Colon Cancer

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Colon cancer at a glance

This guide covers adenocarcinoma, the most common type of colon cancer, which starts in the gland-forming cells of the bowel lining. Neuroendocrine tumours, gastrointestinal stromal tumours, lymphomas, sarcomas and anal cancers follow different pathways.

Colon cancer starts in the large bowel above the rectum. It is often curable when confined to the bowel and nearby lymph nodes, and some cancers that have spread can still be treated with the aim of a cure.

Colon is not the same as rectum

Understand

The colon: route, segments and function

The colon absorbs water and salts, turns bowel contents into formed stool and moves stool towards the rectum. The side of the tumour can influence symptoms and metastatic treatment choices.

From normal lining to invasive cancer

Most colon cancers develop through accumulated cell changes over years. Removing pre-cancerous polyps during colonoscopy can prevent some cancers.

1. 1

   Normal lining

   Millions of lining cells renew in a controlled way.

2. 2

   A polyp forms

   An adenoma or serrated lesion grows from the inner lining. Most polyps are not cancer.

3. 3

   High-grade dysplasia

   Cells look very abnormal but have not grown through the thin muscle layer within the bowel lining (muscularis mucosae).

4. 4

   Invasive adenocarcinoma

   Cancer crosses into deeper bowel-wall layers and can enter lymphatic or blood vessels.

5. 5

   Regional or distant spread

   Cells may reach nearby lymph nodes, the liver, lungs, peritoneum or other sites.

A cancer found inside a removed polyp

Some malignant polyps need no further surgery if excision is complete and pathological risk is low. Deep submucosal invasion, poor differentiation, lymphovascular invasion, tumour budding, a close/positive margin or piecemeal removal may favour formal colectomy with lymph-node removal.

Symptoms can differ on the right and left

Colon cancer may cause no symptoms early. Persistent or unexplained changes deserve assessment even when piles, diet or infection seem possible explanations.

Symptoms anywhere in the colon

• Unexplained weight loss or reduced appetite.
• Persistent abdominal pain or bloating.
• A feeling that bowel habit has changed from your normal.
• A positive stool blood test, even if you feel well.

Risk, prevention and screening

Most people with colon cancer have no single cause. Risk factors change probability; they do not assign blame and do not prove why one person developed cancer.

Screening is for people without symptoms

Programmes use stool testing and/or colonoscopy according to age and risk. A positive stool test is not a cancer diagnosis; it identifies who needs colonoscopy. People with symptoms or high inherited risk need diagnostic or surveillance pathways, not routine screening alone.

Lynch syndrome, polyposis and germline testing

An inherited gene change that increases cancer risk can affect surgery, follow-up, treatment and advice for relatives. Tumour testing and germline testing answer different questions.

When to ask for genetic counselling

• Cancer at a young age, multiple primary cancers or many polyps.
• A close relative with colorectal, endometrial or related cancers, especially young.
• Loss of an MMR protein or MSI-high tumour without a clearly non-inherited explanation.
• A known familial pathogenic variant or a pattern that concerns your clinician.

Tests and diagnosis

How cancer is diagnosed

Diagnosis has three separate jobs: confirm cancer in tissue, define how far it has spread, and understand features that may change treatment.

1. 1

   Clinical assessment

   Your symptoms, bowel and medical history, family history, medicines, examination and ability to carry out everyday activities.

2. 2

   Blood tests

   Blood counts, iron levels, kidney and liver function, and a starting carcinoembryonic antigen (CEA) level. CEA is a blood marker used for later comparison; it can be normal even when cancer is present.

3. 3

   Colonoscopy

   Inspect the whole colon where possible, biopsy the lesion, remove other polyps and mark the site when helpful.

4. 4

   Pathology

   Confirm adenocarcinoma and report differentiation; later, the resection specimen defines depth, nodes and margins.

5. 5

   Staging scans

   Computed tomography (CT) chest/abdomen/pelvis is usual. Liver MRI, positron emission tomography combined with CT (PET-CT) or other tests answer selected questions.

6. 6

   Multidisciplinary team (MDT) review

   Surgeons, radiologists, pathologists and oncologists integrate results and treatment goals.

Colonoscopy, biopsy and the first report

Colonoscopy shows where the lesion is, whether it narrows the bowel and whether other polyps or cancers are present. The biopsy identifies the tumour type but cannot fully stage the bowel wall or lymph nodes.

