Colorectal cancer

What is it?

According to the CDC: “When cancer starts in the colon or rectum, it is called colorectal cancer”. The colon is the large intestine, and the rectum is the passage that connects the colon to the anus. MedlinePlus explains that the colon is the first and longest part of the large intestine and the rectum is its lower part, and cancer that starts in the colon is called colon cancer and cancer that starts in the rectum is called rectal cancer. The NHS calls it “bowel cancer” and defines it as cancer anywhere in the large bowel including the colon and rectum. The colon is part of the digestive system (NCI).

Polyps: “abnormal growths called polyps sometimes form in the colon or rectum, and some may turn into cancer over time” (CDC). The NCI says colorectal cancer “often begins as a growth called a polyp inside the colon or rectum”.

Figures according to the WHO: the third most common cancer in the world with about 10% of cancer cases, and the second leading cause of cancer deaths; about 1.9 million new cases and more than 900,000 deaths were estimated in 2022. It mostly affects people aged 50 and over with a growing burden among adults aged 30 to 50 in some places, and it can cause severe illness and early death, especially when diagnosed at advanced stages.

Causes

The NHS says: “It is not always known what causes bowel cancer, but it may result from genetic changes and from lifestyle and environmental factors”. The CDC explains that some polyps may turn into cancer over time.

Inherited syndromes that raise risk: familial adenomatous polyposis (FAP) and Lynch syndrome (hereditary non-polyposis colorectal cancer) (CDC, WHO, NHS). The biopsy may also be tested to detect Lynch syndrome (NCI).

Risk factors

Age: “your risk of getting it goes up as you get older” (CDC), the NHS lists age over 50, and the WHO says risk rises markedly after 50.

Health conditions and family history: inflammatory bowel diseases such as Crohn's disease and ulcerative colitis (the NCI and MedlinePlus specify chronic ulcerative colitis or Crohn's disease for 8 years or more), a personal or family history of colorectal cancer or polyps, adenomas, and the inherited syndromes FAP and Lynch (CDC, MedlinePlus, NCI).

Lifestyle according to the WHO: a diet rich in processed and red meat and low in fruit and vegetables, physical inactivity, being overweight and obese, tobacco use, and alcohol consumption. The CDC lists physical inactivity, not keeping a healthy weight, alcohol and tobacco, and the NCI lists “having three or more alcoholic drinks a day”, cigarette smoking and obesity.

MedlinePlus and the NCI also list being Black among the risk factors in US data. This page's sources do not list type 2 diabetes as a risk factor.

Symptoms

“Polyps and colorectal cancer do not always cause symptoms”, so you may have it and not know (CDC). Symptoms according to the CDC include: a change in bowel habits, blood in or on the stool, diarrhoea or constipation or a feeling that the bowel does not empty completely, abdominal pain or cramps that do not go away, weight loss for no known reason, and low iron in the blood (anaemia).

The WHO lists: a change in bowel habits such as diarrhoea, constipation or narrowing of the stool, blood in the stool (bright red or dark tarry), abdominal cramps, pain or bloating that does not go away, unexplained weight loss, persistent tiredness, and iron-deficiency anaemia resulting from chronic bleeding. The NHS adds: needing to poo more or less often than usual, bleeding from the anus, repeatedly feeling the need to poo even after going, a lump in the abdomen, bloating, and severe tiredness or shortness of breath.

These symptoms may result from causes other than cancer, and “the only way to know the cause is to see a doctor” (CDC). The NHS says some are very common and do not necessarily mean you have it, but it is important to be checked by a doctor.

How is it diagnosed?

Diagnostic methods according to the WHO: clinical examination, imaging such as abdominal ultrasound, CT and MRI, examination of the inside of the colon by colonoscopy or sigmoidoscopy (see endoscopy), taking a biopsy for histological examination, and molecular tests to identify mutations or biomarkers that guide the choice of treatment.

The NCI lists: digital rectal examination, faecal occult blood tests (gFOBT and FIT), colonoscopy or sigmoidoscopy with the possibility of taking a biopsy, the biopsy (which is also tested to detect Lynch syndrome), and a blood test for carcinoembryonic antigen (CEA). For staging: CT, MRI, PET, chest X-ray and lymph node biopsy.

According to the NHS the main test is colonoscopy, in which “a thin, flexible tube with a camera is used to look inside the bowel” and a small sample of its lining may be taken. After diagnosis a CT, MRI or PET scan, blood tests and a genetic test may be requested to find the extent of spread and whether the cancer is caused by changes in genes.

