Colorectal cancer, long considered a scourge of the aged, has been steadily rising among young and middle-aged adults in the United States, new research shows.
A study released Tuesday by researchers from the American Cancer Society and the National Cancer Institute found that a typical American millennial born in 1990 is, in any given year of her life, twice as likely to be diagnosed with colon cancer as a person born in 1950. And compared to that older baby boomer, the average twenty-something is four times as likely — again, at every age — to be diagnosed with cancer of the rectum.
That picture emerged from the records of almost 500,000 people age 20 and older who were diagnosed with colon or rectal cancer between 1974 and 2013. Published in the Journal of the National Cancer Institute, it's the first study to examine population trends in colorectal cancer since 1990, just a few years after colonoscopy screening for those over 50 became widespread.
Those findings were reinforced Wednesday in a related report on colorectal cancer from the American Cancer Society. Among Americans 50 and older, cases of colon and rectal cancer have dropped 32% since 2000, largely due to screening, the report says. Meanwhile, cases among Americans younger than 50 rose 22% during the same period.
In addition, the mortality rate due to these cancers fell 34% in the older group and rose 13% in the younger group between 2000 and 2014, according to the report in CA: A Cancer Journal for Clinicians.
The disturbing new picture casts a shadow on what seemed hopeful progress. With the growing use of colonoscopy, new cases of colon or rectal cancer have been steadily declining among Americans since the mid-1980s. Today, about 135,000 new cases of colon or rectal cancer are diagnosed each year in the United States, down from 160,000 a decade ago.
But that decline has been driven by people over 50, who were both most likely to develop these cancers and most likely to be screened via colonoscopy.
Meanwhile, new diagnoses of colon and rectal cancer among patients in their 20s, 30s, and 40s have been on the rise.
The Journal of the National Cancer Institute study from Tuesday found that for adults 20 to 39, rates of colon cancer increased by 1% to 2% per year from the mid-1990s through 2013. In adults 40 to 54, colon cancer rates rose by 0.5% to 1% per year during the same period.
Even more dramatic increases were seen in the rate of rectal cancer among younger patients, and those increases have been mounting over a longer period. In adults 20 to 29, rates of rectal cancer rose about 3% per year between 1973 and 2013. In adults 30 to 39, rectal cancer rates grew 3% per year between 1980 and 2013. And in adults 40 to 54, rectal cancer rates increased by 2% per year between the 1990s and 2013.
What is driving those numbers is still unknown, experts say. The rise in diagnoses among younger patients has tracked closely with the rise of obesity in the United States, and obesity is a risk factor for colon and rectal cancer.
But other risk factors, including a sedentary lifestyle, excessive alcohol consumption and infectious diseases such as human papillomavirus could be playing a role.
"It's still a disease of older folks," said Dr. George J. Chang, chief of colon and rectal surgery at the University of Texas M.D. Anderson Cancer Center.
The American Cancer Society report released Wednesday estimates that 135,430 Americans will be diagnosed with a colorectal cancer in 2017, and 50,260 of them will die from it. About 10% of these new diagnoses and 7% of the deaths will occur in people younger than 50.
Americans younger than 50 have a roughly 1 in 300 chance of developing invasive colorectal cancer. But the risk rises with age, and by the time they're in their 70s, the chances are about 1 in 30, according to a 2016 report in CA: A Cancer Journal for Clinicians.
But with a growing number of younger patients affected, physicians and patients need to be more open to the possibility that symptoms such as blood in the stool and changed bowel habits could be signs of cancer, he said.
Dr. Chang also suggested that routine colorectal cancer screening might need to be extended to certain people under 50.
These younger patients are far less likely than older ones to get a colonoscopy that catches a polyp before it becomes cancer, or before a malignant mass breaks through the gastro-intestinal wall and spreads elsewhere. As a result, the study found, their cancers are 58% more likely to be diagnosed after spreading beyond the rectum or colon compared with patients over 50.
Allison Rosen of Houston hopes to be more than a grim statistic. Diagnosed with colon cancer at age 32 after enduring years of intestinal ills, Rosen has become a cancer outreach and education coordinator at Baylor University College of Medicine. By the time her doctor detected the mass in her colon, it was close to breaking through the intestinal wall and spreading.
"Cancer was not on my radar and was definitely not on my doctor's radar," said Rosen, who is now 36 and, after several complications, cancer-free. "I was lucky I insisted on having that scope."
Rosen now warns anyone who sees blood in the toilet after a bowel movement to investigate further.
"Being your own advocate is huge," she said. "It's sad when I hear of a young adult being ignored by a doctor saying it's hemorrhoids. If you don't know what it is for sure, then figure it out."
Younger patients are still more likely to survive their ordeal, because they tend to be in better health than older patients and can tolerate aggressive treatment. But they will carry an increased cancer risk into middle and older age, said study leader Rebecca Siegel, an epidemiologist at the American Cancer Society.
Siegel noted that for young people, a diagnosis of rectal or colon cancer remains a rare event.
"We don't want to be putting fear into people, telling them they have a high cancer risk if they're in the 20s or 30s," Siegel said. "But the magnitude of the increase is striking, as is the duration of that increase."
Moreover, she added, the disease's youngest victims may offer the clearest answer to the question of why these cancers are striking at younger ages.
"This is a cohort effect which typically reflects changes in behaviors that influence cancer risk. So if we don't figure out what's going on, it will continue."
Times staff writer Karen Kaplan contributed to this report.
March 1, 10:50 a.m.: This story has been updated to include information from an American Cancer Society report released Wednesday.