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Overview

What Is Colorectal Cancer?

Colorectal cancer is cancer that begins in the colon or rectum, which are parts of the large intestine. It develops when abnormal cells grow out of control and may form polyps or tumors in the inner lining. Some polyps are not cancerous, but certain types can become cancer over time. If untreated, colorectal cancer may grow into nearby tissues or spread to other parts of the body.

Symptoms

Symptoms of Colorectal Cancer

Early colorectal cancer may cause no noticeable symptoms, which is one reason screening is important. When symptoms occur, they can vary depending on the tumor’s location and size. These signs can also result from conditions other than cancer, so they do not confirm a diagnosis on their own.

  • Blood in the stool (rectal bleeding).
  • A persistent change in bowel habits.
  • Ongoing diarrhea.
  • Ongoing constipation.
  • Narrower stools than usual.
  • Abdominal pain or cramping.
  • Unexplained weight loss.
  • Unusual tiredness related to anemia.

DO NOT IGNORE PERSISTENT CHANGES

When symptoms need medical attention

Contact a healthcare professional promptly if you notice blood in the stool, persistent bowel changes, or symptoms that are worsening or do not go away. A medical assessment can identify the cause and determine whether further testing is needed; symptoms alone do not mean you have cancer.

Causes

What Causes Colorectal Cancer?

Colorectal cancer starts when changes in a cell’s DNA disrupt the normal controls on cell growth and cell death. The abnormal cells can multiply, form a growth, and eventually invade deeper layers of the colon or rectum. Over time, some cancer cells may enter lymph vessels or the bloodstream and spread.

How polyps and inherited changes may contribute

Some colorectal cancers develop from precancerous polyps after a series of acquired DNA changes. Inherited gene changes, such as those linked with Lynch syndrome or familial adenomatous polyposis, can increase risk from birth, while other changes develop during a person’s lifetime. Most cases are not caused by one identifiable event; age, family history, health conditions, lifestyle, and chance changes may all play a role.

Risk Factors

Risk Factors for Colorectal Cancer

Factors linked with higher risk

  • Smoking can increase the likelihood of developing colorectal cancer.
  • Regular or heavy alcohol use is associated with higher risk.
  • Low physical activity may contribute to colorectal cancer risk.
  • Excess body weight is linked with a higher risk.
  • A diet high in processed or red meat and low in fiber-rich plant foods may increase risk.

Side Effects & Complications

Complications and Treatment Side Effects

  • A tumor may cause a bowel obstruction.
  • A tumor can rarely cause a hole or perforation in the bowel.
  • Bleeding may lead to anemia.
  • Advanced disease or treatment may contribute to malnutrition.
  • Cancer and some treatments can increase the risk of blood clots.
  • Colorectal cancer may spread to distant organs such as the liver or lungs.

CALL THE CARE TEAM PROMPTLY

Symptoms that may signal a complication

Contact your oncology team promptly for fever, uncontrolled vomiting, severe abdominal pain or swelling, inability to pass stool or gas, heavy bleeding, chest pain, or sudden shortness of breath. Surgery, radiation, chemotherapy, and other treatments may also cause pain, bowel or bladder changes, diarrhea or constipation, fatigue, nausea, neuropathy, skin changes, sexual or fertility effects, or temporary or permanent ostomy-related changes.

Diagnosis & Staging

Diagnosis and Staging

Evaluation usually begins with a medical history and physical examination. Depending on the situation, testing may include stool-based tests, colonoscopy, a biopsy, and laboratory tests such as a blood count or tumor markers when clinically indicated. A biopsy examines tissue under a microscope and is often used to confirm cancer.

How staging guides treatment

StageGeneral meaning
0Abnormal cells remain in the innermost lining.
ICancer has grown into the bowel wall but has not reached nearby lymph nodes.
IICancer has grown more deeply or through the bowel wall without nearby lymph-node involvement.
IIICancer has spread to nearby lymph nodes.
IVCancer has spread to distant organs or tissues.

Treatment Options

Colorectal Cancer Treatment Options

SURGERY

Removes the tumor and, when needed, nearby lymph nodes or affected bowel.

CHEMOTHERAPY

Uses medicines that travel through the bloodstream to treat cancer before or after surgery or when it has spread.

RADIATION THERAPY

Uses focused radiation, especially in selected rectal cancers, to shrink or control tumors.

TARGETED THERAPY AND IMMUNOTHERAPY

Uses biomarker-guided medicines for cancers with particular molecular features.

LOCAL OR ABLATIVE TREATMENTS

May destroy or control selected tumors in specific situations, often when surgery is not suitable or when disease has spread.

Colorectal cancer treatment may combine several modalities, depending on the tumor’s location, stage, molecular features, overall health, and personal preferences. A multidisciplinary team may include surgeons, medical oncologists, radiation oncologists, pathologists, nurses, dietitians, and ostomy specialists.

Prevention & Screening

Prevention and Screening

Risk may be lowered by not smoking, limiting alcohol, staying physically active, and maintaining a healthy weight. Emphasizing fiber-rich foods while limiting processed meat and moderating red meat may also support colorectal health. These steps reduce risk but cannot prevent every case of colorectal cancer.

Screening options and timing

  • Average-risk adults generally begin screening according to current national guidance, often in midlife.
  • Screening may use stool tests or visual examinations such as colonoscopy.
  • A positive stool test usually needs follow-up diagnostic colonoscopy.
  • People with symptoms, a strong family history, inherited risk, or inflammatory bowel disease may need earlier or more frequent testing, so confirm timing with a clinician.

Outlook and Prognosis

Outlook and Prognosis

The outlook is generally more favorable when colorectal cancer is found before it spreads. Advanced disease can be more difficult to cure, but it may still be treated or controlled for some people with surgery, medicines, radiation, or supportive care. Outcomes vary widely between individuals.

Survivorship & Follow-up

Survivorship and Follow-Up

Follow-up after treatment commonly includes scheduled visits, physical examinations, selected blood tests such as CEA when appropriate, imaging, and repeat colonoscopy based on treatment history and the clinical plan. The schedule varies according to the cancer’s stage, treatment, recurrence risk, and overall health.

  • Watch for possible recurrence and report new or persistent symptoms.
  • Manage bowel or ostomy changes with guidance from the care team.
  • Address neuropathy and fatigue, which may persist after treatment.
  • Support nutrition and regular physical activity as recovery allows.
  • Discuss emotional health, sexual health, fertility, work, and relationships.

Branches

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Tests & Procedure

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Symptoms

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