basics – Precision Digestive Care

Cologuard® vs. Colonoscopy: Which test is better?

Posted on September 24, 2023 - 1:25 pm by Frederick Gandolfo MD

In the US, colorectal cancer is currently the second leading cause of cancer deaths in men and women combined. Virtually all health professionals agree that screening average-risk people starting at age 45 for colorectal cancer is the best way to prevent this disease. There are a few highly effective tools available for colorectal cancer screening: This article will focus on the two most popular tests, colonoscopy and the Cologuard test.

Most people are familiar with colonoscopy, but in case you’re not…colonoscopy is a safe 15-20 minute outpatient procedure that is done using sedation (so it’s painless) that entails using a flexible scope inserted in the rectum (the end part of the colon) and carefully advanced to the cecum (the other end of the colon) to inspect the entire colon lining for the presence of polyps, tumors, and other abnormalities. A polyp is a “precancerous” growth that is common and if not removed can slowly grow and eventually may turn into colon cancer. During a colonoscopy, the doctor can both find polyps and remove these polyps at the same time. Therefore colonoscopy can both diagnose cancer and polyps, but more importantly colonoscopy can prevent colorectal cancer from occurring in the first place by removing precancerous polyps years before they would have otherwise become cancer. A normal colonoscopy typically does not need to be repeated for 10 years. If polyps are found and removed, a colonoscopy will be recommended sooner, to make sure any new polyps that grow will be found and removed before having a chance to turn into colon cancer. Colonoscopy is considered the gold-standard colon cancer prevention test and is the preferred test by most medical societies.

Image of colonoscopy with polyp removal. — Removing a precancerous polyp with colonoscopy.

Cologuard® is a non-invasive, commercially-available screening test for colorectal cancer. The test is ordered by a doctor (typically a primary care provider) and mailed to the patient’s house. When the urge to have a bowel movement strikes, the patient places the Cologuard collection device over the toilet and makes a deposit. There are a few simple preparation steps such as adding in a small amount of liquid that the company provides, and then the entire container of poop is mailed back to the company in the provided packaging. The Cologuard test looks for blood and certain DNA mutations in the stool to determine if a test is positive or negative. A week or so later the doctor gets a report indicating the result. If the test is negative, it only “protects” the patient for 3 years.

So which test is better, colonoscopy or Cologuard?

Well, it really depends on what the goals are…

As a general philosophy, it’s much more effective to prevent a disease from occurring rather than waiting for the disease to occur, then reacting to it. When the disease in question is colon cancer, preventing it starts with healthy diet and lifestyle as well as screening the population at large for polyps, the precancerous growths that cause colon cancer. To have a colonoscopy and remove a significant polyp is akin to stopping a future cancer from occurring in the first place. When effective preventive tests like colonoscopy exist, to wait until a patient has developed cancer and then treating the cancer is like waiting until you have been in a car accident to then put on your seatbelt…it’s too late. Although there are excellent treatments available for colorectal cancer nowadays, including surgery and chemotherapy, treating cancer is not the goal of screening. The goal of screening is to not develop cancer of the colon in the first place!

Typically, when an effective prevention technique exists (like removing precancerous polyps during colonoscopy) the earlier we can screen for colon cancer the better. This is why colonoscopy is the preferred test for younger healthier people starting at age 45. Save a 45-50 year old from colon cancer and you will potentially give that person 30-40+ years of life having not developed colon cancer. Saving a 79 year old from colon cancer is still a commendable goal, however the average 79 year old typically won’t have as many quality years left “in the tank” compared to the average 45 year old.

So why does this philosophical stuff matter when it comes to picking a colorectal screening test? Well, understanding what these tests do helps you understand how to apply the proper test to your individual goal.

If this article is already too long and you just want the bottom line, here it is: Colonoscopy is the superior test for most people, especially “younger” people (age 45-mid 70s). It can both detect and (more importantly) prevent colorectal cancer. It is semi-invasive and less convenient when compared to Cologuard testing. Cologuard is an easier test but plagued by false negatives and false positives. Cologuard does not necessarily prevent cancer, it only detects cancer after cancer has occurred, or at best detects large polyps that are close to becoming cancer. Cologuard should be considered for older patients (age 75+), for patients that may not have the best overall health, or for patients who have specific reasons why they cannot have a colonoscopy.

