Colon cancer screening
Shouldn’t screening look for more than cancer?
Finding cancer matters. Finding and removing precancer creates an opportunity to prevent it.
Written by Stephen Rudolph, MD, a practicing gastroenterologist. Self-funded, with no money from any test maker.
A small polyp is about this size. You would never feel it. Left in place, a polyp can grow into cancer, quietly, over years. Colonoscopy can find it and remove it in the same visit.
1Why colonoscopy first
How well does your test find precancer?
Among 100 people who already had advanced precancer, one round of Cologuard Plus found this many:1
- 43
- detected by the stool test
- 57
- not detected by the stool test
Colonoscopy can find precancer and remove it.
It looks at the whole colon directly. When a polyp is found, it can usually be taken out during the same exam. A polyp that has been removed can’t turn into cancer.
The change from polyp to cancer usually takes years. That is the window.
A note from the doctor
“My colleagues and I were diagnosing colorectal cancer and advanced precancer in younger adults. I grew concerned that people choosing a screening test didn’t always have a clear picture of how the tests differ in finding precancer, and in removing it. This site is that picture.”
If a colonoscopy isn’t right for you, a different screening test is far better than none. I only ask that you choose knowing what each one can and cannot do.
Stephen Rudolph, MD
Gastroenterologist, Minnesota. I pay for this site myself, with no outside funding. I am an owner of a gastroenterology practice and its endoscopy centers, and I earn income from clinical care, including colonoscopy. You should know that. Funding & disclosures
2Compare the tests
Both recommended. Not the same job.
If a stool test is what gets you screened, do it. Here is what differs, and what to know about your result.
| What matters | Colonoscopy | Cologuard Plus (stool DNA) | FIT (stool blood) |
|---|---|---|---|
| Finds cancer that is already there | Yes, by looking directly | About 94 of 100 | About 67 of 100 |
| Finds advanced precancer | Yes, by looking directly. It can still miss some. | About 43 of 100 | About 23 of 100 |
| Removes polyps | Yes, usually during the same exam | No | No |
| What it asks of you | A prep, sedation and a ride home | A kit at home. No prep. | A kit at home. No prep. |
| How often, if normal | Usually every 10 years | Every 3 years | Every year |
| If something is found | Removed or sampled during the exam | You need a colonoscopy to finish | You need a colonoscopy to finish |
| What a normal result means | No polyps were seen. Small ones can be missed. | Cancer is very unlikely. About 1 in 15 still had advanced precancer. | Cancer is unlikely. One test misses most advanced precancer. |
Detection figures come from one screening round in the BLUE-C study (2024), which checked both stool tests against colonoscopy. “1 in 15” is from the FDA review of Cologuard Plus. Testing intervals follow current screening guidelines.
The full test-by-test comparisonIf both are recommended, are they equivalent?
3What it’s actually like
Nobody calls the prep fun. Here’s the rest of the truth.
Does it hurt?
Most people are sedated and comfortable, and many remember little of it. Some bloating or cramping afterward is common.
Comfort and visit timeHow bad is the prep?
It’s the part people dread: an evening and a morning near a bathroom. A clean colon is what lets your doctor see small polyps.
What to expect from the prepWhat will it cost?
It depends on your plan and on why the exam is done. Before the day, ask your insurer and the procedure team about the doctor, facility, anesthesia and lab fees.
Coverage questions to askHow much time will I need?
Plan to take the procedure day off if you’re sedated, and arrange a ride home. The exam itself usually takes less than an hour.
Planning the dayWhat if they find something?
Many polyps are removed during the exam and sent to a lab. A polyp does not automatically mean cancer. Ask how you’ll get the result and what comes next.
Polyp results and follow-upWhat are the real risks?
About 3 perforations and 15 major bleeds for every 10,000 screening exams. We give you the numbers, not just the word “rare.”
The limits, with the source4See if you’re due
Feeling well isn’t the same as being in the clear.
Polyps and early colon cancer usually cause no symptoms. Screening is for people who feel fine, and for most adults it starts at 45. Four questions tell you where you stand.
Evidence & studies
Every number has a denominator.
For each study we say what it measured, what it did not, and who paid for it. That includes the studies that cut against us.
- After polyps were removed, 53% fewer colorectal cancer deaths than expectedNational Polyp Study, 2012. Nearly 16 years of follow-up.For colonoscopy
- Fewer cancers in the group invited to colonoscopyNordICC randomized trial, 13-year results. Only 42% of those invited attended.For colonoscopy
- Cologuard Plus found 43 of 100 advanced precancersBLUE-C, 2024. Funded by the manufacturer.About stool tests
- A repeated FIT program matched colonoscopy on cancer deaths at 10 yearsCOLONPREV randomized trial. It tested FIT, not Cologuard.The case against us
More in the library
- Start at 45Why screening now begins in your 40s
- A high-quality colonoscopyHow to choose your doctor and get a careful exam
- Preparing for your colonoscopyThe prep, the day itself and recovery
- All patient questionsTime off, cost, results and more
- Patient resourcesPrintable guides and questions to ask
- How to arrange your colonoscopyWho to call and what to say
Posters & short films
Serious message. Not a serious tone.
-
The Eviction CallShort film, 0:53 -
The Hype ManShort film, 1:09 -
The Wildlife SpecialistShort film, 2:07
Three short films. A polyp gets an eviction notice.
A hype man starts asking questions. A wildlife specialist can find the raccoon but won’t remove it. Each is a fictional, AI-created scene with captions. Pick any film or poster to see it full size.
Dad’s Camping Trip
Dad’s Rental Car
Dad’s Grill
All boats take on a little water.
It’s going around us.
You’re paying for the name.
The Barber
The Home Inspector
The Wedding Fitting
Before Cancer
Both Recommended. Not Equivalent.
94% of What?