If the scope cannot pass

CT colonography or colonoscopy after surgery may be used to assess the remaining colon. The plan depends on urgency and whether obstruction is present.

Scans and staging tests

Imaging looks for spread, resectability and complications. No single scan answers every question, and tiny deposits may remain below imaging resolution.

Before contrast or treatment

• Tell the team about previous contrast reactions, kidney disease, diabetes medicines and pregnancy possibility.
• Baseline blood counts and kidney/liver function guide scan safety and drug dosing.
• Frailty, nutrition, heart/lung function and daily activity can be as important as age.

Understanding your pathology report after surgery

The surgical specimen supplies the most reliable local stage. Ask for the pT, pN, margins, number of nodes examined and high-risk features as separate items.

Planning your treatment

How your treatment plan is chosen

The best plan combines anatomy, pathology, tumour biology, fitness and personal priorities. A single scan or single speciality should not decide a complex pathway alone.

Questions to ask your care team

• Is the goal cure, lower recurrence risk, conversion to resection, disease control or symptom relief?
• Is treatment urgent, and is there obstruction, perforation or severe anaemia?
• Which uncertainties could change the plan, and what test resolves them?
• What matters most to you: the chance of cure, avoiding nerve damage (neuropathy), work, fertility, avoiding a stoma or treatment close to home?

Treatment options

Colectomy: what may be removed

The surgeon removes the affected part of the colon together with its nearby lymph nodes, following the blood vessels and lymph drainage. The aim is to remove the cancer with a clear edge of healthy tissue around it and, when safe, join the remaining bowel.

What cancer surgery aims to achieve

• Remove the tumour-bearing colon segment with adequate margins.
• Remove the associated mesocolon and draining lymph nodes intact.
• Examine enough nodes for reliable staging.
• Restore bowel continuity when safe, or create a temporary/permanent stoma when needed.

Open, laparoscopic and robotic approaches

All three can be oncologically sound when performed by an appropriately trained team. Minimally invasive surgery often reduces wound pain and shortens recovery; open surgery may be safest for obstruction, bulky invasion, adhesions or multivisceral resection. Robotic surgery can help in selected anatomy but is not automatically superior.

Before agreeing to surgery

• Which part of the bowel and which lymph nodes will be removed.
• Chance of conversion to open surgery or removal of another organ.
• Risks of a leak where the bowel is joined, bleeding, infection, blood clots or a temporary slowing of bowel movement (ileus).
• Possibility and likely duration of a stoma.
• Enhanced recovery, pain plan and expected hospital stay.

Preparing, recovering and living with a stoma

Preparing your health and activity before surgery, then following a recovery plan, can reduce complications. A stoma is an opening made in the abdomen so stool can pass into a bag. It may be temporary or permanent, but many colon operations do not require one.

Stoma warning signs

• No output with cramps, swelling or vomiting.
• Very high watery output, dizziness, reduced urine or marked thirst.
• A dark/black stoma, severe pain, heavy bleeding or rapid swelling.
• Persistent leakage, broken skin or inability to keep the pouch on.

Stage II: do I need chemotherapy?

After the cancer has been completely removed, chemotherapy may treat cancer cells too small to see. In stage II, the extra benefit is often small. Your team will help you weigh the chance of the cancer returning against treatment side effects.

High-risk stage II features

• A tumour growing through the bowel’s outer covering or into a nearby organ (T4), a hole in the bowel (perforation) or bowel blockage.
• Fewer than 12 nodes examined when no clear explanation.
• Lymphovascular or perineural invasion, poor differentiation in an appropriate context, tumour budding or close/positive margin.
• Cancers with proficient mismatch repair (pMMR) or microsatellite stability (MSS) need a different treatment discussion from dMMR/MSI-H cancers.

1. 1

   Confirm pathology quality

   pT stage, at least 12 nodes where feasible, margins, obstruction/perforation, invasion and tumour budding.

2. 2

   Check MMR/MSI

   dMMR/MSI-H usually has a better stage II prognosis and changes fluoropyrimidine-alone benefit.

3. 3

   Estimate absolute benefit

   Ask for benefit in percentage points, not only relative-risk language.