OK, you asked for it! Here are more details, starting with the Cologuard test:

The study that determined the characteristics of the Cologuard test basically performed the test on almost 10,000 patients at average-risk of colon cancer, and then had the patients undergo colonoscopy as the gold-standard test. The results of the Cologuard test were not available to the patients or the endoscopist at the time of the colonoscopy. The major results of this study showed that the Cologuard test had a sensitivity (the amount of times it picked up colorectal cancer when cancer was indeed present) of 92%. It was far less sensitive for picking up advanced precancerous polyps, at only 42%. It turns out that sensitivity is the main thing we care about in a screening test: we want the test to miss none of the patients who have the disease. A perfect screening test would have a sensitivity of 100%, meaning that if 100 people have colon cancer and have the test, all 100 people will get a “positive” test result, meaning no false negative tests.

Sensitivity isn’t everything however…we also want a test that gives a negative result when someone does not have the disease in question. That is, if you take a group of 100 people that do not have colorectal cancer, a perfectly specific test will have 100 “negative” results, meaning no false positive tests.

What does a positive Cologuard test mean?

First and foremost, a positive result on the Cologuard test means that you need to have a colonoscopy. Not a virtual colonoscopy, or another stool test, or another scan of some sort…you need a real optical colonoscopy. Luckily, only about 4% of people with a positive Cologuard test will have cancer found on colonoscopy. 51% will have a precancerous polyp. The rest (45%) will have nothing found on colonoscopy. So to simplify even further, just a little more than half of people with positive results will have something abnormal (cancer or a polyp) found on colonoscopy.

What does a negative Cologuard test mean?

A negative test means that there is a less than one-percent chance of having cancer found on colonoscopy. However, about 34% of people with negative tests still have precancerous polyps found on colonoscopy, with the remainder (66%) of people with negative Cologuard results having truly negative colonoscopies.

What is immediately apparent from these numbers is that Cologuard rarely misses cancer. However, if we count polyps as a significant finding, there are plenty of false-positive results (45%) and plenty of false-negatives too (34%).

A word on how health insurance companies view Cologuard…

While not important to the medical reasoning behind choosing colonoscopy or Cologuard, for some people it is important to note the finances of each test. Either colonoscopy or Cologuard can be considered a screening test, and is typically covered by health insurance plans without an out-of-pocket cost. However, if a Cologuard test is positive (remember that 45% false positive rate discussed above), the insurance company now views the necessary colonoscopy as a diagnostic colonoscopy, not a screening colonoscopy. Diagnostic tests often have an out-of-pocket responsibility for the patient and in the case of a colonoscopy this can be in the thousands of dollars range. This is something rarely discussed when ordering a Cologuard test in the primary care setting, but that we often need to educate patients about when it’s time to book their colonoscopy to follow up a positive Cologuard test.

What about colonoscopy? Are there any downsides?

In good hands, colonoscopy is an excellent test—it’s the best test we have in the fight against colon cancer. However, no test is perfect and colonoscopy is no exception. Even though colonoscopy is the gold-standard test, here are some of the negative things to know about colonoscopy.

Colonoscopy requires a bowel preparation, meaning you have to take either a liquid prep or pill prep to clean out the colon the day before. It’s not painful, but prepping for a colonoscopy is far from a good time. Colonoscopy has small but real risks, such as bleeding, infection, perforation of the bowel, and anesthesia problems. However these risks are very rare, and in with a skilled team the risk of a serious complication is far less than 1 in 1,000 procedures. Colonoscopy also has a miss rate for polyps and even cancer. It is very hard to define an actual number of missed lesions because it’s difficult to perform a study on the gold-standard test (colonoscopy) as there is no better test to compare it to. That being said, colonoscopy can miss small polyps around 20% of the time, and can even miss cancer a few percent of the time. The devil is in the details however: Missing a significant lesion during an outpatient screening colonoscopy in a properly prepped patient (meaning the patient did the bowel cleanse effectively) with a doctor that performs high-quality colonoscopy (meaning the doctor spends adequate time and uses excellent technique to find and remove polyps) is quite a rare event and is something that is difficult to study given variations in quality practice between doctors even in the same community or hospital system.

Here is a quick pros and cons table to help clarify all of the above

Measure	Colonoscopy	Cologuard®
Prevention of colon cancer?	Yes	Not really
Repeat a normal test every	10 years	3 years
Overall convenience	Bowel prep and 1 day off work	No prep but have to handle stool
Overall invasiveness	Moderately invasive	Not invasive
Accuracy	Very accurate	Not very accurate
Biggest upside of the test	Better cancer prevention and accuracy	Easy and can do it at home
Biggest downside of the test	Bowel prep and less than 0.1% chance of complications	Lots of false positives that will require a colonoscopy anyway

How do I choose between colonoscopy and Cologuard in my practice?

