Colon and rectal cancer

Colorectal cancer.

- The colon (large intestine) and rectum (the last part before the anus) absorb water and store stool.
- Most colorectal cancers start as a small growth called a polyp, which slowly turns into cancer over years.
- Common symptoms: blood in the stool, a change in bowel habit, tummy pain, and anaemia (low haemoglobin) causing tiredness.
- It can spread to the lymph nodes, and through the blood to the liver and lungs, or to the lining of the abdomen (peritoneum).
- It is becoming more common in younger people. Any rectal bleeding should be checked, not assumed to be piles.
Colon and rectal cancer are treated differently, and some test results change treatment completely. Tap a type on the map.
Why this matters: rectal cancer often needs treatment before surgery, colon cancer usually does not. And cancers with dMMR / MSI-high respond very well to immunotherapy.
- - Cancer in the colon, anywhere from the right side (near the appendix) to the sigmoid colon.
  - Usually treated with surgery first, then chemotherapy if needed.
  Treatment for colon cancer
- - Cancer in the last 12 to 15 cm of the bowel.
  - Lies close to the pelvic bones, bladder and sphincter muscles, so treatment is usually given before surgery to shrink it and protect the sphincter.
  Treatment for rectal cancer
- - About 15 out of 100 colorectal cancers have a fault in the genes that repair DNA, called dMMR or MSI-high.
  - These cancers respond very well to immunotherapy, sometimes so well that surgery can be avoided.
  - Some are caused by an inherited condition called Lynch syndrome, which also raises the risk of other cancers in the family.
  More about hereditary cancers

- CT scan of the chest, abdomen and pelvis checks for spread to the liver, lungs and lymph nodes.
- MRI of the pelvis is essential in rectal cancer. It shows how deep the cancer has grown and whether treatment is needed before surgery.
- PET-CT is used in some patients.

In stage 4 cancer, the tumour is tested for mutations that guide treatment:

Mutation	What it means
RAS (KRAS, NRAS)	If present, cetuximab and panitumumab do not work. If absent (RAS wild-type), they can be used.
BRAF V600E	Encorafenib with cetuximab.
HER2 amplification	HER2-targeted medicines.
KRAS G12C, NTRK	Specific targeted medicines (rare).

A liquid biopsy (blood test) can be used if tissue is not enough.

Before starting chemotherapy, immunotherapy or targeted therapy, these tests check that you are fit for treatment, and give a starting point to compare with later.

Test	Why it is done
CBC (complete blood count)	Haemoglobin, white cells and platelets. Treatment can lower them.
RFT (kidney function)	Many medicines are cleared by the kidneys; the dose may need to change.
LFT (liver function)	Many medicines are processed by the liver.
Viral markers: HBsAg, anti-HCV, HIV	Hepatitis B can flare up during treatment. If positive, a tablet is given to prevent this.
Blood sugar (and HbA1c if diabetic)	Steroids given with chemotherapy can raise blood sugar.
ECG and 2D Echo	Check the heart rhythm and pumping before treatment, as some medicines affect the heart.

Before immunotherapy, also:

Test	Why it is done
Serum TSH (thyroid)	Immunotherapy can affect the thyroid gland.
Serum cortisol (morning sample)	Immunotherapy can affect the adrenal and pituitary glands.

Sometimes needed, depending on your treatment:

Pregnancy test for women who could be pregnant.
Calcium and magnesium: for example before cisplatin or bone-strengthening injections.
Dental check-up before bone-strengthening injections (zoledronic acid or denosumab), as they can rarely affect the jaw bone.
Hearing test before cisplatin, in some patients.
Clotting tests (PT/INR) before a biopsy or chemoport.

Your doctor will choose the tests that apply to you. Some of them are repeated during treatment.

- In rectal cancer, the MRI decides whether treatment is given before surgery. Operating first can mean losing the chance to save the sphincter.
- A dMMR result can mean immunotherapy instead of chemotherapy and radiotherapy, sometimes avoiding surgery altogether.
- In stage 4, RAS and BRAF results decide which targeted medicine is added to chemotherapy.
- Waiting a week or two for these reports does not make the cancer worse.

