# Colon Cancer Symptoms: Warning Signs and When to Get Checked

Source: https://jilllebofsky.com/colon-cancer-symptoms/
By Claire Hadley, Reviews Editor. Updated November 9, 2026. Facts checked November 9, 2026.

**Quick answer:** The main colon cancer symptoms are blood in or on the stool, a bowel change that lasts more than a few days, belly cramps or bloating, unexplained weight loss and fatigue from anemia. Early cancer often causes no symptoms at all. Any rectal bleeding deserves a doctor visit, and a colonoscopy, not a blood test, is the usual first step when you have symptoms.

Colon cancer symptoms often start small: some blood in the stool, a bowel habit that changes and stays changed, or tiredness from slow blood loss[1]. We read the National Cancer Institute (NCI) patient guide, the American Cancer Society (ACS) symptom and statistics pages, NCI SEER survival data, a 2023 study of 5,075 younger patients and the FDA record for the first blood test approved for screening.
The short answer: rectal bleeding, or a bowel change that lasts more than a few days, deserves a doctor visit[3]. Cancer found while still local has a 91.3% five-year survival rate[5].
Colon cancer at a glance
What it isCancer that starts in the colon, part of the large intestine; about 108,860 new colon cases are expected in the US in 2026[4]
Most common symptomsBlood in the stool, a change in bowel habits, belly discomfort, weight loss and fatigue[1]
Early stageOften no symptoms, especially at first[2]
Who gets itMedian age at diagnosis is 66; rates under 50 rose 2.9% a year from 2013 to 2022[5][4]
How it is foundStool tests, colonoscopy and a biopsy; blood tests help but cannot diagnose it alone[1][11]
Outlook91.3% five-year survival when local, 16.9% when it has spread to distant organs[5]
When to actAny rectal bleeding, or a bowel change lasting more than a few days[2][3]

Colon cancer by the numbers. Sources: NCI SEER, American Cancer Society, JNCI 2023 (Fritz et al.), NIDDK, USPSTF.
What are the most common colon cancer symptoms?
The most common colon cancer symptoms are blood in or on the stool and a change in bowel habits that does not go away. NCI also lists belly discomfort, narrower stools, a feeling that the bowel does not empty, weight loss with no known reason and fatigue[1]. Many people notice only one or two.

Blood in the stool that is bright red or very dark[1]
Diarrhea, constipation or narrow stools that last more than a few days[2][3]
A feeling that you need a bowel movement that is not relieved by having one[3]
Gas pains, bloating, fullness or cramps in the belly[1]
Weight loss you cannot explain[1]
Feeling very tired or weak[1]
Vomiting[1]

Bleeding from the lower bowel can show up as stool coated with bright red blood, dark blood mixed into the stool, or black, tarry stool[9]. ACS notes that the stool often looks normal even when there is some bleeding[3].
How long a change lasts matters more than the change itself. A day of loose stool after a meal out is common, while MedlinePlus flags a change that lasts more than a few days[2].
What are the early signs of colon cancer?
Early colon cancer often causes no signs at all, which is why screening exists. MedlinePlus says colorectal cancer may not cause symptoms, especially at first[2]. ACS adds that most people with polyps, the small growths screening looks for, have no symptoms[3]. When early signs do appear, slow bleeding is a common one.
According to ACS, the first sign is sometimes a blood test that shows a low red blood cell count[3]. That happens because a tumor can bleed a little at a time, too little to see.
Over weeks, that blood loss can lead to iron-deficiency anemia. The National Heart, Lung, and Blood Institute (NHLBI) lists colon cancer among the causes of bleeding that lead to it[10]. Its symptoms include:

Tiredness and weakness[10]
Dizziness[10]
Cold hands and feet[10]
Pale skin[10]
Shortness of breath[10]

Doctors confirm anemia with a complete blood count and iron tests such as ferritin[10]. If a blood count shows iron-deficiency anemia and nobody has found the reason, ask your doctor whether your bowel should be checked.
Is it colon cancer, hemorrhoids or IBS?
Symptoms alone cannot tell colon cancer apart from hemorrhoids or irritable bowel syndrome (IBS). ACS says these same symptoms are often caused by infection, hemorrhoids or IBS, yet it still advises seeing a doctor right away so the cause can be found[3]. NIDDK says rectal bleeding can be a sign of colon cancer[8].
Hemorrhoids and colon cancer: how the signs overlap
SignHemorrhoidsColon cancer

