Scientists at the American Cancer Society (ACS) have performed a large study that has indicated that the rates of 17 of 34 types of cancer are rising in younger generations. This includes breast and pancreatic cancers. Mortality rates have also risen for certain cancers: colorectal, gallbladder, testicular, uterine corpus, and female liver cancer. The findings have been reported in The Lancet Public Health.
In this study, investigators analyzed data from two sources: The North American Association of Central Cancer Registries includes 23,654,000 individuals who were diagnosed with 34 types of cancer; and The U.S. National Center for Health Statistics contains cancer mortality data for 7,348,137 deaths for 25 types of cancer. These databases include people who were aged 25 to 84, while the data was collected from January 1, 2000, to December 31, 2019. Cancer rates were compared across groups in five-year periods, by calculating a birth cohort-specific incidence rate ratio and mortality rate ratio for each group, which was also adjusted for age effect and period effect.
Incidence rates were found to increase for eight of 34 cancers in every successive birth cohort that was born since about 1920. The 1990 birth cohort saw the most dramatic increase; incidence rates were two or three times higher for this group compared to the 1955 birth cohort for kidney, pancreatic, and small intestinal cancers in male and female individuals, while liver cancer incidence also rose in female individuals.
After the 1990 cohort, incidence rates continued to increase for younger groups for nine other types of cancer; this includes breast (estrogen-receptor positive only), colorectal, gallbladder, ovarian, and testicular cancers.
"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 corresponding study author Dr. Hyuna Sung, a senior principal scientist 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," added Sung.
"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," noted senior study author Dr. Ahmedin Jemal, senior vice president of surveillance and health equity science at the American Cancer Society.
