A new large study led by researchers
at the American Cancer Society (ACS) suggests incidence rates
continued to rise in successively younger generations in 17 of the
34 cancer types, including breast, pancreatic, and gastric cancers.
Mortality trends also increased in conjunction with the incidence of
liver (female only), uterine corpus, gallbladder, testicular, and
colorectal cancers. The report will be published today in the
journal
The Lancet Public Health.
“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.”
In this analysis, researchers obtained incidence data from
23,654,000 patients diagnosed with 34 types of cancer and mortality
data from 7,348,137 deaths 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
U.S. National Center for Health Statistics, respectively. To compare
cancer rates across generations, they calculated birth
cohort-specific incidence rate ratios and mortality rate ratios,
adjusted for age effect and period effect, by birth years, separated
by five-year intervals, from 1920 to 1990.
Researchers found that incidence rates increased with each
successive birth cohort born since approximately 1920 for eight of
34 cancers. In particular, the incidence rate was approximately
two-to-three times higher in the 1990 birth cohort than in the 1955
birth cohort for pancreatic, Kidney, and small intestinal cancers in
both male and female individuals; and for liver cancer in female
individuals. Additionally, incidence rates increased in younger
cohorts, after a decline in older birth cohorts, for nine of the
remaining cancers including breast cancer (estrogen-receptor
positive only), uterine corpus cancer, colorectal cancer, non-cardia
gastric cancer, gallbladder 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% for ovarian cancer to 169% for uterine
corpus cancer higher than the rate in the birth cohort with the
lowest incidence rate. Notably, mortality rates increased in
successively younger birth cohorts alongside incidence rates for
liver cancer (female only), uterine corpus, gallbladder, testicular,
and colorectal cancers.
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“The increase in cancer rates among this younger group of people
indicate generational shifts in cancer risk and often serve as an
early indicator of future cancer burden in the country. Without
effective population-level interventions, and as the elevated risk
in younger generations is carried over as individuals age, an
overall increase in cancer burden could occur in the future, halting
or reversing decades of progress against the disease,” added Dr.
Ahmedin Jemal, senior vice president, surveillance and health equity
science at the American Cancer Society and senior author of the
study. “The data highlights the critical need to identify and
address underlying risk factors in Gen X and Millennial populations
to inform prevention strategies.”
"The increasing cancer burden among younger generations underscores
the importance of ensuring people of all ages have access to
affordable, comprehensive health insurance, a key factor in cancer
outcomes," said Lisa Lacasse, president of the American Cancer
Society Cancer Action Network (ACS CAN). "To that end, ACS CAN will
continue our longstanding work to urge lawmakers to expand Medicaid
in states that have yet to do so as well as continue to advocate for
making permanent the enhanced Affordable Care Act tax subsidies that
have opened the door to access to care for millions."
Other ACS researchers participating in the study include: Chenxi
Jiang, Dr. Priti Bandi, Dr. Farhad Islami, and Rebecca Siegel.
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