BloodBright red, on the stool, toilet paper or in the bowl[8]Bright red or very dark[1]
PainInternal hemorrhoids are most often not painful[8]Gas pains, bloating or cramps[1]
Next stepSee a doctor for rectal bleeding, or if symptoms last after 1 week of home care[8]See a doctor right away[3]

Because both can cause bright red blood, you cannot judge the source at home. MedlinePlus lists hemorrhoids, polyps and colon cancer among the causes of bleeding in the digestive tract[9].
IBS causes cramps, bloating and bouts of diarrhea or constipation, which is why it gets confused with bowel cancer. Our guide to IBS symptoms walks through that pattern. A new fiber routine can also change stools for a while, as our psyllium husk guide explains, but a supplement does not explain blood in the stool.
Can colon cancer symptoms show up before age 50?
Yes. Colon cancer is rising in adults under 50, and the symptoms are easy to brush off. ACS reports that rates in this age group rose 2.9% per year from 2013 to 2022[4]. NCI notes that far less than 1% of younger adults get it[7], so most symptoms turn out to be something else.
A 2023 study in the Journal of the National Cancer Institute looked at 5,075 people diagnosed before age 50[6]. Four red-flag symptoms stood out: belly pain, rectal bleeding, diarrhea and iron-deficiency anemia. Each raised the odds, with odds ratios from 1.34 to 5.13[6].
The risk climbed as the symptoms stacked up. One symptom was linked to 1.94 times the risk, two to 3.59 times and three or more to 6.52 times[6].
Many of those patients waited a long time. In that study, 19.3% of patients had their first red-flag symptom between 3 months and 2 years before diagnosis, a median gap of 8.7 months[6]. NCI says only 10% to 20% of early-onset cases come from inherited factors[7], so a clean family history does not rule it out.
What are the signs that colon cancer has spread?
When colon cancer spreads, the new symptoms depend on where it goes. ACS lists an enlarged liver felt during an exam, yellow skin or eyes (jaundice) and trouble breathing as possible signs of spread[3]. SEER data show 23% of cases are found after the cancer has reached distant organs[5].
Stage at diagnosis is the biggest factor in the outlook. The SEER numbers below cover people diagnosed from 2016 to 2022[5].
Colorectal cancer stage at diagnosis and five-year relative survival (SEER)
Stage when foundShare of casesFive-year survival

Localized (still in the colon or rectum)34%91.3%
Regional (nearby lymph nodes or tissue)37%75.2%
Distant (other organs)23%16.9%
All stages100%65.4%

The gap between 91.3% and 16.9% is the reason doctors push people to report symptoms early[5]. SEER estimates 158,850 new colorectal cancer cases in 2026[5], and ACS expects about 55,230 colorectal cancer deaths in the US in 2026[4].
Is there a blood test for colon cancer?
Yes. In July 2024 the FDA approved Shield, a blood test that screens adults 45 and older at average risk. The FDA says it detects colorectal cancer 83% of the time, and about 1 in 10 people without advanced abnormal cells gets a false positive[12]. It does not replace a diagnostic colonoscopy.
The FDA record adds three limits. The test is not for people at high risk, a negative result does not guarantee you are cancer free, and a positive one needs a colonoscopy[12]. It needs up to four tubes of blood and no bowel prep[12].
Routine blood tests play a different role. A complete blood count can show anemia, and a CEA test can be raised, but ACS says CEA cannot be used alone to screen for or diagnose cancer[11]. NCI notes that normal cells release CEA too[1].
What the studies found
Key studies on colon cancer symptoms and detection
StudyWho and how manyWhat it measuredResult

Fritz et al., JNCI 20235,075 people diagnosed before 50Red-flag symptoms before diagnosisThree or more symptoms: 6.52 times the risk[6]
ECLIPSE, NEJM 2024 (funded by Guardant Health, the test maker)7,861 average-risk adultsShield blood test against colonoscopyFound 83.1% of cancers and 13.2% of advanced precancerous lesions; specificity 89.6%[13]
NCI SEER registryUS cases, 2016 to 2022Five-year survival by stage91.3% local versus 16.9% distant[5]