I typically reserve Cologuard testing for patients that just need to know if they have cancer right now, and are not in good condition to undergo colonoscopy due to other major health issues. A patient that has not been screened recently who is approaching 80 years old, and who has one or more major cardiovascular or pulmonary issues is a good candidate for Cologuard testing. For pretty much everyone else, colonoscopy is by far the better test.

References:

Imperiale TF, Ransohoff DF, Itzkowitz SH, et al. Multitarget stool DNA testing for colorectal-cancer screening. N Engl J Med 2014;370:1287-97.

Cologuard website: http://www.cologuardtest.com/current-patients/how-to-use

Cologuard is a registered trademark of Exact Sciences Corporation.

Everyone should know these key facts about colorectal cancer

Posted on March 15, 2019 - 1:55 am by Frederick Gandolfo MD

March is Colorectal Cancer Awareness Month, so I made this infographic to highlight the key facts that everyone should know about colorectal cancer!

For much more about this and other important health topics, please visit my informational site Retroflexions.com!

March is Colorectal Cancer Awareness Month

Posted on March 1, 2018 - 3:23 pm by Frederick Gandolfo MD

It’s March, which means it’s Colorectal Cancer Awareness Month!

Preventing colon cancer is one of the most important things that we gastroenterologists get to do. Even if you’re not particularly interested in colon cancer, there will still be some interesting stuff for you to read this here as I will cover a little bit about nutrition, exercise, and healthy lifestyle choices as they relate to colon cancer prevention. I also look forward to sharing a somewhat humorous and true story about bowel prep from the perspective of a patient, and that patient is me!

First, I’d like to review some basic facts about colorectal cancer for any new readers out there:

What is colorectal cancer?

Cancer, in general, is when your own cells develop DNA mutations and eventually stop obeying the normal control signals from the body that function to tell the cells when to stop dividing and where not to grow (obviously this is a gross oversimplification). These rebellious cancer cells multiply and form a tumor, which is just a mass of cancerous cells. Tumors can grow into other organs and cause damage, blockages, bleeding, and other types of badness. The cells inside the tumor can also spread through the bloodstream or lymphatic system and land in other locations in the body, a process known as metastasis.

Colorectal cancer is when this process happens in the colon (or the rectum, which is the end portion of the colon). The cells that transform into the typical type of colon cancer originate from the inner lining of the colon and turn into a type of cancer called adenocarcinoma.

How does colorectal cancer happen?

Colorectal cancer occurs when a precancerous polyp (known as an adenoma) forms inside the colon and slowly accumulates additional genetic mutations, causing the polyp to grow larger and act more aggressively, eventually invading into the muscle layer of the colon wall and becoming full-blown cancer. We think this process takes about 10-20 years to occur, which is a very important fact when it comes to colorectal cancer prevention. This long sequence, from adenoma to cancer, is the reason why screening can prevent colon cancer—we can intervene during the long precancerous stage and change the natural history of the disease. Stated more simply, we can remove the precancerous polyp before it actually turns into colon cancer, therefore preventing colon cancer from developing at all!

How do we prevent colon cancer?

All professional gastrointestinal societies recommend starting to screen most people for colorectal cancer starting at fifty years old. However, true prevention really starts many years before most people have to worry about getting a colonoscopy! Diet, exercise, and many lifestyle choices can increase or decrease the risk of developing colorectal cancer. We will cover this important topic in more detail later this month.

As far as screening goes, there are various tests available to look for both colorectal cancer and adenomatous polyps. I have covered these topics in more detail in past articles, so I will invite new readers to peruse the links below for more info:

However, if you are in a hurry and don’t want to read those older articles, we can boil down the testing recommendations for most individuals as follows: To prevent colorectal cancer, the average-risk man or woman should have a colonoscopy starting at age 50, and then every 10 years thereafter, until about 75-85 years of age. If polyps are found, they are removed during the colonoscopy, and the next exam is scheduled sooner than 10 years later.

colon cancer awareness

Can young people get colon cancer?

Most cases of colon cancer are diagnosed in people in their late sixties and early seventies, with rectal cancer being diagnosed somewhat earlier (early sixties). The good news is that colorectal cancer rates in the over-fifty population are on the decline! This may be due to several factors such as the increase in effective colorectal cancer screening programs and a decline in the popularity of smoking. However, new data is showing that the rate of colorectal cancer in young people is actually on the rise! Although it is still relatively rare, the rate of colorectal cancer is increasing in the 30- and 40-year-old age group.

