Among older people, cancers of the colon and rectum are declining. But in a disturbing and mystifying trend, researchers are seeing a sharp rise in the number of younger people, including those in their 30s and even 20s, being diagnosed with colorectal cancer.
In a study released earlier this year, the American Cancer Society found that colorectal cancer rates have steadily dropped for those born before 1950. But for every generation born after 1950, the rates are rising. Rates of rectal cancer are rising particularly sharply, the study found. According to one of the study’s authors, a person born in 1990 had double the risk of colon cancer, and quadruple the risk of rectal cancer, as a person born in 1950.
For the colorectal cancer decline in older people, scientists have a simple explanation: routine colon cancer screening for people 50 and older has led to disease being caught and treated early, in many cases before it even becomes cancer.
Theories, but no certain explanation
For the second trend, experts have no real explanation. “The incidence of colon cancer is rising in younger people and it’s not clear why,” says Rocky Mountain Cancer Centers oncologist Sujatha Nallapareddy, MD , who specializes in treating colorectal cancers. “There are some theories, but we think there could be multiple reasons.”
One theory is the increase in Type 2 diabetes in younger adults; another is the increased use of antibiotics, which upset the natural balance of microbes in the gut.
Others have speculated that unhealthy changes in diet, such as eating more fast food, more sugar and more processed meats, may be contributing.
So far, none of those theories have been corroborated by research, Dr. Nallapareddy says. Without a clear answer, more studies are needed.
Overall, factors that increase colorectal cancer risk include:
- Being overweight or obese
- Physical inactivity
- A diet high in red meat
- Excessive alcohol consumption
- Family history
- A history of type 2 diabetes
Colorectal cancer remains the third most common cancer in both men and women. The American Cancer Society predicts that more than 137,000 people will be diagnosed with the disease in the U.S. this year. Men are slightly more likely to develop colon cancer than women.
Because younger people aren’t screened for colorectal cancer, and because most physicians don’t expect to see it in people in their 20s or 30s, the cancer is often in advanced stages by the time they are diagnosed.
The study has prompted some to call for earlier routine screening. Currently, the American Cancer Society recommends testing starting at age 50 for most people, with screening starting at a younger age for those with a family history of colon or rectal cancer.
Dr. Nallapareddy says she’s not ready to recommend routine screening for younger people. And in fact, 90 percent of colon cancer cases still occur in those 50 and older. But she does caution people of all ages to be aware of colon cancer symptoms, which include:
- A change in bowel habits, such as diarrhea, constipation, or narrowing of the stool, that lasts for more than a few days
- A feeling that you need to have a bowel movement that is not relieved by doing so
- Rectal bleeding
- Dark stools, or blood in the stool
- Cramping or abdominal (belly) pain
- Weakness and fatigue
- Unintended weight loss
“What I would say is not to ignore the possibility,” Dr. Nallapareddy says. “I know if a 30-year-old comes in with bleeding, many primary care physicians will say it’s hemorrhoids. I would suggest those physicians be more vigilant — if patients are symptomatic, do a colonoscopy regardless of age.”
Until further studies uncover more about the causes, both physicians and patients need to be proactive and vigilant.