The ECLIPSE figure for early cancers, stage I to III, was 87.5%[13]. Polyps are where it falls short: catching 13.2% of advanced precancerous lesions means the test misses most of the growths that colonoscopy can find and remove. ECLIPSE was paid for by the company that makes the test, so treat it as one industry study.
How do doctors diagnose colon cancer?
Colonoscopy is the main test doctors use to find the cause of bleeding or a bowel change. NIDDK says doctors use it to look for the cause of bleeding, changes in bowel habits, belly pain and weight loss, and that it usually takes less than one hour[14]. A biopsy taken during the test confirms cancer[1].
The usual workup runs in this order:

A health history and physical exam, often with a digital rectal exam[1].
Blood tests: a complete blood count for anemia and liver enzyme tests[11].
A stool test for hidden blood, such as a fecal immunochemical test (FIT)[1].
Colonoscopy, with a biopsy of anything that looks abnormal[1][14].
Imaging such as virtual colonoscopy when needed[1].

Colonoscopy is safe but not risk free. NIDDK puts perforation at about 3 and bleeding at about 15 in every 10,000 procedures[14].
How colon cancer is treated
NCI says surgery is the most common treatment for all stages of colon cancer[1]. Cancer inside a polyp is often removed during the colonoscopy itself.
Larger tumors need a partial colectomy, where the surgeon removes the cancer and joins the healthy ends. Advanced cancer may add chemotherapy, targeted therapy or radiation[1]. No supplement replaces any of these, and our gut health supplements guide keeps to what probiotics and fiber products were actually studied for.
Screening if you have no symptoms
The US Preventive Services Task Force (USPSTF) advises screening from 45 to 75, and selectively from 76 to 85[15]. Its advice covers adults who do not have signs or symptoms. If you do have symptoms, your doctor will order a diagnostic workup, usually starting with colonoscopy, instead of a screening test. Screening also has a second job: a colonoscopy can find and remove polyps before they have a chance to grow[14].
USPSTF screening options and how often
TestHow often

FIT stool testEvery year[15]
Stool DNA-FITEvery 1 to 3 years[15]
CT colonography or flexible sigmoidoscopyEvery 5 years[15]
ColonoscopyEvery 10 years[15]

When should you see a doctor right away?
See a doctor promptly for any rectal bleeding or a bowel change that lasts more than a few days, and get emergency care for heavy bleeding or signs of shock. ACS advises seeing a doctor right away about these symptoms[3]. NIDDK calls shock from bleeding life-threatening[16].
The lists below sort the signs by how fast to act. They come from NIDDK guidance on digestive bleeding and the ACS symptom page, and they are a guide for when to get help, never a way to diagnose yourself.
Call 911 or go to the emergency room if

You pass black, tarry stool or a lot of blood and feel faint, dizzy or lightheaded[16]
You vomit blood, or vomit that looks like coffee grounds[16]
You have signs of shock: confusion, a fast heart rate, pale skin, cold hands and feet, or sweating[16]
You are short of breath along with bleeding[16]

NIDDK notes that acute bleeding begins suddenly and can be severe, so do not wait to see whether it stops[16]. Slow, chronic bleeding is different: it may leave only a small amount of blood in the stool, or show up as anemia on a blood test[16].
See a doctor soon if
What to do about each sign
If you noticeWhat to do

Any blood on or in the stool, even a littleBook a visit; bleeding needs a cause[3][8]
Diarrhea, constipation or thin stools for more than a few daysBook a visit and describe how long it has lasted[2]
Tiredness, pale skin or breathlessness with low ironAsk whether the bowel should be checked[3][10]
Hemorrhoid symptoms after 1 week of home careSee a doctor[8]
No symptoms and age 45 or olderAsk which screening test fits you[15]

Practical checklist before your visit

Write down when each symptom started and how often it happens.
Note the blood color: bright red, dark red or black.
Track any weight change over the last few months.
List close relatives who had colorectal cancer or polyps, and at what age.
Bring a list of your medicines and supplements.
If you have symptoms, ask for a diagnostic workup, not a screening blood test[12][15].

We built this checklist from the sources above, following our how we review health sources process and our editorial policy. More bowel and digestion guides sit in our gut, liver and detox section.
Bottom line
Most rectal bleeding and bowel changes turn out to be hemorrhoids, infection or IBS[3]. The ones that are cancer do far better when found early, with 91.3% five-year survival for local disease[5]. A quick visit to rule it out costs little next to that gap.
For anyone with symptoms, colonoscopy is the better first step than a blood test, because it can find the cause, take a biopsy and remove polyps in one visit[1][14]. The Shield blood test is a screening option for people without symptoms who will not do a stool test or colonoscopy, and a positive result still leads to a colonoscopy[12].