We are not quite sure why colorectal cancer is increasingly developing in the younger population. Various theories exist, including the influence of obesity, inactivity, food additives, poor diet, and even antibiotic exposure. All we can conclude at this point in time is that symptoms that could be consistent with colorectal cancer should not be ignored just because a patient is relatively young.

Well, that about wraps up the basics on colorectal cancer. I am going to hit this topic from all angles this month, so be sure to keep reading!

For a quick reference on colorectal cancer, see the American Cancer Society’s publication Colorectal cancer facts and figures 2017-2019.

Can you eat seeds, nuts, and popcorn if you have diverticulosis? Can diet prevent diverticulitis?

Posted on October 24, 2017 - 4:09 pm by Frederick Gandolfo MD

Diverticulitis is a common and sometimes serious problem that affects several hundred thousand people each year. Diverticulitis is the condition where small outpouchings or “pockets” in the wall of the large intestine called diverticula become inflamed and infected, and typically presents as a constant lower abdominal pain, associated with fever or chills, and often bloating or constipation symptoms. Despite becoming even more common in recent years, not much is understood about why diverticulitis occurs.

Diet has long been implicated in the formation of these diverticula which can eventually become inflamed leading to diverticulitis (the condition of just having the pockets without an associated infection/inflammation is called diverticulosis). We know that diverticular disease is rare in countries where fiber intake is high, and we know that when populations change to a more westernized diet (poor in fiber/rich in protein, fat and processed sugars) the rate of diverticular disease rises accordingly. So if fiber is protective against developing diverticular disease in the first place, does it stand to reason that supplementing fiber when one already has diverticulosis will help prevent future complications?

The answer to the above question is unknown, but because fiber is a mostly harmless supplement and has other health benefits, we often recommend fiber supplementation to patients after they are diagnosed with diverticulosis or diverticulitis. But what about the common advice of avoiding seeds, nuts, corn, and popcorn that is readily doled out by some doctors and most family members/friends as soon as they hear the words diverticulosis or diverticulitis? One can reason that it makes common sense to try to avoid having sharp, hard, indigestible seeds getting stuck in a diverticulum and causing an abrasion or perforation which may lead to infection and other nastiness. But does this recommendation have any valid scientific reasoning behind it?

While I’m not sure when or where this recommendation started, it probably belongs more under the category of “old wives’ tale” rather than scientific fact. Let me explain my reasoning for this:

It is very commonly observed during colonoscopy that patients with diverticulosis are found to have a small ball of stool impacted in each and every diverticulum. Presumably, this is the natural state of affairs in the colon of the patient with diverticulosis. So if small hard pellets of stool (mostly composed of indigestible waste and bacterial mass) do not cause an infection, why would a small seed or nut cause a problem? Nevertheless, people still take great pains to avoid seeds, nuts, and corn, causing themselves a fair amount of grief when it comes to meal options. Is this all worth it?

I would reason that it is not necessary to avoid seed and nuts if you have diverticular disease. Probably the best evidence we have that seeds, nuts, corn, and popcorn do not cause complications in patients with diverticular disease comes from a study published in JAMA in 2008 showing that not only was intake of nuts, seeds, popcorn, and corn NOT associated with developing diverticulitis, but in fact the opposite was true. Eating more seeds, nuts, corn, and popcorn actually seemed to be associated with LESS of a chance of developing diverticulitis! These foods are thought to be somewhat anti-inflammatory, and therefore may protect against diverticulitis.

So what is the ideal diet to prevent development of diverticular disease? I think it is pretty obvious that a high-fiber diet is king in preventing the development of diverticulosis. But what if you are late to the high-fiber party but still want to make some changes to prevent that next attack of diverticulitis? Starting a high-fiber diet later in life may still help to reduce the progression of more diverticula, but unfortunately there is no way to reverse the existing diverticula (besides surgical resection of the diseased segment of colon). However, there are still diet changes you can make that might help.

It seems that diets high in red meat are also associated with the development of diverticulitis. This is independent of the effect of fiber, as red-meat eaters develop diverticulitis more often than their vegetarian counterparts even after controlling for fiber intake between the groups. What is more interesting is that researchers found that the recent diet for the past 1-4 years before developing diverticulitis seemed to shape the risk more than the lifelong diet habits. That means that changing to a high-fiber, low-red-meat diet now can still lessen your chance of developing diverticulitis in the near future. But look at the bright side–at least you can eat all the seeds, nuts, corn, and popcorn you want!