How Colorectal Cancer Begins and It's Symptoms
We tend to notice our bodies most when something hurts. A stomach ache. A change in bowel habits. Feeling unusually tired. Seeing blood where we don’t expect it.
Sometimes, these things have simple explanations. A stomach upset can be a stomach upset. Constipation can be constipation. Fatigue can come from a long week. But sometimes, the body keeps trying to tell us that something has changed.
Think of a car that has been driven for many years. One small fault appears: a warning light, a worn brake pad, a loose belt. The car still works, so it is easy to ignore. Then another problem appears. And another. Eventually, enough things begin to go wrong that the car is no longer safe to drive.
The point isn’t that every warning light means the car is about to stop working. It’s that small signs are worth paying attention to before they become bigger problems. Our bodies are not machines, of course, but the idea is useful when we think about conditions such as colorectal cancer.
What is Colorectal Cancer?
Let’s dive into some biology. When we eat food, it passes through the mouth, esophagus, and stomach before moving into the small intestine. Most nutrients are absorbed in the small intestine.
What remains then moves into the colon, where water is absorbed and waste is formed. The waste passes into the rectum and eventually leaves the body through the anus.
To put it very simply:
stomach → small intestine → colon → rectum → anus → outside the body
Normally, cells grow, repair themselves, and die in an orderly way. Cancer disrupts that process, allowing abnormal cells to keep multiplying. Over time, these abnormal cells can form a tumor, deepen into the wall of the bowel, or spread to other parts of the body.
Colorectal cancer can develop gradually, sometimes without obvious symptoms in its early stages. That makes awareness and screening particularly important. In the U.S., roughly 158,850 new cases are expected in 2026.
How Does Colorectal Cancer Begin?
Many colorectal cancers begin as polyps. A polyp is a growth that develops on the inner lining of the colon or rectum. Most polyps are not cancerous. However, some types can slowly develop into cancer over several years.
The process looks something like this:
This is one reason screening matters. If a precancerous polyp is found and removed before it becomes cancerous, the progression can sometimes be stopped before cancer develops.
Symptoms That Should Not Be Ignored
One of the difficult things about this type of cancer is that there may be no obvious symptoms early on. When symptoms do occur, they can also look like problems people commonly experience for other reasons.
Most common symptoms might include:
- Blood in or on the stool
- Very black or dark stools
- A persistent change in bowel habits
- Diarrhea or constipation that is unusual for you
- Stools becoming narrower than usual
- A feeling that the bowel has not completely emptied
- Abdominal pain, cramping or bloating that doesn’t go away
- Unexplained weight loss
- Ongoing tiredness or weakness
- Unexplained iron-deficiency anemia
However, these symptoms do not automatically mean cancer. Hemorrhoids, infections, irritable bowel syndrome, and other conditions can cause similar problems. The important thing is to notice when a change is persistent, unusual, unexplained, or getting worse.
Speak to a healthcare professional rather than trying to diagnose yourself. Seek urgent help for heavy bleeding, severe abdominal pain, repeated vomiting, or being unable to pass stool or gas.
Who Is More Likely to Develop Colorectal Cancer?
Colorectal cancer can affect people who have no obvious risk factors, but certain things can increase the chances of developing it.
These include:
- Increasing age
- Having had colorectal cancer or advanced polyps in the past
- A close family member with colorectal cancer or advanced polyps
- Inherited conditions such as Lynch syndrome or familial adenomatous polyposis
- Inflammatory bowel disease, such as Crohn's disease or ulcerative colitis
- Overweight or obesity
- Low physical activity
- Smoking
- Higher alcohol consumption
- Diets high in processed meat or large amounts of red meat.
Family history deserves particular attention.
If a close relative developed colorectal cancer at a young age, it may change when screening should begin or how frequently it should be performed.
But there is another important point.
Younger does not mean impossible.
Colorectal cancer is more common as people get older, but younger adults can develop it too. Persistent or unusual symptoms should not automatically be dismissed because someone is considered ‘too young’ to have colorectal cancer.
