It was a shock to learn that actor Chadwick Boseman had died. The rising star who played Black Panther in the Marvel Cinematic Universe was 43 when colorectal cancer took his life in August 2020. More recently, James Van Der Beek made headlines after he died from the same cancer at the age of 48.
The plural of 鈥渁necdote鈥� may not be 鈥渄ata,鈥� but these two celebrity cases happen to highlight a worrying trend: as rates of colorectal cancer have been going down for older adults, the line has moved in the opposite direction for people under the age of 50, especially men. In fact, if we compare an average adult born in 1990 to one born in 1950, their risk of getting colon cancer is听. For rectal cancer, it鈥檚 four times as high. We will look at what these numbers mean later. Just know that they are not as scary as they look, but they are real.
In dealing with this mystery, we see two different modes of thinking. On one side, we witness scientists and physicians formulating hypotheses, testing them, and seeing contradictory results. On the other side, impatient wellness gurus selling half-baked advice based on preliminary studies. Good scientists understand that research is slow and often hard to parse, while health influencers jump the gun on what guilty party they should blame this week.
The birth cohort effect
Cancer is not a single disease but a whole family. The cells that make up our body divide according to a strictly coordinated molecular ballet. When key figures in this dance are mutated and can鈥檛 do their job, the entire thing spins out of control. The brake pedal in the metaphorical car stops working and the accelerator gets floored. Cells blossom into tumours, and these hungry, deformed masses push against our organs and make us sick. When a tumour taps into our vascular system of veins and arteries by growing its own blood vessels, cancerous cells break away and colonize distant sites in the body, creating metastases. Metastatic or stage IV cancer is the final stage. There is no stage V.
Cancers are named after the organ where they start, and colorectal cancer (CRC) implicates the last stretch of our gut. When our food has been thoroughly blended by our stomach, it moves into the small intestine, a zigzagging serpent densely compacted in the area below our belly button. Once it has absorbed nutrients from this pur茅e, it moves what鈥檚 left of the food into our colon. It鈥檚 a wide tube that goes up our right side, transverses our abdomen, goes down the left side, kinks to the centre of our pelvis, and is joined to our rectum. From there, the anus leads to the outside world. (The term 鈥渓arge intestine鈥� usually includes not just the colon but the rectum, anus, and a pouch known as the cecum as well.)
It takes decades for the wrong mutations to accumulate so that a diagnosable mass of cancerous cells can be seen. This is why cancer is usually tied to ageing. (Childhood cancers have听genetic differences听that make them appear much faster.) Colorectal cancers that are diagnosed in people under the age of 50 are known as early onset (EO-CRC). It is those cases that have been going up lately in so-called Western countries and in countries whose diets have been Westernized in recent decades.
I have seen researchers write of an 鈥渆pidemic鈥� of EO-CRC, but I think it鈥檚 important to look at the numbers from different angles. It鈥檚 easy to fearmonger and equally easy to dismiss. The truth is somewhere in between.
Starting with data from the United States, CRC is听听cancer, after breast, prostate, and lung. This may sound like a lot, but when we look at a single person at average risk for this cancer, their lifetime chances of being diagnosed with it hover around听, which is one chance in 25. By comparison, the lifetime chances of a woman being diagnosed with breast cancer are 13%, or in one in eight.听
In a population of roughly 340 million people, the U.S. see a little听听new cases of colon cancer every year and around 50,000 new cases of rectal cancer. Here in Canada, CRC is also the fourth most common, with a projected听听this year in a population of over 41.5 million people.
Of all these new CRC cases,听听will be diagnosed in someone younger than 50. Flipping this around, it means that the vast majority鈥�90%鈥攐f colorectal cancers are first seen in people over the age of 50, hence the importance of screening in that age group.
But what鈥檚 concerning is that something is causing an increase in the number of younger adults who get diagnosed with CRC, and it has nothing to do with improved vigilance, especially since that age group is not typically eligible for cancer screening. It鈥檚 also not just happening in North America: a听听reported that EO-CRC incidence went up significantly two decades ago. For people in their thirties, it jumped from 2.8 people per 100,000 inhabitants in 2006 to 6.4听per 100,000 in 2016. For people in their forties, the number increased from 15.5 to 19.2 per 100,000 for a similar period of time.
This phenomenon has been termed a 鈥渂irth cohort effect.鈥� In Western countries like Canada and the United States, it affects people born after 1960 or 1970, depending on the source you consult. People with early-onset CRC tend to be听听than those who develop the cancer later in life. They are more likely to be diagnosed because of听symptoms听whereas older adults are more likely to be diagnosed during a听routine screening.听Half of people with EO-CRC complain of abdominal pain, and up to half notice bloody stools. For a third of patients, it鈥檚 weight loss and a change in bowel habits. These cases, compared to older cases, tend to be in the left, descending colon or in the rectum, and they are usually diagnosed at a more advanced stage, with the cancer likely to be more aggressive.
