The American Cancer Society updated its colorectal (colon and rectal) cancer screening guidelines last week. It now recommends that adults at average risk for the disease begin screening at age 45 rather than age 50, as the organization had previously recommended.
The updated guidelines stress that the screening test doesn’t have to be a colonoscopy or other invasive exam. It can also be one of several home stool tests, which are available by prescription. All positive results on non-colonoscopy tests, however, should be followed up with a colonoscopy, the guidelines stress.
It’s not clear if other medical groups will follow the cancer society’s lead on this issue, particularly since its recommendations are based on statistical modeling, not on the much more rigorous evidence of clinical trials.
Other organizations that have issued colorectal cancer screening guidelines, including the U.S. Preventive Services Task Force (USPSTF), recommend that routine screening for average-risk people start at age 50.
Increasing among younger adults
Colorectal cancer is the fourth most commonly diagnosed cancer among adults in the United States, and the second-leading cause of cancer-related deaths. This year, more than 140,000 Americans will be diagnosed with the disease, and about 50,000 will die from it.
The majority of colorectal cancers occur in people over the age of 50. In the U.S., the average age for a colon cancer diagnosis is 68 for men and 72 for women, according to the American Society of Clinical Oncology. The average age for a rectal cancer diagnosis is age 63 for both men and women.
Recent research, however, has reported an increase in the incidence of colorectal cancer — particularly rectal cancer — among younger adults. These cancers have increased 51 percent among adults under age 50 since 1994. Currently, about 11 percent of all colorectal cancer diagnoses are in this younger age group.
As a study published last year reported, someone born around 1990 is about twice as likely to develop colon cancer and about four times more likely to develop rectal cancer during their lifetime as someone born around 1950. Researchers don’t know why, although the obesity epidemic and changes in the American diet are frequently cited as possible causes.
To find out more about these troubling trends — and how they figured into the American Cancer Society’s updated screening recommendations — MinnPost spoke with Timothy Church, one of the authors of the new guidelines and a professor of environmental health sciences at the University of Minnesota School of Public Health. An edited version of that conversation follows.
MinnPost: Why did the American Cancer Society decide to update its colorectal cancer screening guidelines?
Timothy Church: The U.S. Preventative Services Task Force published their updated guidelines [in 2016], so we thought this was a good time for us to update our guidelines as well. We started looking at the data, including the incidence rates for colorectal cancer, especially among younger people. We decided that we would delve into that issue a little deeper since there was more information available than the USPSTF had when they did their analysis.
MP: What did you find?
TC: [The incidence rates] were going up in people less than age 55, whereas in the last decade they’ve been going down for older people. In fact they’ve been going down so fast [among older adults] that we are actually seeing fewer deaths from colorectal cancer, not just fewer cases of colorectal cancer, than we have in the past.
MP: What do you attribute that trend to? More widespread screening?
TC: It is due in part to screening. In terms of the mortality rate, there are various estimates of how much of it is due to screening and how much of it is due to improved treatment. In terms of the incidence rate, it’s probably due predominantly to screening because screening is really the only way to have that big an impact on the incidence of colorectal cancer.
MP: Is that because screening helps identify precancerous polyps, which can then be removed?
TC: Precisely. And so that’s what caused us to look at this very carefully. One of my first thoughts [about the rising incidence rate among younger adults] was that this was just due to the fact that younger people are getting more colonoscopies. Colonoscopy is so much more available now, and they’ll do a colonoscopy for a lot of different reasons now [such as a family history of colon cancer], so it may just be incidental findings. But the more we looked at the data, the more it looked like a real increase and not just a screening effect or an incidental finding effect in young people. So, we asked CISNET [the Cancer Intervention and Surveillance Modeling Network] to do some modeling based on starting screening at 45 and 40 to see if it would be more effective — or as effective — to screen in that group as it has been to screen in the older group.
MP: Why did you go down only to age 40?
TC: If you look at the incidence rates for 20- to 29-year olds, they’re only about one per hundred thousand. That’s very, very little compared to, say, 70-year-olds, who have an incidence rate of about 150 to 325 per hundred thousand. That’s over a hundred-fold difference in the rates, which is why we focus on the older folks. You don’t expect screening to be effective if you’re screening a population that has a very low incidence of the disease. But when you start getting up toward age 50, then you’re starting to talk about rates that are getting into the neighborhood of the incidence rates of older people. So we thought that was a reasonable place to work and to look more deeply.
MP: And what did you find regarding people in their 40s?
TC: In the simulation we found the 40- to 44-year-olds did not benefit nearly as much as the people 50 and older. However, in the individuals 45 to 49 we found a very comparable beneficial effect. Now keep in mind, these are only simulations. We didn’t have randomized trials like we have for the older folks to depend on in terms of solid evidence. But we also realized that there were never going to be randomized trials in that age range, and so this is what we were stuck with. So, we looked very carefully at the data and concluded that in all likelihood, people 45 to 49 would benefit [from screening] about as much as the people 50 to 54 or 55 to 59. So we decided to make the recommendation. We firmly believe that this is going to benefit a new group of people and will lead to lower losses of life and much less suffering from disease.
MP: One of the theories about why the incidence of colorectal cancer has been increasing in younger people is that obesity is so much more of a problem today than it was in the past. What do you think?
