Colorectal cancer (CRC) epidemiology is changing due to a birth cohort effect, also called birth cohort CRC — the observed phenomena of the rising risk for CRC across successive generations of people born in 1960 and later — according to a new narrative review.
Birth cohort CRC is associated with increasing rectal cancer (greater than colon cancer) diagnosis and distant-stage (greater than local-stage) CRC diagnosis, and a rising incidence of early-onset CRC (EOCRC), defined as occurring before age 50.
Recognizing this birth cohort effect could improve the understanding of CRC risk factors, etiology, mechanisms, as well as the public health consequences of rising rates.
“The changing epidemiology means that we need to redouble our efforts at optimizing early detection and prevention of colorectal cancer,” Samir Gupta, MD, the review’s lead author and professor of gastroenterology at the University of California, San Diego, California, told this news organization. Dr. Gupta serves as the co-lead for the cancer control program at Moores Cancer Center at UC San Diego Health.
This requires “being alert for potential red flag signs and symptoms of colorectal cancer, such as iron deficiency anemia and rectal bleeding, that are otherwise unexplained, including for those under age 45,” he said.
We also should make “sure that all people eligible for screening — at age 45 and older — have every opportunity to get screened for colorectal cancer,” Dr. Gupta added.
The review was published online in Clinical Gastroenterology and Hepatology.
Tracking Birth Cohort Trends
CRC rates have increased in the United States among people born since the early 1960s, the authors wrote.
Generation X (individuals born in 1965-1980) experienced an increase in EOCRC, and rates subsequently increased in this generation after age 50. Rates are 1.22-fold higher among people born in 1965-1969 and 1.58-fold higher among those born 1975-1979 than among people born in 1950-1954.
Now rates are also increasing across younger generations, particularly among Millennials (individuals born in 1981-1996) as they enter mid-adulthood. Incidence rates are 1.89-fold higher among people born in 1980-1984 and 2.98-fold higher among those born in 1990-1994 than among individuals born in 1950-1954.
These birth cohort effects are evident globally, despite differences in population age structures, screening programs, and diagnostic strategies around the world. Due to this ongoing trend, physicians anticipate that CRC rates will likely continue to increase as higher-risk birth cohorts become older, the authors wrote.
Notably, four important shifts in CRC incidence are apparent, they noted. First, rates are steadily increasing up to age 50 and plateauing after age 60. Rectal cancers are now predominant through ages 50-59. Rates of distant-stage disease have increased most rapidly among ages 30-49 and more slowly decreased among ages 60-79 compared with those of local-stage disease. In addition, the increasing rates of EOCRC have been observed across all racial and ethnic groups since the early 1990s.
These shifts led to major changes in the types of patients diagnosed with CRC now vs 30 years ago, with a higher proportion being patients younger than 60, as well as Black, Asian or Pacific Islander, American Indian/Alaska Native, and Hispanic patients.
The combination of age-related increases in CRC and birth cohort–related trends will likely lead to substantial increases in the number of people diagnosed with CRC in coming years, especially as Generation X patients move into their 50s and 60s, the authors wrote.