In the wake of Chadwick Boseman’s death from colon cancer at age 43, many people have questions about the disease, especially about the risk of colon cancer in younger people. Here’s what is known and what experts recommend.

Doesn’t colon cancer mostly affect older people?

Although the majority of cases are found in older people, there has been an increase in cases in younger people in recent years.

Among people over 65, rates of colorectal cancer, which includes tumors in the rectum or the colon, have actually been declining, probably because of more regular screening. Nonetheless, it is the second-leading cause of cancer deaths in the United States for men and women combined, and cases have been rising by about 2 percent annually in recent years in people under 50, according to a recent report by the American Cancer Society.

Experts aren’t sure exactly why. For some patients, obesity, diabetes, smoking or a family history of cancer may play a role, but not all people who develop colorectal cancer have these risk factors.

“The bottom line is we just don’t know,” said Dr. Robin B. Mendelsohn, co-director of the Center for Young Onset Colorectal Cancer at Memorial Sloan Kettering Cancer Center, which was opened in 2018 to treat younger patients and study the reasons for their diagnoses. She and her colleagues are exploring whether diet, medications like antibiotics, and the microbiome — which have all changed significantly for generations born in the 1960s and later — might be contributing to the cancer in younger people.

When is screening recommended?

Everybody should begin getting screenings at age 45, the American Cancer Society and other expert groups recommend. But people with a family history of colon cancer should start getting tested at age 40, or at 10 years younger than the age at which their family member was diagnosed, whichever is sooner.

Dr. Mendelsohn recommends early screening also for people with a history of inflammatory bowel disease, like ulcerative colitis or Crohn’s disease, and for people who have previously received radiation in their abdomen or pelvis.

Screenings can be done with various tests on stool samples or with imaging-based tests like colonoscopies. The risks from these tests are relatively small. The prep for a colonoscopy, drinking liquid to cleanse the colon the day before, can be uncomfortable. But the advantage of a colonoscopy is that if it reveals polyps that might be precancerous, they can be removed during the test, said Dr. Mohamed E. Salem, an associate professor of medicine at the Levine Cancer Institute at Atrium Health in Charlotte, N.C.

“It makes a huge difference when you detect cancer early versus late,” he said.

“The five-year survival rate for young people for early-stage disease is 94 percent,” said Rebecca L. Siegel, the scientific director of surveillance research at the American Cancer Society. For people with late stages of the disease, the survival rate can be as low as 20 percent, she said. Early diagnosis, Ms. Siegel said, is “the difference between life and death.