At the molecular level, these early-onset cases are not that much different from the rest. It鈥檚 not like there is one gene that is mutated in all of them and that is left alone in people who develop the cancer at a later age. What is interesting is that, outside of the typical genes implicated in certain forms of colorectal cancer, scientists detect听听in younger adults with the disease. A variant of uncertain significance or VUS is a change in the DNA sequence whose consequence is currently unknown. We see a 鈥淭鈥� where a 鈥淐鈥� should be, for instance, but it鈥檚 unclear what impact鈥攊f any鈥攖his has on the person鈥檚 health. Further work in the next few decades will hopefully start to unfurl these little mysteries.
Identifying risk factors is hard
The question on your mind right now is likely to be, 鈥淲hat can I do to avoid getting colorectal cancer?鈥� The casual answer of 鈥渆at right, exercise a lot, and don鈥檛 be sick鈥� is probably not satisfying. If you are of the right age, you hopefully know about regular screening. Here in Canada, screening is done between the ages of听听(though the Canadian Cancer Society charity recommends screening at听. Colonoscopies are not recommended for this mass screening due to potential for bleeding and perforations and the time and expertise required; instead, an examination that goes less deep into the colon鈥攁 flexible sigmoidoscopy鈥攊s recommended every 10 years, while a poop test looking for the presence of blood is typically done every two years.
But if you are younger than this, you are not getting screened (unless you are known to be at听, meaning, for example, that you have a parent, sibling or child who has had this cancer). So, what can you do?
I wish the studies we currently had provided uncontroverted evidence; instead, every study has a metaphorical asterisk next to its results. Take the gut microbiome, for example. Our colon is teeming with bacterial life. It looks as if this microbial ecosystem听, regardless of the age at which you develop it. In people with the cancer, we see a听听as well as a few species of bacteria being there in greater numbers鈥攏amely听Bacteroides fragilis, Fusobacterium nucleatum, and the phyla Firmicutes and Bacteroidetes. One hypothesis is that some of these bacteria, in digesting sulfur, release hydrogen sulfide, which creates inflammation in the gut as well as damage to the DNA of the cells making up the colon, which eventually helps bring about cancer.
Does this mean we should all eat yogurt and pop probiotic pills every day to ward off colon cancer? The problem is that significantly altering our gut鈥檚 ecosystem is really hard, and doing the equivalent of planting a dozen trees in the Amazon rainforest will not solve the issue. Hype has听superseded facts听when it comes to products aimed at our microbiome. We know these bacteria play a role in CRC, but we have not yet arrived at legitimate, targeted, actionable advice.
Obesity has also been flagged as a risk factor for EO-CRC, but here too the data is murky. How much of a risk is obesity? Different studies come to different numbers; in fact, in听, being obese seems听to听protect you听from developing CRC, although it has been speculated that it鈥檚 because people tend to lose weight due to the cancer before being diagnosed. It could also be that obesity as a whole is not the risk factor but rather听. Even when we zoom out and package obesity as part of a larger phenomenon鈥攎etabolic syndrome鈥攚hich also includes high blood sugar (like diabetes), abnormal levels of fat in the blood (like high cholesterol), and high blood pressure, the association between this syndrome and colorectal cancer yields听听from one study to the next.
We know with听听that high alcohol consumption鈥攅specially the kind of binge drinking all too common in universities鈥攊ncreases your risk for EO-CRC, while the data on smoking is听(although smoking is really bad for your overall health, so that鈥檚 no reason to pick up a cancer stick today).
Because EO-CRC is a birth cohort phenomenon, researchers have picked their brains to list every change that has happened to society in the last decades, including a rise in C-sections and bottle feeding. Could it be our increasingly sedentary behaviour? Possibly. Could it be a more liberal use of antibiotics, especially in children and adolescents? They do alter our gut microbiome and they听听in the development of colorectal cancer overall. Vitamin D deficiencies? A perennial boogeyman, but the evidence here is听.
Our diet? That鈥檚 the potential risk factor I have seen flagged most often. The last half a century has seen an increased availability of red and processed meat, a higher consumption of refined grains, as well as an explosion in food products with added sugar. And dietary fibres? Many of us don鈥檛 get enough of them in our diet. Is this the key to understanding EO-CRC? There is likely no single cause, but diet is bound to play a role, although even here it鈥檚 hazy. You would think that fibre from fruits and vegetables would help ward off the cancer, but the evidence right now is听听and听.
