Written with men in mind. Most of this guide applies to everyone. Details specific to women — such as screening ages and risks that differ — are not covered yet; female health guides are being written.
What it is
Colorectal cancer starts in the colon or rectum, the last parts of the digestive tract. Most begin as small growths called polyps on the inside lining. Some polyps can turn into cancer over years — which is why screening that finds and removes them can prevent cancer.[1][2]
The colon runs as ascending, transverse, descending and sigmoid segments before the rectum. Most colorectal cancers are adenocarcinomas arising from adenomatous polyps of the mucosa.[3] Screening tests either look for blood or altered DNA in stool, or look directly at the bowel lining.[4]
Adenocarcinoma arises through an adenoma–carcinoma sequence; tumours invade through the bowel wall layers to regional lymph nodes and, most commonly, the liver and lungs via haematogenous spread. Staging uses depth of invasion, nodal involvement and distant metastasis.[3][5] About 5% of cases are linked to inherited syndromes such as Lynch syndrome and familial adenomatous polyposis.[6]
See the colon framing the abdomen in 3D.
See it in 3DThe rectum is not a separate part in this model; it continues down from the sigmoid colon, which is shown.
How common it is
The American Cancer Society estimates about 108,860 new colon cancers and about 49,990 new rectal cancers in the US in 2026 — including about 55,410 and 28,750 in men — and about 55,230 deaths.[7] Men are more likely than women to die from colorectal cancer.[6]
Causes and risk factors
Things you can't change
- Age — much more common after 50, though younger adults can get it.[6]
- Personal history of adenomatous polyps, colorectal cancer, inflammatory bowel disease, or radiation to the abdomen or pelvis.[6]
- Family history of colorectal cancer or adenomatous polyps in a parent, sibling or child — especially if diagnosed before 50.[6]
- Inherited syndromes such as Lynch syndrome.[6]
Things you can change
Symptoms worth reporting to a doctor
- A change in bowel habits — diarrhoea, constipation or narrower stools — lasting more than a few days
- Feeling you need a bowel movement that isn't relieved by having one
- Rectal bleeding with bright red blood
- Blood in the stool, which can make it look dark brown or black
- Cramping or belly pain
- Weakness and tiredness
- Losing weight without trying
These are often caused by something other than cancer, such as haemorrhoids or infection — but they should be checked, whatever your age.[8]
Screening: who, when and how
The US Preventive Services Task Force recommends screening at 45–49 (grade B) and 50–75 (grade A); at 76–85 clinicians should selectively offer it (grade C).[4] Recommended options and intervals:[4]
- High-sensitivity stool test (FIT or gFOBT): every year
- Stool DNA-FIT: every 1–3 years
- CT colonography: every 5 years
- Flexible sigmoidoscopy: every 5 years (or every 10 years plus a yearly FIT)
- Colonoscopy: every 10 years
A positive stool test or CT colonography needs a follow-up colonoscopy. People with a strong family history or other high-risk factors may need to start earlier — ask your clinician.[4][6]
How it's diagnosed
Stages in general terms
In general terms:[5]
- Localised: confined to the inner layers of the bowel wall.
- Regional: grown through the wall or into nearby lymph nodes.
- Distant: spread to organs such as the liver or lungs.
An illustration, not a stage. Human Atlas never assigns a stage. Only your own tests and your care team can do that.
Types of treatment
- Surgery. Removing a polyp or the affected section of bowel with nearby lymph nodes.[3]
- Chemotherapy. Often after surgery when lymph nodes are involved, or for advanced cancer.[3]
- Radiation therapy. Used more often for rectal cancer.[3]
- Targeted therapy and immunotherapy. For some cancers with specific features, often advanced ones.[3]
Which option fits depends on the details of each person’s situation. Your care team decides with you.
What you can do
Get screened from 45
Pick a test you'll actually do — a home stool test counts. Earlier if you have a family history.[4]
Questions to ask your doctor
- Which screening test is right for me, and how often?
- Does my family history mean I should start earlier?
- If my stool test is positive, how soon should I have a colonoscopy?
- What did my colonoscopy find, and when is my next one?
- If I have cancer, what is its stage and what are my treatment options?
Myth vs. fact
Guided lesson
Plus Chapter 1 is free for everyone.
Follow this topic step by step on the 3D body.
Start chapter 1 freeRelated topics
Inguinal (groin) hernia
A bulge in the groin where tissue pushes through a weak spot in the belly wall. About 1 in 4 men get one in their lifetime.
Type 2 diabetes and prediabetes
Blood sugar that stays too high. Millions have it without knowing — and prediabetes can often be stopped from progressing.
Understanding cancer: the basics
What cancer is, how screening differs from diagnosis, what 'stage' means, and the main types of treatment — in plain English.
Sources
- National Cancer Institute. Colorectal Cancer Screening (PDQ®) – Patient Version. Checked 23 October 2026.
- National Cancer Institute. Colorectal Cancer Prevention (PDQ®) – Patient Version. Checked 23 October 2026.
- National Cancer Institute. Colon Cancer Treatment (PDQ®) – Patient Version. Checked 23 October 2026.
- US Preventive Services Task Force. Colorectal Cancer: Screening (May 2021). Checked 23 October 2026.
- National Cancer Institute. Cancer Staging. Checked 23 October 2026.
- American Cancer Society. Colorectal Cancer Risk Factors. Checked 23 October 2026.
- American Cancer Society. Key Statistics for Colorectal Cancer (2026 estimates). Checked 23 October 2026.
- American Cancer Society. Colorectal Cancer Signs and Symptoms. Checked 23 October 2026.
- US Department of Health and Human Services. Physical Activity Guidelines for Americans: Top 10 Things to Know. Checked 23 October 2026.
The owner of this website is not a doctor. Human Atlas provides educational anatomy information and does not diagnose, stage, or treat disease. Talk to a qualified clinician about anything concerning your own health.