A new study of recent trends in colorectal cancer in the United States confirms that rates among those under the age of 50 years are rising. The findings also reveal that diagnoses of colorectal cancer in younger adults are more likely to be of advanced disease.
Previous investigations have shown that rates of colorectal cancer in the under 50s have risen since the 1970s.
For their study, Dr. Boone Goodgame, an assistant professor in the departments of internal medicine and oncology at the University of Texas at Austin, and his colleagues focused on more recent trends.
Using data from the National Cancer Database registry, they found that 12.2% of colorectal cancer diagnoses in the U.S. in 2015 were in people under the age of 50 years compared with 10% in 2004.
The team also found that the percentage of colorectal cancer diagnoses in younger individuals went up in urban but not rural regions.
In addition, doctors detected signs of advanced disease in more than half (51.6%) of colorectal cancer diagnoses in younger adults compared with 40% in the over 50s.
Colorectal cancer diagnoses in younger adults increased at the same rate across all income levels. However, the highest percentage of diagnoses was among the highest earners.
The team reports the study findings in a recent Cancer journal paper.
"Several studies have shown that the rates of colorectal cancer in younger adults have risen slowly in the U.S. since the 1970s," says Dr. Goodgame, who was senior author of the study.
"[B]ut, for practicing physicians, it feels like we are seeing more and more young people with colorectal cancer now than we were even 10 years ago," he adds.
Deaths to colorectal cancer have been falling
Colorectal cancer develops when cells in the colon or rectum grow out of control and form a mass, or tumor.
Often, the cancer starts as a polyp, or small growth, on the innermost layer of the wall of the colon or rectum.
Most polyps do not become cancerous, but those that do can take years to reach that stage.
If cancer does develop in a polyp, it can grow and invade other layers of the colon or rectum wall. From there, cancer cells can break away and travel through blood or lymph vessels to other parts of the body and set up secondary tumors.
The vast majority of colorectal cancers are of the adenocarcinoma type. These begin in the cells that make the lubricant, or mucus, that covers the lining of the colon and rectum.
Not counting cancers of the skin, of the cancers that doctors diagnose in both women and men in the U.S., colorectal cancer is the third most common, according to the American Cancer Society (ACS).
In 2019, the ACS estimate that 145,600 people in the U.S. will find out that they have colorectal cancer, and 51,020 will die of the disease.
Rates of death from colorectal cancer in the U.S. have been falling in both women and men for dozens of years. Today, there are more than 1 million people living in the U.S. who have survived colorectal cancer.
Lowering screening age
The ACS suggest that the likely reasons for the fall in colorectal cancer deaths are improved screening and treatment. Improved screening generally means earlier diagnosis, which increases the likelihood of successful treatment.
Commenting on the recent findings, Dr. Goodgame says that "just last year," many guidelines for colorectal cancer screening changed the recommended starting age from 50 to 45 years.
The ACS guidelines, for example, recommend that adults aged 45 years and older who are at average risk for colorectal cancer should have regular screening tests. The screening should either be an examination using colonoscopy or a test for signs of cancer in fecal samples.
However, Dr. Goodgame states that "most physicians and patients don't appear to be following those recommendations."
He notes that it is not clear what is causing the rise in colorectal cancer rates among younger adults in the U.S. However, recent studies are beginning to point to alterations to gut bacteria and an increase in the number of people who are overweight or have obesity.
In a linked editorial, Dr. Chyke A. Doubeni, a member of the U.S. Preventive Services Task Force, suggests that more rigorous research is necessary to inform decisions on whether changing the screening age for colorectal cancer would be appropriate.
"Because the number of colorectal cancer cases from inherited causes are much higher in younger individuals, it is unknown whether screening for sporadic cases in a group with such low disease rate can result in a favorable balance of harms and benefits."
Dr. Chyke A. Doubeni