Other issues include a failure of people “to get started with screening when they reach the appropriate age,” the doctor said. “In 2016, only about 49 percent of adults aged 50 to 54 had been screened.” Another obstacle is that all too often, people go to the doctor only when they’re sick. They’re not focused on preventive care, Dr. Wender said, and neither are many of their doctors.

How the American medical system is organized is yet another obstacle. The typical visit to independent primary care doctors is spent on diagnosis and treatment with little time left for prevention. By contrast, in the Kaiser Permanente system, which has a strong financial incentive to keep its members healthy, 80 percent of members throughout the system — and 90 percent of members on Medicare — have undergone screening for colorectal cancer.

Colorectal cancer is the second most common cause of cancer deaths in this country, with more than 51,000 people expected to die of the disease this year. Although the overall death rate has been dropping for several decades, thanks largely to increased detection and removal of precancerous polyps, deaths among people younger than 55 have increased by 1 percent a year since 2007. This means it’s all the more important to encourage screening among middle-aged adults.

These are the tests currently available:

Colonoscopy. Although this test is the most costly and involved, it is the best not only because it can find an existing cancer, but because it also detects polyps that may become cancer and can be removed during the screening test. It uses a scope and requires a thorough pretest cleansing of the bowel, a step most people find rather unpleasant. But for people without risk factors or a personal or family history of polyps or colorectal cancer, it is usually done only once every 10 years.

FIT. This immunological test, done yearly on a stool sample, checks for blood in the stool, a possible sign of cancer. It usually fails to pick up polyps and thus would not prevent cancer, but it is more effective than the old fecal occult blood test.

FIT-fecal DNA. This test, sold as Cologuard and usually done every three years, combines FIT with markers for abnormal DNA in the stool, making it better able to detect a cancer and advanced precancerous polyps. It misses about half of precancerous polyps.

Virtual colonoscopy. This is an imaging study done every five years via a CT scan that, like an ordinary colonoscopy, requires a thorough bowel cleansing. It visualizes the entire colon, but if anything abnormal is detected, a second prep is needed to permit a regular colonoscopy.