Generation X and Millennials in the United States, brace yourselves for some startling news from researchers: your generations have a higher risk of developing cancer compared to older ones.

In a study led by the American Cancer Society, a research team analyzed birth cohorts in five-year intervals from 1920 to 1990 to estimate the incidence rates of 34 different types of cancer. The results published in the journal Lancet Public Health revealed a troubling trend: 17 types of cancers, including breast, pancreatic, and gastric cancers, are rising in successively younger generations. The mortality rates for cancers along with the incidence of cancers such as liver in females, uterine corpus, gallbladder, testicular, and colorectal also continue to rise.

"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," Dr. Hyuna Sung, lead author of the study, said in a news release.

The findings were made after examining 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 between Jan. 1, 2000, and Dec. 31, 2019. To compare cancer rates across generations, researchers calculated incidence rate and mortality rate ratios for each birth cohort, adjusting for age and period, in five-year intervals from 1920 to 1990. A birth cohort is a group of people classified by their birth years.

For eight out of 34 cancers studied, the incidence rate increased with each successive birth cohort born since approximately 1920. The study noted that the 1990 birth cohort has approximately two to three times higher rates of pancreatic, kidney, and small intestinal cancers, as well as liver cancer in females, compared to the 1955 birth cohort.

"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," the news release stated.

Although the study has identified cancer trends associated with these birth cohorts, they have not uncovered the exact reasons behind the trend.

The researchers believe that it might be because of unique social, economic, political, and climate environments shared by the birth cohorts, which could affect their exposure to cancer risk factors during their developmental years.

"The increase in cancer rates among this younger group of people indicates 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," said Dr. Ahmedin Jemal, senior author of the study.

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