Early detection: the WHO says regular screening, where organised screening programmes exist, is the most effective way to detect the disease early and prevent it by removing precancerous lesions, and that it reduces incidence and deaths. The CDC reports the US Preventive Services Task Force (USPSTF) recommendation to screen adults aged 45 to 75, that the decision between 76 and 85 is individual, and that people at higher risk (inflammatory bowel disease, personal or family history, FAP or Lynch) may need to start before 45 or be screened more often. Tests according to the CDC: stool tests (gFOBT and FIT yearly, FIT-DNA every 3 years), flexible sigmoidoscopy (every 5 years or every 10 with yearly FIT), colonoscopy (every 10 years for those without high risk), and CT colonography (every 5 years). Programmes and their ages differ between countries, and your doctor decides the test and timing that suit you.

Benefits and harms of screening according to the NCI: some screening tests detect cancer early and may reduce deaths, while “screening by digital rectal examination does not reduce the number of deaths”. Serious harms of colonoscopy include tears in the colon lining and bleeding, and sedation may cause heart and lung problems; sigmoidoscopy has fewer complications; and stool tests may give false-positive results that call for further tests. “Talk to your doctor about your risk and your need for screening”.

Treatment

The treatment categories usually used are listed here; this is not a prescription. The doctor chooses the plan according to each person's condition; do not change any medicine or dose without a specialist.

According to the NHS, treatment depends on the size of the cancer, whether it is in the colon, the rectum or both, its spread, the presence of certain genetic changes, and age and general health. MedlinePlus says the options usually depend on age, general health, and the severity and type of the cancer, and the NCI links prognosis and treatment options to the stage. The plan is set by the specialist team with the patient.

Surgery: “surgery may be done to remove the cancer from the bowel” (NHS). The NCI lists polypectomy, local excision, removal of part of the colon with joining of the ends, and if they cannot be joined “an opening (stoma) is made on the surface of the body for waste to leave”. A colostomy or ileostomy may be temporary or permanent (NHS). MedlinePlus and the NCI also mention radiofrequency ablation and cryosurgery. (See general surgery.)

Chemotherapy is “a medicine that kills cancer cells” and may be given before or after surgery, when surgery is not possible, or when the cancer has spread; radiotherapy is usually used for rectal cancer or when it has spread; targeted drugs and immunotherapy are sometimes used for advanced spread cancer (NHS). Targeted therapy categories the NCI lists include monoclonal antibodies, and immunotherapy includes immune checkpoint inhibitors. MedlinePlus lists active surveillance as an option in some cases of rectal cancer. (See oncology.)

According to the NHS the treating team explains the treatments, their benefits and side effects, works with you on the most suitable plan, and helps you deal with side effects. Do not start or stop any medicine without the medical team.

Follow-up

After colon cancer treatment, a blood test to measure carcinoembryonic antigen (CEA) may be done to see whether the cancer has come back (NCI). The NHS lists a team of specialists with a specialist clinical nurse who is the main point of contact during and after treatment. This page does not cover detailed follow-up schedules.

Complications

Spread: the NCI describes the stages according to whether only the inner lining of the colon is affected or it has spread to lymph nodes, nearby organs or other parts of the body, and the WHO says it can cause severe illness and early death especially with late diagnosis, and that prognosis depends strongly on the stage.

Iron-deficiency anaemia resulting from chronic bleeding (WHO, CDC). Surgery may require a temporary or permanent external opening (stoma) (NHS, NCI). When a cure is not possible the patient is referred to a symptom control or palliative care team (NHS).

Prevention

According to the WHO it can be prevented by a healthy lifestyle and early detection: a healthy diet rich in fruit and vegetables, no tobacco use, an active lifestyle, a healthy weight, limiting alcohol, and avoiding environmental risk factors. The NHS advises eating at least 5 portions of fruit and vegetables a day, being active, losing weight if overweight, quitting smoking, reducing alcohol, and cutting down on red and processed meat.

Screening is also prevention: “finding and removing polyps can prevent colorectal cancer” (NCI), and “screening tests can find polyps so they can be removed before they turn into cancer” (CDC). The CDC says: “If you are 45 or older, talk to your doctor about screening”. Programmes differ between countries.

Living with it

The treating team explains the treatments and their effects and helps deal with side effects, an external opening (stoma) may be temporary or permanent, and in advanced cases that cannot be cured the patient is referred to a symptom control or palliative care team (NHS). This page does not cover life after treatment.

Common questions