(CNN) — As cancer cases rise among young adults in the United States, a new study has identified 17 cancer types that appear to be more common in Generation X and millennials than 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 cancer types, including breast, colon and rectal, pancreatic and uterine cancers, according to the study published Wednesday in the journal The Lancet Public Health.
“Uterine cancer is one that really jumps out where we see tremendous increases. It has about a 169% higher incidence rate if you’re born in the 1990s as opposed to if you’re born in the 1950s – and this is for people at the same age. Someone born in the 1950s, when they were in their 30s or 40s, saw a different incidence rate compared with someone born in the 1990s in their 30s or 40s,” said Dr. William Dahut, chief scientific officer for the American Cancer Society, whose colleagues authored the new study.
“What’s a little different about this paper is that it includes a wider variety of cancers,” he said. “It actually looked at 34 different cancers in which 17, we saw an increase in incidence, and five an increase in mortality in young adults under the age of 50.”
Those 17 cancers are:
- gastric cardia
- small intestine
- estrogen receptor-positive breast
- ovary
- liver and intrahepatic bile duct in women
- non-HPV-associated oral and pharynx cancers in women
- anus
- colon and rectal
- uterine corpus
- gallbladder and other biliary
- kidney and renal pelvis
- pancreas
- myeloma
- non-cardia gastric
- testis
- leukemia
- Kaposi sarcoma, which affects the lining of blood vessels 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 of 25 types of cancer.
The data, which came from the North American Association of Central Cancer Registries and the US National Center for Health Statistics, included adults ages 25 to 84 from January 2000 through December 2019. The researchers calculated cancer incidence rates and cancer death rates by birth years, separated by five-year intervals, from 1920 to 1990.
The researchers found that the incidence rates increased with each successive cohort born since about 1920 for eight of 34 cancers. The rate was about two to three times higher among those born in 1990 than among those born in 1955 for pancreatic, kidney and small intestinal cancers in both men and women and for liver cancer in women.
Across cancer types, the increased incidence rate among people born in 1990 ranged from 12% higher for ovarian cancer to 169% higher for uterine corpus cancer compared with the birth cohorts that had the lowest incidence rates.
The increasing incidence of certain cancers among young adults nationally suggests that “this rise is potentially due to changes in the environment or lifestyle,” Dr. Andrea Cercek, a gastrointestinal medical oncologist and co-director of the Center for Young Onset Colorectal and Gastrointestinal Cancers at Memorial Sloan Kettering Cancer Center, said in an email.
“What this study shows is that some cancers which were previously not prevalent in young adults, are now rising in incidence,” said Cercek, who was not involved with the new research. “It is not known why these cancers, such as gastrointestinal cancers, gynecologic cancers, and ER-positive breast cancers, are rising in incidence in young adults, but we believe this rise is likely due to early exposure to an environmental factor or factors.”
The researchers found that 10 of the 17 cancers with increasing incidence in younger birth cohorts are related to obesity: colon and rectal, kidney and renal pelvis, gallbladder and other biliary, uterine corpus, pancreas, cardia gastric, estrogen receptor-positive breast, ovary, myeloma, and liver and bile duct.
As cancer requires time to develop, an obesity-related cancer in a young adult could be associated with their childhood health.
“If people are developing cancer at an earlier age, that means that their exposure – whether it was environmental or climate or diet or whatever else – occurred at a younger age too,” Dahut said. “If you have cancer in your 30s or 20s, then your teens, or even earlier, is probably the time when you had that exposure or the instigating event.”
The researchers also found that cancer death rates increased in successively younger generations alongside incidence rates for liver cancer among women, uterine corpus, gallbladder, testicular, and colon and rectal cancers.
The new study had some good news: The cancers that are not rising – and are even on the decline in younger generations – include those related to tobacco, such as lung cancer, and HPV infections, such as cervical cancer.
The “accelerated downturn” in the trend of cervical cancer incidence shows the effectiveness of HPV vaccination among women born around 1990, who were about 16 years old when that vaccination was approved in the United States, according to the study. And the downward trends for tobacco-related cancers parallel a rapid decline in the prevalence of smoking among younger generations.
“These findings add to growing evidence of increased cancer risk in post-Baby Boomer generations, expanding on previous findings of early-onset colorectal cancer and a few obesity-associated cancers to encompass a broader range of cancer types,” Dr. Hyuna Sung, lead author of the study and a senior principal scientist of surveillance and health equity science at the American Cancer Society, said in a news release.
“Birth cohorts, groups of people classified by their birth year, share unique social, economic, political, and climate 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 don’t yet have a clear explanation for why these rates are rising.”
A growing trend of earlier screening
Several factors – including changes in diet, decreased physical activity levels, rising childhood obesity rates and the increased use of more advanced diagnostic tests – are probably behind the rising cancer incidence among younger age groups, said Dr. Ernest Hawk, chair 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.
“Particularly because several of these cancers we know to be obesity-related cancers, that may be the most likely of the possible culprits that have been discussed thus far,” Hawk said.
However, health care practitioners in the United States have the tools to diagnose many of these cancer types at early stages, leading to higher chances of survival, Hawk added, and the new findings signal that we may need to start screening at earlier ages for some types of cancer.
“That has already taken place for both breast cancer screening as well as colon cancer screening. For both of those, just within the last five years, we have decreased the age at which to initiate screening in the general, average-risk population,” Hawk said. “So the downward migration in the age to start screening has already begun to move in that direction for some cancers, partly for this very reason.”
He was referring to screening guidelines from the US Preventive Services Task Force, a volunteer panel of independent medical experts whose recommendations help guide doctors’ decisions and influence insurance plans.
In 2021, the USPSTF lowered the recommended age to start screening average-risk adults for colon and rectal cancers from 50 to 45. This guidance is for those who do not have symptoms and who have no diagnosis of colorectal cancer, history of colon or rectal polyps, or 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 other year starting at age 40 and until age 74. The previous recommendation called for biennial mammograms to start by age 50 and that the decision for women to screen in their 40s “should be an individual one.” The new guidelines more closely align 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 that signs and symptoms of most cancer types may include abnormal bleeding, since 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 be aware of include “dull, 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 growths that are unexplained,” he added. “Fatigue, weight loss – those tend to be with much more advanced cancer, and I think at that point, most people tend to see somebody because they feel sick.”
Seeking medical attention remains important since, Dahut said, “delaying a diagnosis by six, eight, 10 or 12 months before you go in can definitely lead to more advanced disease and a worse outcome.”
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