This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
There has been increasing attention directed towards the rising rate of colorectal cancer in younger age groups. In the United States, there was a 51 percent increase in colorectal cancer incidence in adults younger than 55 years old between 1994 and 2014. Partly in response to this alarming trend, the American Cancer Society (ACS) lowered the recommended age at which to begin screening from 50 to 45. Several screening options exist, although the two prominent ones in the United States are colonoscopy and fecal immunochemical tests (FIT), stool tests that detect small amounts of blood. In practice, FIT is used to select a subset of patients for colonoscopy—those with a higher amount of blood in the stool than the threshold set by the laboratory, as blood in the stool is commonly associated with cancer.
A natural response to the rising rate of young adults with colorectal cancer is to start screening asymptomatic people at younger and younger ages, in the hope of detecting cancer at an earlier, more treatable stage, as well as detecting precancerous polyps that can be removed during a colonoscopy. Unfortunately, this strategy is costly and burdensome to young adults; compliance is likely to be poor.
Offering colonoscopies to younger and younger patients in an attempt to reduce a still rare (but increasing) cancer is fraught with issues. While 45 may be a reasonable age to start, as the ACS suggests, there should be little enthusiasm for moving the recommended age for screening to 40 or 35. For example, the risk of developing colorectal cancer between the ages of 35 and 39 is approximately 1 in 2000 over the course of five years (about six times lower than for age 50 to 54). As such, to detect one cancer it would be necessary to have thousands of young men and women undergo colonoscopies, which typically involves a day or more of bowel preparation, another day lost from work due to sedation, a small risk of adverse events from the procedure, and a cost of approximately $1600. It is clear that if we target younger and younger patients with an invasive screening test in an attempt to detect rarer and rarer cancers, at some point the cost and burdens of the test will significantly outweigh the benefit.
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In addition, while compliance with colorectal cancer screening is suboptimal in all age groups, it tends to be worse at younger ages. In the U.S., where compliance with colorectal cancer screening is approximately 68 percent in the over-65 age group, compliance is only 58 percent at ages 50 to 64. It is likely that the participation rate will be even lower in younger adults. This is unfortunate because colorectal cancer, which is the second leading cause of death in the U.S., responds very well to treatment when it is detected at an early stage, with a 90 percent five-year survival rate. A more convenient option is needed, such as a blood test that can be performed during a routine health check.
To make significant strides in preventing morbidity and mortality from early-age colorectal cancer, we need a more convenient screening option. Scientific progress in blood-based cancer detection may offer a solution. Recent results from multiple groups should make us optimistic that screening for colorectal cancer and polyps with a blood test may be feasible in the near future.
For example, at this year’s American Society of Clinical Oncology Gastrointestinal Symposium, investigators from Taiwan reported that a commercially available blood test that detects circulating tumor cells was positive in 87 percent of patients with colorectal cancer and 76 percent of patients with precancerous polyps. Our group is planning a large scale prospective study that we hope will confirm these results and demonstrate that blood-based screening might work for all age groups.
Early detection is critically important to curing cancer. Although lowering the recommended age for colorectal cancer screening is a step in the right direction, it is unlikely to be enough to dramatically reduce colorectal cancer mortality. To increase early cancer detection, we need to improve compliance, and to improve compliance, screening needs to be convenient and affordable. A blood test that can be done without preparation during a routine clinic visit would go a long way towards achieving this goal.