Society.
Overall, “the findings of increased cancer incidence in recent birth cohorts for 17 cancer types have important public health implications,” the researchers wrote in their study. “Improving awareness among health care providers and the general public about the signs and symptoms of cancer among young adults is crucial for early detection and treatment.”
Dahut said signs and symptoms of most types of cancer can include abnormal bleeding, as blood in the stool can be a sign of colorectal cancer or unusual vaginal bleeding can be a symptom of uterine cancer.
Other symptoms to look out for include “sharp, persistent pain that you’ve never had before — that’s something else that people should at least get medical advice for,” Dahut said.
“Any abnormal lymph nodes or unexplained growths,” she added. “Fatigue and weight loss tend to be in much more advanced cancers, and I think at that point, most people are usually seeing someone because they’re feeling unwell.”
Dahut said seeking medical care remains important as “delaying diagnosis six, eight, 10 or 12 months before going can definitely lead to more advanced disease and a worse prognosis.”
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