Aasma Shaukat, MD, MPH, on Colorectal Cancer Screening
The American Cancer Society estimates nearly 150,000 new cases of colorectal cancer (CRC) will be diagnosed in the United States in 2020.1 Research has shown that the risk for CRC among younger individuals (those aged 50 years or older) has increased in recent years, which may be cause to start screen at younger ages.2
To answer our burning questions about CRC screening, Gastroenterology Consultant spoke with Aasma Shaukat, MD, MPH, who is the section chief of GI at the Minneapolis Veterans Affairs Health Care System and a professor of medicine at the University of Minnesota.
GASTRO CON: They say a majority of new cases of CRC occur in people aged 50 years or older. Why do recommendations suggest screening earlier, for instance, at age 45 years?
Aasma Shaukat: That is a great question. It is because, looking at our national cancer registry called SEER, we have seen an increase in the incidence of colon cancer in the younger age groups over the last 15 years. That increase is seen in everybody between the ages of 20 to 49 years.
The 45 to 49 age group is the one of most interest, because an increasing incidence of CRC then seems to suggest that, for some reason, cancer rates are going up. Then the natural response is, “Should we do something about this, like start screening earlier?” That was exactly what the American Cancer Society studied for its guideline. The panel did this through a modeling study. Currently, we do not screen 45‑year‑olds. There are no studies showing what that would do. Hence, they relied on modeling studies. Modeling studies use a lot of assumptions. There are a lot of unknowns, so we make up numbers, so to speak, with all their limitations.
These modeling studies used 2 different CRC progression models, both of which suggested that starting screening at age 45 years was cost-effective at a certain threshold. That is probably what formed the basis for why we should start increasing screening.
As some of these publications started showing up in the literature, stating, “Oh, there is increasing incidence of CRC in this younger age group,” there was a pretty big public response and probably an overreaction by the entire community, including gastroenterologists saying that, “We should be very alarmed. We should do this right now.” I think that is what started the trend.
But there are a lot of subtleties that people missed. One of them is that, even though it is true that the incidence has increased by about 17%, the absolute rate is very low. To give you an example, the incidence of CRC among the 50 to 55 age group is 100 per 100,000; whereas the incidence is 1 in 1000 in the 45 to 49 age group. We see 10 per 100,000—meaning 1 in 10,000—a fraction of that risk.
Even if that risk increases from 1 in 100,000 to 2 in 100,000, at a population level, that is minuscule even though it doubled. People hear that the number doubled, but they do not see what that doubling really means and how many more cancers we are actually seeing.
GASTRO CON: The guidelines still recommend screening starting at age 50 years. Are there any new recommendations?
AS: The only new one is regarding patients who are black; the recommendation is to start screening at age 45 years. That demographic has a higher incidence of CRC than patients who are white at any age. Also, the screening rates are lower among patients who are black. For those reasons, we want to bring those patients through the door a little earlier.
GASTRO CON: Can or should CRC screening go beyond 75 years of age? When can gastroenterologists make that call?
AS: Screening can go beyond 75 years. The only difference is that screening should be an individualized decision for patients between the ages of 76 to 85 years. People’s health deteriorates with age, particularly in their 70s. We need to be selective as to who we are screening in that age group. It also depends on whether the patient has been screened before.
If the answer is yes, then it is a risk‑benefit ratio. The benefit is a lot smaller because they have already been screened and identified as a low‑risk person, but the harms are larger. Do they have a 10‑year life expectancy? Again, at that age, individuals have a lot more comorbidities. It is very important to take those into account. At that age, it is a term called “competing risks.”
Screening for CRC might be largely irrelevant, as they are dealing with a lot of other active medical issues—for instance, active cancer or something that decreases their life expectancy to less than 10 years. If they do not have a 10‑year life expectancy, all we are doing is exposing them to a lot of potential harms; we are not giving them the benefit because they are unlikely to benefit.
From age 76 to 85 years, it should be an individualized decision based on the patient's health, their screening history, and their life expectancy. Then after age 85 years, the harms outweigh benefits, no matter how you look at it. Very few people who live 10 more years beyond age 85 are healthy and would actually benefit from screening. At least, the US Preventive Services Task Force recommends no screening after age 86.
GASTRO CON: You talked about how screening after age 75 years needs to be individualized. What factors go into that decision?
AS: These recommendations are for average‑risk individuals who have no symptoms. Individuals who report any symptoms—abdominal pain, diarrhea, blood in the stool, weight loss, anemia—should promptly receive a colonoscopy. Then I would be looking for something else that is worrisome, including CRC. Now, the benefit outweighs the risks.
Individuals with symptoms or those with a very strong family history remain at high risk of cancer. Those individuals should not be cut off as long as they have reasonable life expectancy and no active cancer or other contraindications. Those individuals should be closely monitored. Individuals who have been screened before and had a high-risk lesion or an advanced polyp on that examination or had an early cancer that was removed, they continue to remain at high risk for another colon cancer. Those individuals should undergo colonoscopy.
GASTRO CON: What is the key take-home message here?
AS: One exciting development, and I think where the future is going to lie, is not considering age as an absolute by itself. A number is a number, so essentially we need to develop a risk stratification model. We use them really well in other medical areas, including cardiology. For instance, we have risk scores to decide who should receive anticoagulation therapy. We also use risk stratification scores in liver disease to decide who can benefit the most from a liver transplant.
This one‑size‑fits‑all model—everybody over the age of 50 years, men and women—is way too simplistic. We have better tools. We know the risk factors. For instance, men have a higher risk than women. People who smoke, have a high body mass index, and have poor dietary and lifestyle risk factors are at higher risk for CRC. Putting all of those into a model where it is not just about the age will really tell us who should receive screening and who should not.
- Key Statistics for Colorectal Cancer. American Cancer Society. Revised January 8, 2020. Accessed April 28, 2020. https://www.cancer.org/cancer/colon-rectal-cancer/about/key-statistics.html
- Patel SG. Rising burden of CRC in young adults: an urgent need to address the issue [published online March 18, 2020]. Gastroenterology Consultant. https://www.consultant360.com/exclusive/gastroenterology/rising-burden-crc-young-adults-urgent-need-address-issue