The stage is worked out from the scans and, after surgery, from the removed tissue. Tap your stage on the map.
Treatment depends on whether the cancer is in the colon or rectum, the stage, and the MMR and mutation results. Tap your type and stage on the map.
- Choose your stage on the map.
  - 1. Surgery to remove the part of the colon with the cancer and nearby lymph nodes (often keyhole or robotic).
    2. Stage 1: no further treatment.
    3. Stage 2: chemotherapy only for high-risk features (such as a blocked or perforated bowel, too few nodes examined). Not needed if the cancer is dMMR.
    Side effects: surgery · chemotherapy
  - 1. Surgery.
    2. Chemotherapy after surgery: CAPOX for 3 months (lower risk) or 6 months (higher risk), or FOLFOX.
    3. If the cancer is dMMR: immunotherapy (atezolizumab) may be added to chemotherapy after surgery. In large dMMR cancers, immunotherapy before surgery is also being used.
    What the research shows
    IDEA: for lower-risk stage 3 colon cancer, 3 months of CAPOX worked almost as well as 6 months, with much less nerve damage.
    ATOMIC: in dMMR stage 3 colon cancer, adding atezolizumab to FOLFOX lowered the chance of recurrence.
    NICHE-2: short immunotherapy before surgery in dMMR colon cancer left no cancer or almost none in most patients.
    Side effects: surgery · chemotherapy · immunotherapy
- Choose your stage on the map.
  - 1. Surgery (TME, total mesorectal excision), or for very small early cancers, removal through the back passage (local excision).
    Side effects: surgery and stoma
  - 1. Usually treatment before surgery (total neoadjuvant therapy): chemotherapy and radiotherapy (short 5-day course or 5-week course with tablets), over about 4 to 6 months.
    2. Then a repeat MRI and endoscopy. If the cancer has completely disappeared, some patients can avoid surgery and be watched closely (watch and wait).
    3. Otherwise surgery (TME).
    4. If the cancer is dMMR: immunotherapy (dostarlimab) alone, for 6 months, can make the cancer disappear in almost all patients, avoiding surgery and radiotherapy.
    What the research shows
    RAPIDO and PRODIGE 23: giving chemotherapy as well as radiotherapy before surgery lowered the chance of spread to other organs.
    OPRA: about half of patients could keep their rectum with watch and wait after a complete response.
    Dostarlimab study (Cercek, 2022 onwards): in dMMR rectal cancer, the cancer disappeared in every patient treated, without surgery or radiotherapy.
    Side effects: radiotherapy · chemotherapy · surgery and stoma · immunotherapy
- 1. Chemotherapy (FOLFOX, FOLFIRI, CAPOX, or FOLFOXIRI) with a targeted medicine chosen by the mutation tests:
    - RAS wild-type, left-sided: cetuximab or panitumumab.
    - RAS mutation or right-sided: bevacizumab.
    - BRAF V600E: encorafenib with cetuximab, with FOLFOX.
    - HER2: trastuzumab with tucatinib, or trastuzumab deruxtecan (usually after first treatment).
  2. dMMR / MSI-high: immunotherapy (pembrolizumab, or nivolumab with ipilimumab) instead of chemotherapy.
  3. If the spread is limited to the liver or lungs: surgery or ablation after chemotherapy can cure some patients.
  4. Later options: trifluridine-tipiracil with bevacizumab, fruquintinib, regorafenib.
  Your doctor will advise NGS or RAS / BRAF testing before starting. Why
  What the research shows
  - KEYNOTE-177 and CheckMate 8HW: immunotherapy controlled dMMR cancer much longer than chemotherapy.
  - PARADIGM: in RAS wild-type left-sided cancer, panitumumab with chemotherapy helped patients live longer than bevacizumab.
  - BREAKWATER: encorafenib, cetuximab and FOLFOX helped patients with BRAF V600E cancer live longer.
  - SUNLIGHT: trifluridine-tipiracil with bevacizumab helped patients live longer in later treatment.
  Side effects: chemotherapy · targeted medicines · immunotherapy
Each treatment has its own side effects. Most can be prevented or managed. Tap a treatment on the map.
Fever of 38°C or more, or 4 or more loose stools in a day, needs urgent care. When to seek help urgently
- - Nausea and vomiting: well controlled with medicines given before and after chemotherapy.
  - Low blood counts and infection risk: fever of 38°C or more needs urgent care.
  - Tiredness, mouth sores, loose stools or constipation.
  - Oxaliplatin: tingling in fingers and throat with cold. Avoid cold drinks and touching cold things for a few days after each dose. Tingling and numbness
  - Capecitabine: loose stools and hand-foot syndrome (red, sore palms and soles). Moisturise and tell us early.
  More about chemotherapy · Side effects of your regimen
- - Cetuximab / panitumumab: acne-like rash on the face and chest, dry skin, nail fold infections, low magnesium.
  - Bevacizumab: high blood pressure, protein in urine, nosebleeds; it slows wound healing, so it is stopped before and after surgery.
  - Encorafenib: joint pains, tiredness, skin changes.
  More about targeted therapy · Side effects of your regimen
- - The immune system can affect normal organs: thyroid, skin (rash, itching), bowel (loose stools), lungs (cough, breathlessness) and liver.
  - These can happen months after starting, or even after stopping. Report any new symptom, even if it seems small.
  - Thyroid, cortisol and liver blood tests are checked regularly.
  More about immunotherapy · Side effects of your regimen
- - Loose stools, frequent passing of urine, and soreness of the skin around the back passage during treatment.
  - Later: changes in bowel habit, and effects on sexual function and fertility. Ask about sperm or egg storage before treatment.
- - Some patients need a stoma (bowel opening on the tummy), often temporary for 3 to 6 months after rectal surgery.
  - After rectal surgery, bowel habits can change: frequent or urgent stools (low anterior resection syndrome). It usually improves over months.
Looking after yourself during and after treatment. Tap a topic on the map.
- - A stoma nurse teaches you to care for it before you go home.
  - You can eat normally, work, travel and exercise. Drink plenty of fluids, especially with an ileostomy.
  - Tell us if the stoma changes colour, stops working for more than a day with vomiting, or the skin around it is very sore.
- - CEA blood test every 3 to 6 months, and a CT scan every 6 to 12 months, for the first 3 to 5 years.
  - Colonoscopy 1 year after surgery, then as advised.
  - If Lynch syndrome is found, family members should be tested. Hereditary cancers

This information is general. Your own treatment plan may be different. Please discuss it with your doctor.

Written and medically reviewed by Dr Prathyusha Eaga, MD, DM (Medical Oncology). Last reviewed: 12 October 2026. Based on NCCN and ESMO guidelines.

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