For instance, Pam was approaching 30 when she shared her experience of Stage IV colorectal cancer. She hadn’t noticed the typical bowel symptoms, and her cancer was discovered through medical investigations for other health concerns.
Jessica was 46 when she received a Stage IV colon cancer diagnosis. Unlike Pam, she experienced a serious bowel obstruction that required emergency treatment.
Their experiences are different, but both reinforce an important message: although colorectal cancer becomes more common with age, being younger does not rule it out.
Screening: finding problems before they become bigger problems.
Screening looks for colorectal cancer or precancerous polyps in people who do not have symptoms. In the United States, adults at average risk should generally begin screening at age 45 and continue through age 75.
Screening between ages 76 and 85 may be appropriate for some people, depending on their overall health, previous screening history, and preferences. When colorectal cancer is found before it has spread, about 9 out of 10 people are still alive five years after diagnosis.
But if it isn’t found until it has traveled to distant parts of the body, those odds drop significantly- leaving only about 1 in 6 people alive at that five-year mark. These figures describe large groups of people, not what will happen to one individual. Treatment continues to improve, and each person’s outlook depends on the cancer’s stage, biology, overall health, and response to treatment.
If a suspicious area is found, a biopsy may be taken. A pathologist examines the tissue to determine whether cancer is present. CT, MRI, or other scans may then be used to find out whether the cancer has spread. This is called staging.
Colorectal Cancer Doesn't Follow a Single Story
Colorectal cancer doesn’t follow one predictable path. Some people develop it later in life, while others face a diagnosis much younger than expected. Some have a family history or known risk factors, while others have no obvious reason to suspect anything is wrong.
What matters is understanding that risk factors are not guarantees, and having none does not mean someone is completely protected. Changes in bowel habits, persistent discomfort, or other unexplained symptoms deserve attention, regardless of age.
Knowing how colorectal cancer develops, recognizing possible warning signs, and understanding who may be at greater risk are important starting points. But awareness is only part of the picture.
Read more about how screening can help detect colorectal cancer early, what treatment may involve, and how people and their loved ones navigate life during and after a diagnosis.
References
- Centers for Disease Control and Prevention. About colorectal cancer. Available at: https://www.cdc.gov/colorectal-cancer/about/index.html. Accessed October 1, 2026.
- American Cancer Society. Colorectal cancer signs and symptoms. Available at: https://www.cancer.org/cancer/types/colon-rectal-cancer/detection-diagnosis-staging/signs-and-symptoms.html. Accessed October 3, 2026.
- National Cancer Institute. Cancer Stat Facts: Colorectal cancer. Surveillance, Epidemiology, and End Results Program. Available at: https://seer.cancer.gov/statfacts/html/colorect.html. Accessed October 3, 2026.
- National Cancer Institute. Colon cancer treatment (PDQ®): Patient version; rectal cancer treatment (PDQ®): Patient version. Available at: https://www.cancer.gov/types/colorectal/patient/colon-treatment-pdq. Accessed October 2, 2026.
- American Cancer Society. Colorectal cancer risk factors. Available at: https://www.cancer.org/cancer/types/colon-rectal-cancer/causes-risks-prevention/risk-factors.html. Accessed October 3, 2026.
- Colorectal Cancer Alliance. Live Navigator Helpline. Available at: https://colorectalcancer.org/resources-support/resources/live-navigator-helpline. Accessed October 4, 2026.
- Centers for Disease Control and Prevention. Colorectal cancer screening. Available at: https://www.cdc.gov/colorectal-cancer/screening/index.html. Accessed October 4, 2026
- National Cancer Institute. Support for cancer caregivers. Available at: https://www.cancer.gov/about-cancer/coping/caregiver-support. Accessed October 3, 2026.
- American Cancer Society. Living as a colorectal cancer survivor. Available at: https://www.cancer.org/cancer/types/colon-rectal-cancer/after-treatment/living.html. Accessed October 3, 2026.
- Colorectal Cancer Alliance. Screening & Prevention. Available at: https://colorectalcancer.org/screening-prevention/get-screened-45. Accessed October 5, 2026.
Nothing on this page is medical advice. Always discuss your options with your own care team.
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