US and Canadian researchers have identified 17 cancer types that appear to be more common in Generation X and millennials than in older age groups, after analysing data from more than 23m patients – but on the upside, found that lung cancer and cervical cancer rates are dropping.
Among adults born between 1920 and 1990, they found 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 in The Lancet Public Health.
“Uterine cancer is one that really jumps out – 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,” said Dr William Dahut, chief scientific officer for the American Cancer Society, whose colleagues authored the study.
“Someone born in the 1950s… when they were in their 30s or 40s… saw a different incidence rate compared with those born in the 1990s when they got to their 30s or 40s,” he added.
“What’s different about this paper is that it includes a wider variety of cancers. It actually looked at 34 different cancers, in 17 of which we saw an increase in incidence, and five an increase in mortality in young adults under 50.”
Those 17 cancers are:
gastric cardia
small intestine
oestrogen 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
leukaemia
Kaposi sarcoma, which affects the lining of blood vessels and lymph vessels, in men.
CNN reports that the researchers, from the American Cancer Society and the University of Calgary in Canada, analysed data on more than 23m patients diagnosed with 34 types of cancer and more than 7m 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 Centre for Health Statistics, included adults between 25 and 84, from January 2000 to December 2019.
The researchers calculated cancer incidence rates and cancer death rates by birth years, separated by five-year intervals, from 1920 to 1990, and found that the incidence rates had 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 suggests the rise is potentially due to changes in the environment or lifestyle,” said Dr Andrea Cercek, a gastrointestinal medical oncologist and co-director of the Centre for Young Onset Colorectal and Gastrointestinal Cancers at Memorial Sloan Kettering Cancer Centre.
“The study shows that some cancers which were previously not prevalent in young adults, are now rising,” added Cercek, who was not involved with the study.
“It is not known why gastrointestinal, gynaecological and ER-positive breast cancers are rising in young adults, but we believe it may be 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, oestrogen 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 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,” said Dr Hyuna Sung, lead author of the study and a senior principal scientist of surveillance and health equity science at the American Cancer Society.
“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.
“Although we have identified cancer trends associated with birth years, we don’t yet have a clear explanation for why these rates are rising.”
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 Centre, who was not involved in the study.
He added that the findings signal that screening might need to start 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 past 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.”
“Overall, the findings of increased cancer incidence in recent birth cohorts for 17 cancer types have important public health implications,” the researchers wrote.
“Improving awareness among healthcare providers and the public about the signs and symptoms of cancer among young adults is crucial for early detection and treatment.”
Study details
Differences in cancer rates among adults born between 1920 and 1990 in the USA: an analysis of population-based cancer registry data
Hyuna Sung, Chenxi Jiang, Priti Bandi, et al.
Published in The Lancet Public Health in August 2024
Summary
Background
Trends in cancer incidence in recent birth cohorts largely reflect changes in exposures during early life and foreshadow the future disease burden. Herein, we examined cancer incidence and mortality trends, by birth cohort, for 34 types of cancer in the USA.
Methods
In this analysis, we obtained incidence data for 34 types of cancer and mortality data for 25 types of cancer for individuals aged 25–84 years for the period Jan 1, 2000, to Dec 31, 2019 from the North American Association of Central Cancer Registries and the US National Centre for Health Statistics, respectively. We calculated birth cohort-specific incidence rate ratios (IRRs) and mortality rate ratios (MRRs), adjusted for age and period effects, by nominal birth cohort, separated by 5 year intervals, from 1920 to 1990.
Findings
We extracted data for 23 654 000 patients diagnosed with 34 types of cancer and 7 348 137 deaths from 25 cancers for the period Jan 1, 2000, to Dec 31, 2019. We found that IRRs increased with each successive birth cohort born since approximately 1920 for eight of 34 cancers (pcohort<0·050). Notably, the incidence rate was approximately two-to-three times higher in the 1990 birth cohort than in the 1955 birth cohort for small intestine (IRR 3·56 [95% CI 2·96–4·27]), kidney and renal pelvis (2·92 [2·50–3·42]), and pancreatic (2·61 [2·22–3·07]) cancers in both male and female individuals; and for liver and intrahepatic bile duct cancer in female individuals (2·05 [1·23–3·44]). Additionally, the IRRs increased in younger cohorts, after a decline in older birth cohorts, for nine of the remaining cancers (pcohort<0·050): oestrogen-receptor-positive breast cancer, uterine corpus cancer, colorectal cancer, non-cardia gastric cancer, gallbladder and other biliary cancer, ovarian cancer, testicular cancer, anal cancer in male individuals, and Kaposi sarcoma in male individuals. Across cancer types, the incidence rate in the 1990 birth cohort ranged from 12% (IRR1990 vs 1975 1·12 [95% CI 1·03–1·21] for ovarian cancer) to 169% (IRR1990 vs 1930 2·69 [2·34–3·08] for uterine corpus cancer) higher than the rate in the birth cohort with the lowest incidence rate. The MRRs increased in successively younger birth cohorts alongside IRRs for liver and intrahepatic bile duct cancer in female individuals, uterine corpus, gallbladder and other biliary, testicular, and colorectal cancers, while MRRs declined or stabilised in younger birth cohorts for most cancers types.
Interpretation
A total of 17 of 34 cancers had an increasing incidence in younger birth cohorts, including nine that previously had declining incidence in older birth cohorts. These findings add to growing evidence of increased cancer risk in younger generations, highlighting the need to identify and tackle underlying risk factors.
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Cancer diagnoses among younger people rising
Steep climb in under-50 cancer cases, global study finds
Vital early signs of colon cancer in young adults – US study
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