Rates of rectal cancer are rapidly rising among American adults under the age of 65, according to a new study from the American Cancer Society.
Federal data shows that rectal cancer now makes up nearly a third of all colon and rectal cancer diagnoses, with rates of diagnosis rising from 27 percent in the mid-2000s to 32 percent this year.
The increase in rectal cancer is largely being driven by tumors in the last section of the colon next to the rectum, also known as the distal colon.
The distal colon is on the left side of the abdomen, and about 70 percent of colorectal cancers are diagnosed on the left side, according to the Texas-based MD Anderson Cancer Center. Left-sided cases are more easily detected during colonoscopies.
Case numbers are increasing for all colorectal cancer cases. The new report showed that 45 percent of new colorectal cancer cases are in adults under 65 – up from 27 percent in 1995. Colorectal cancer is now the second-most common cause of cancer deaths in the U.S., with more than 158,000 new cases and 55,000 deaths expected this year.
The reason for these trends largely remains a mystery to oncologists. Most experts don’t think the cause is genetic so it must be related to “something we’re doing or some other exposure,” Rebecca Siegel, the society’s senior scientific director, said in a statement.
“We need to redouble research efforts to understand the cause but also circumvent deaths through earlier detection by educating clinicians and the general public about symptoms and increasing screening in people 45-54 years,” she added.
Part of the reason that rates have risen in younger adults is because the screening age was lowered to 45 in 2021. But that doesn’t account for the decades-long surge.
Researchers have previously tied Americans’ ultra-processed diet and sedentary lifestyle to the shift. Lifestyle factors are attributable to more than half of colorectal cancers, according to the society.
Past research has also identified a potential link to a toxin in the gut that can inflict DNA damage on colon cells. Colibactin, which is produced by harmful species of gut bacteria, can inflict DNA damage on colon cells that can lead to the development of cancer.
And misdiagnosis certainly doesn’t help. Younger patients often face diagnosis delays because their symptoms are mistaken for hemorrhoids or other benign conditions, Dr. Lynn O’Connor, chief of colon and rectal surgery at Mercy Medical Center in New York, told ABC News.
“There is significant misdiagnosis,” she said, “These are young patients, it’s not on the radar. They have to see at least two to three doctors before they get a diagnosis.”
Detecting colorectal cancer early is crucial, as it dramatically improves survival rates and allow doctors to remove precancerous growths before they become harmful.
But only 37 percent of Americans between the ages of 45 and 49 are getting screened, the society’s report showed.
“These findings further underscore that colorectal cancer is worsening among younger generations and highlight the immediate need for eligible adults to begin screening at the recommended age of 45,” Dr. William Dahut, the society’s chief scientific officer, said.