TC: No. It doesn’t come close to explaining the increases we’re seeing.
MP: What, then, do you think is behind the increase?
TC: Some of it is the increased availability of colonoscopy. It used to be that symptoms had to be pretty extreme before you got a colonoscopy. Today, many younger people are getting colonoscopies for other indications, and then they’re just finding, incidentally, colon cancer. We’ve also been recommending for years that younger people who have a family history [of colon cancer] get screened at a younger age. But, as with obesity, [that’s] not enough to explain the increase we’re seeing. So, it could be diet. It could be an unknown environmental contaminant that we’re just not aware of yet. It could be changing demographics. In the end, we may find out it’s a variety of factors that just happen to work together to create these rather alarming increases. I hope it’s not that, because that makes it that much harder to deal with. I would always prefer a single explanation so that we can address that cause. But I’m not sure that’s what we’re going to find.
The other aspect of this is we don’t really have enough follow-up yet on this younger age group to know whether their rates of deaths from colorectal cancer are also going up. There’s some hint that they might be, but you would expect a delay in an upturn of deaths after an upturn in incidents, because it just takes time for people to die. And so we’re not sure yet about the impact on mortality. It could be that the impact on mortality is not as big as the impact on incidence, or it could be just as dramatic. We just don’t know yet.
MP: What are the key symptoms of colorectal cancer — the ones people of all ages shouldn’t dismiss?
TC: Bleeding is the big one. You should never ignore blood in your stool. If you find blood in your stool, always see a doctor. Also, if you have a family history [of colorectal cancer], tell your doctor. You probably should get screened earlier and perhaps more often.
MP: Let’s get to the recommendations. You encourage patients to discuss with their doctors all screening options for colorectal cancer — not just colonoscopy — and to choose the option that they’re most comfortable with. That includes three types of home stool tests.
TC: Yeah. That’s our snappy way of saying that the best test is the test that you’ll do.
MP: Because so much of the emphasis has been on colonoscopies over the past decade or so, I think many people are surprised to find out that the home tests are also a reliable screening tool.
TC: Every way we’ve looked at those tests, they seem to have about the same ratio of potential harm to benefit as just going straight to colonoscopy. Colonoscopy certainly wins in terms of being able to find every cancer and that sort of thing, but the others are very good at getting you to colonoscopy if you are at risk, and over a long period of time, they catch up. We suggest that people talk to their doctor and that the doctor actually have at least two options for each individual so that if, for example, the physician wants to promote colonoscopy and the person is not comfortable doing that, they’ll have another thing that they can recommend that’s not as invasive or that’s more acceptable to the person and their perception of their own risk. Preliminary research suggests that you’ll get the highest compliance with screening recommendations by offering choices.
MP: Screening comes with risks. What are those?
TC: Well, in terms of just physical risk, there’s a potential with colonoscopy for bleeding after the procedure and for perforation of the colon. There’s also some potential of the procedure triggering a fatal or non-fatal cardiac event in people with an underlying heart condition. For each procedure the risk is very low, but when you’re doing a hundred million of them, the total risk is no longer negligible. So, when we’re thinking about public health, we have to think about it in those terms rather than the risk to a particular individual.
We can’t totally ignore cost, either. We don’t address it in this paper, but obviously the more people we screen, the more money we’re going to have to spend on the screening process. We’d like to spend that money only where it’s effective, and so we don’t want to overuse a technology in areas where it’s not actually going to benefit. The really disappointing thing is that there are a lot of people who should be getting more colonoscopies who aren’t, especially those people who’ve had polyps removed and should be looked at more frequently. Often those people go without the additional colonoscopies.
But I think the biggest issue is that only about two-thirds of the population [for whom screening is recommended] is getting screened. That means a third of the population is not getting the benefit of screening. That adds up to a lot of deaths and a lot of cases of colorectal cancer that are preventable. And so our biggest goal is to get everybody to get the message, to convince as many people as we can that they should be getting screened and to try and make that as easy and simple and straightforward for them as we possibly can.
MP: This is a pretty treatable disease if caught early.
TC: That’s correct. These numbers may be a little out of date, but, roughly, if you’re diagnosed in stage 4 — the most advanced stage of the disease, with metastasis — your survival rate is somewhere between 5 and 10 percent over five years. So you’ve got a 90 to 95 percent chance of not making it another five years. If you’re discovered in stage 1, your probability of surviving another five years is in excess of 98 percent. If at you’re at stage 2, it’s still very high. It’s in excess of 94 percent. And so the difference between being diagnosed when it’s small and contained and being diagnosed when it’s spread all over the body is very dramatic. Even if you catch it in stage 3 instead of stage 4 — and that’s the difference between it just spreading to the lymph nodes in your body versus spreading all over the body — you’ve got a 50 percent chance of survival.
Colorectal cancer is extremely treatable if you catch it early. It’s a nasty disease if you catch it very late. So, the most important thing is for people who are in the recommended age range to get screened. If you don’t have a regular doctor, call your clinic. Ask who you need to talk to about getting screened. Maybe you don’t like colonoscopy. Maybe you don’t like the stool test. Do a CT colonography then. The important thing is to do the screening. It can save your life.