This ambivalence is unsatisfying, which is why health influencers are likely to latch onto any aspect of modernity and unflinchingly declare it听ingrediens non gratum.听Food dyes, artificial sweeteners鈥攂asically anything consumed by mouth that doesn鈥檛 sound 鈥渘atural鈥� will be labelled dangerous by people who either do not read or do not understand the scientific literature. The goal is to find something to blame now instead of waiting for scientists to figure it out.
Scientific research is painfully slow. Studies must be designed and sold to whoever holds a purse鈥檚 strings. They must then unfold, often over the course of years, and their data must be analyzed before the whole thing is written up as a paper to be shopped around until, a year or two or three later, it gets published. Moreover,听every study is flawed.听None is perfect. A study looking at听, for example, may find a connection鈥� but what if it鈥檚 the disease for which the steroids were prescribed that puts you at risk for cancer, and not the steroids themselves? An observational study will not be able to adjudicate. A growing body of evidence is thus flawed in multiple ways. Clarity emerges eventually from one study compensating for another鈥檚 flaws and vice versa, and from larger, better (and more expensive) experiments.
Studying cancer is also challenging because it takes decades for the disease to manifest. You can study mice instead, animals with a shorter life span, but we are not giant rodents, so results do not always translate.
Frustrating, isn鈥檛 it?
Screening everyone is not the solution
Our gut reaction when it comes to cancer is to test everyone as often as possible. After all, if you screen everyone, you should find all of the cancers, right? Hence the public鈥檚 appetite for full-body MRI scans and direct-to-consumer kits that promise to test your entire genome for anything that might be wrong with you now and in the future.
But counter to our intuition, cancer screening needs to be smart, not all-inclusive. Screening costs money and resources, and healthcare systems (especially public ones) do not have infinite pockets. Importantly, screening tests are imperfect. They will find things that are not cancer but that will appear like they could be, what doctors cheekily refer to as incidentalomas. This leads to anxiety and to more invasive testing, like biopsies, which uses up resources.
The age at which to begin colorectal cancer screening in the United States was decreased from 50 to 45 in the last few years because of this rise in early-onset colorectal cancer. In Canada, the recommended age remains 50. There are valid arguments听against听screening younger people for this cancer. Yes, rates are going up, but in terms of absolute numbers, the increase is听. To call it an 鈥渆pidemic鈥� strikes me as an overstatement. If you鈥檙e in your twenties, the risk that you will be diagnosed with colorectal cancer in the next five years is听听than your risk of being in a motor vehicle accident or of accidental poisoning.
Also, about听听of all patients with EO-CRC get their diagnosis before the age of 45, so lowering the age limit for screening in Canada to 45 would only help half of these people. To lower it even more would gobble up resources by screening a large number of people who do not have cancer, which may affect older adults鈥� ability to get checked, and they are the ones most likely to benefit from it鈥攁gain, nine out of 10 cases of colorectal cancer are seen in people over the age of 50.
And screening is not the panacea we may think it is. Only听听moderately sized colon polyps鈥攇rowths in the colon that are usually benign and that can be found and removed during a scoping procedure鈥攊s expected to progress to an invasive cancer. Finally, even though the U.S. lowered their screening age to 45, their task force in charge of evaluating evidence for primary care and health prevention estimated that this change would actually only prevent听听per year. No one should die from cancer; but when managing limited resources (doctors, nurses, laboratory personnel), all of these considerations must be tallied up.
So, yes, we are seeing a rise in adults being diagnosed with colorectal cancer before the age of 50. It is a noticeable uptick, and a worrying one, but it is not a sea change either. And the causes for this increase remain unclear, though they are likely to be tied to how society has changed in these last fifty years, especially to the kind of food we eat.
What can we do about it? Exercising regularly, lowering our meat consumption, restricting our alcohol and added sugar intake, and getting听听(25 grams a day for women, 38 for men) are all defensible pieces of advice, even if the data on their protective effect for colorectal cancer specifically is not always consistent. And keeping an eye out for evolving public health recommendations is important, too.
Beware of influencers jumping on a study in mice to tell you what not to eat. They鈥檙e full of鈥� well, enough about the colon for today.
Take-home message:
- The number of people over the age of 50 being diagnosed with colorectal cancer every year has been going down, but this same number for people below the age of 50 has steadily increased.
- A number of possible reasons have been put forward鈥攃hanges in our diet, sedentary behaviour, obesity, even increased use of antibiotics in younger people鈥攂ut the overall scientific evidence remains ambiguous, and this increase is likely due to multiple changes in our habits.
