Young adults in the U.S. demonstrated a higher risk for obesity-related cancers than previous generations, according to a study recently published in Lancet Public Health.
This risk increased in progressively younger age groups, with millennials exhibiting nearly double the risk for certain malignancies than baby boomers had at the same age.
“Although the absolute risk of these cancers is small in younger adults, these findings have important public health implications,” study author Ahmedin Jemal, PhD, scientific vice president of surveillance and health services research at American Cancer Society, said in a press release. “Given the large increase in the prevalence of overweight and obesity among young people and increasing risks [for] obesity-related cancers in contemporary birth cohorts, the future burden of these cancers could worsen as younger cohorts age, potentially halting or reversing the progress achieved in reducing cancer mortality over the past several decades.”
The study extends a prior analysis that showed increases in early-onset colorectal cancer in the U.S., a trend seen in other high-income countries that may be indicative of the obesity epidemic of the past 40 years.
The International Agency for Research on Cancer also identified the following malignancies as potentially obesity-related: esophageal, gallbladder, gastric cardia, kidney, liver and intrahepatic bile duct, pancreatic, thyroid, uterine corpus, breast and ovarian cancers, and multiple myeloma.
In the current study, Jemal and colleagues reviewed 25 state registries covering 67% of the U.S. population to identify incidence of invasive cancers among people aged 25 to 84 years. The study included patients diagnosed between 1995 and 2014. Researchers evaluated 14,672,409 incident cases for 30 types of cancer, including 18 of the most common types and the 12 obesity-related cancers.
They estimated average annual percentage change in incidence rates by 5-year age group (25-29 years to 80-84 years) by applying an age-period-cohort model to each cancer type. They calculated incidence rate ratios by birth cohort (10-year overlapping birth cohorts from 1910-19 to 1980-89 in 5-year increments).
Results showed significant, increases in six of the 12 obesity-related cancers — multiple myeloma, and colorectal, uterine corpus, gallbladder, kidney and pancreatic cancers — among adults aged 25 to 49 years over the 20-year period, with more pronounced increases in each consecutive younger generation.
The risk for colorectal, uterine corpus, pancreas and gallbladder cancers among millennials was about double the rate observed among baby boomers at the same age.
Among adults aged 25 to 29 years, researchers observed annual increases ranging from 1.44% (95% CI, 0.6-3.53) for multiple myeloma to 6.23% (95% CI, 5.32-7.14) for kidney cancer. Adults aged 45 to 49 years demonstrated annual increases of 0.37% (95% CI, 0.03-0.72) for uterine corpus cancer to 2.95% (95% CI, 2.74-3.16) for kidney cancer.
Adults aged 50 years and older also showed increases in age-specific incidence of several obesity-related cancers — including gallbladder, kidney, pancreas and thyroid cancers, and multiple myeloma — but to a lesser extent than younger adults, except for thyroid cancer.
Incidence rate ratios for individuals born around 1985 compared with those in the reference birth cohort (born around 1950) ranged from 1.59 (95% CI, 1.14-2.21) for multiple myeloma to 4.91 (95% CI, 4.27-5.65) for kidney cancer.
Rates of only two nonobesity-related cancers — gastric non-cardia cancer and leukemia — increased among each successive generation of young adults. Eight of the other cancers, including those associated with smoking and HIV infection, decreased in successive generations of young adults.
The researchers noted several limitations to their study, including the conjecture associated with age-period-cohort modeling and the lack of sufficient data to establish a causal relationship between the obesity epidemic and early-onset cancer.
According to the researchers, additional studies are needed to identify factors that may be driving these trends, and to develop strategies to address this problem.
Jemal said these findings may have value in terms of predicting the future trajectory of these cancers.
“Cancer trends in young adults often serve as a sentinel for the future disease burden in older adults, in whom most cancer occurs,” he said. – by Jennifer Byrne
Disclosures: The researchers report no relevant disclosures.