Cancer has been declining in older generations, thanks in part to early detection and better treatments. But it’s on the rise in younger generations.
Gen X and millennials are getting 17 types of cancer at higher incidence rates and younger ages than previous generations. Breast, pancreatic and gastric cancers are among those with increasing rates in successively younger generations. And death rates are also rising with some of those cancers, including liver cancer in females, uterine corpus, gallbladder, testicular and colorectal cancers.
That’s according to a study led by the American Cancer Society that is published this week in the journal The Lancet Public Health that says “each successive generation born during the second half of the 20th century has had increased incidences of many common cancer types ... compared with previous generations in the U.S.”
In the study’s introduction, researchers write: “Trends in cancer incidence in young generations or young adults (age <50 years) largely reflect increased exposure to carcinogenic factors during early life or young adulthood compared with previous generations and foreshadow future disease burden as these young cohorts carry their increased risk into older age, when cancers most frequently occur.”
The study doesn’t say what’s causing the increase, but the researchers note that in previous studies, six of the cancers are related to obesity. And they recommend that environmental and lifestyle factors be addressed.
The findings are similar to a June study in JAMA Network Open that used 13 U.S. cancer registries and found that Gen X — those born between 1965 and 1980 — have higher incidence of certain cancers. The list included leukemia, thyroid, colorectal, kidney and uterine corpus.
Counting cancer cases, deaths
The study is based on data from nearly 23.7 million patients who were diagnosed with the 34 types of cancer studied and death records from more than 7.3 million deaths that included 25 different cancer types. The individuals included were between 25 and 84 and the records were from Jan. 1, 2000, to Dec. 31, 2019, taken 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,” the researchers said in an American Cancer Society news release.
For eight of the cancers, incidence rates increased with each new birth cohort, starting in about 1920. For pancreatic, kidney and small intestine cancers in males and females and for liver cancer in females, the incidence was two to three times higher in the 1990 birth group than in the 1955 group.
And although nine of the cancers declined among older birth cohorts, the incidence rates grew in younger groups. Those included breast cancer, uterine corpus cancer, colorectal cancer, non-cardia gastric cancer, gallbladder cancer, ovarian cancer, testicular cancer, and specific to males, anal cancers and Kaposi sarcoma.
The increase for those in the 1990 birth cohort ranged from 12% for ovarian cancer to 169% for uterine corpus cancer compared to the 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,” the release said.
Looking toward prevention
The study’s senior author, Dr. Ahmedin Jemal, cancer society senior vice president, called the increase in cancer rates among younger people a generational shift in cancer risk and said it could “serve as an early indicator of future cancer burden in the country.”
Unless there are effective interventions, he noted, that elevated risk in younger generations will be carried over as people age, wiping out or stopping decades of progress against cancer. “The data highlights the critical need to identify and address underlying risk factors in Gen X and Millennial populations to inform prevention strategies.”