## Frequently asked questions

### Is colon cancer curable if it is found early?

Often, yes. SEER data show 91.3% of people whose colorectal cancer is found while still local are alive five years later. Surgery is the most common treatment, and cancer inside a polyp can often be removed during a colonoscopy.

### How long can you have colon cancer without knowing?

Months, sometimes longer. Early colon cancer often has no symptoms. In a 2023 study of younger patients, about one in five had a first warning symptom between 3 months and 2 years before diagnosis, a median of 8.7 months.

### Can a CEA blood test diagnose colon cancer?

No. CEA can be raised in colon cancer, but normal cells release it too. The American Cancer Society says CEA cannot be used alone to screen for or diagnose cancer. Doctors use it mostly to track a known cancer.

### How common is colon cancer in the US?

It is common. SEER estimates 158,850 new colorectal cancer cases in 2026, and ACS expects about 55,230 deaths. Combined, colon and rectal cancer are the second most common cause of cancer death in the US.

### Is a colonoscopy risky?

The risk is low. NIDDK puts perforation at about 3 and bleeding at about 15 per 10,000 procedures. The test usually takes under an hour and lets the doctor take a biopsy and remove polyps in the same visit.

## Sources

1. [Colon Cancer Treatment (PDQ), Patient Version](https://www.cancer.gov/types/colorectal/patient/colon-treatment-pdq). National Cancer Institute
2. [Colorectal Cancer](https://medlineplus.gov/colorectalcancer.html). MedlinePlus, National Library of Medicine
3. [Colorectal Cancer Signs and Symptoms](https://www.cancer.org/cancer/types/colon-rectal-cancer/detection-diagnosis-staging/signs-and-symptoms.html). American Cancer Society
4. [Key Statistics for Colorectal Cancer](https://www.cancer.org/cancer/types/colon-rectal-cancer/about/key-statistics.html). American Cancer Society, 2026
5. [Cancer Stat Facts: Colorectal Cancer](https://seer.cancer.gov/statfacts/html/colorect.html). NCI SEER Program, 2026
6. [Red-flag signs and symptoms for earlier diagnosis of early-onset colorectal cancer (Fritz et al.)](https://pubmed.ncbi.nlm.nih.gov/37138415/). Journal of the National Cancer Institute, 2023
7. [Why Is Colorectal Cancer Rising Rapidly among Young Adults?](https://www.cancer.gov/news-events/cancer-currents-blog/2020/colorectal-cancer-rising-younger-adults). National Cancer Institute, 2020
8. [Symptoms and Causes of Hemorrhoids](https://www.niddk.nih.gov/health-information/digestive-diseases/hemorrhoids/symptoms-causes). NIDDK
9. [Gastrointestinal Bleeding](https://medlineplus.gov/gastrointestinalbleeding.html). MedlinePlus, National Library of Medicine
10. [Iron-Deficiency Anemia](https://www.nhlbi.nih.gov/health/anemia/iron-deficiency-anemia). NHLBI
11. [Tests to Diagnose and Stage Colorectal Cancer](https://www.cancer.org/cancer/types/colon-rectal-cancer/detection-diagnosis-staging/how-diagnosed.html). American Cancer Society
12. [Shield P230009 (Recently-Approved Devices)](https://web.archive.org/web/2025/https://www.fda.gov/medical-devices/recently-approved-devices/shield-p230009). US Food and Drug Administration, 2024
13. [A Cell-free DNA Blood-Based Test for Colorectal Cancer Screening (ECLIPSE, Chung et al.)](https://pubmed.ncbi.nlm.nih.gov/38477985/). New England Journal of Medicine, 2024
14. [Colonoscopy](https://www.niddk.nih.gov/health-information/diagnostic-tests/colonoscopy). NIDDK
15. [Colorectal Cancer: Screening](https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/colorectal-cancer-screening). US Preventive Services Task Force, 2021
16. [Symptoms and Causes of GI Bleeding](https://www.niddk.nih.gov/health-information/digestive-diseases/gastrointestinal-bleeding/symptoms-causes). NIDDK

General information from JillLebofsky, not medical advice.