4. 4

   Match treatment intensity

   Options include monitoring, a fluoropyrimidine medicine alone, or chemotherapy combinations called CAPOX or FOLFOX (explained below), depending on recurrence risk and overall health.

5. 5

   Include your priorities

   Consider nerve damage, work, other health conditions, fertility, travel and which side effects you feel able to manage.

Where ctDNA fits

Circulating tumour DNA (ctDNA) is DNA released by cancer cells that can be found in the blood. Finding it after surgery is linked to a higher risk of the cancer returning. It is increasingly used in trials and selected centres, but a negative result does not prove zero risk and should not automatically override established pathological features. Ask whether the proposed use is guideline-supported or research-based.

Stage III: treatment after surgery

Treatment after surgery aims to lower the risk of cancer returning. The choice depends on your MMR result, recurrence risk and overall health.

Chemotherapy options

Oxaliplatin combined with a fluoropyrimidine medicine, such as fluorouracil or capecitabine, lowers the risk of cancer returning after stage III surgery. CAPOX is oral capecitabine plus oxaliplatin; FOLFOX uses infusional fluorouracil, leucovorin and oxaliplatin.

How long does chemotherapy alone last?

For chemotherapy without atezolizumab, three months of CAPOX may be suitable for lower-risk stage III cancer (often T1–3, N1). This reduces nerve damage from oxaliplatin, with a small difference in cancer-control outcomes. Higher-risk cancer (T4 and/or N2) more often needs six months, particularly with FOLFOX. Your team will explain how your stage, treatment combination and side effects affect the choice.

Adding immunotherapy for stage III dMMR cancer

For stage III colon cancer with deficient mismatch repair (dMMR), atezolizumab with fluoropyrimidine and oxaliplatin chemotherapy is now an FDA-approved standard treatment option after the cancer has been completely removed by surgery. The approval was granted on 8 October 2026.

The ATOMIC trial tested atezolizumab with mFOLFOX6 for six months, followed by atezolizumab alone for a further six months. mFOLFOX6 is a schedule of fluorouracil, leucovorin and oxaliplatin. Adding atezolizumab reduced the risk of cancer returning or death compared with chemotherapy alone.

Your oncologist will confirm the dMMR result and whether this treatment suits you. Atezolizumab can cause the immune system to inflame healthy organs, so monitoring is important. Treatment may need to stop earlier if the cancer returns or side effects become unacceptable.

First-line treatment for metastatic colon cancer

The first decision is whether all the cancer can be removed by surgery (whether it is resectable). If not, systemic treatment is chosen from tumour biology, side, symptoms, fitness, organ function and the goal of therapy.

Right versus left matters

For RAS/BRAF wild-type disease, anti-EGFR therapy gives its clearest first-line benefit in left-sided primary tumours. Right-sided disease more often uses a chemotherapy plus anti-VEGF approach unless a biomarker-directed strategy applies.

How biomarkers guide treatment after cancer has spread

Tests for gene and protein changes in the cancer should be available early enough to guide treatment. These changes, called biomarkers, can help identify which treatments may work and in what order. “Wild-type” means that the tested gene does not have the particular changes being looked for.

HER2 options

Options include tucatinib plus trastuzumab for previously treated RAS wild-type HER2-positive unresectable/metastatic colorectal cancer. Trastuzumab deruxtecan is an antibody-drug conjugate with FDA accelerated approval for adults with HER2 IHC 3+ solid tumours that cannot be removed by surgery or have spread, after previous systemic treatment when no satisfactory alternative remains. This approval covers several cancer types, including colorectal cancer. Lung inflammation (interstitial lung disease) is an important risk that needs urgent assessment if suspected.

Newer treatment options

Treatment evidence is not a personal recommendation; biomarker confirmation, prior treatment and safety criteria still apply.

Liver- or lung-limited metastatic disease

Selected metastatic colon cancers can be treated with curative intent. The pathway needs coordinated oncology, liver/thoracic surgery, radiology and interventional expertise.

Common sites

1. 1

   Map all disease

   High-quality CT; liver MRI and selected PET-CT when they change a curative local plan.

2. 2

   Define technical and biological resectability

   Can all visible disease be cleared while preserving adequate liver or lung function?

3. 3

   Choose sequence

   Colon-first, liver-first, simultaneous surgery or systemic therapy first according to symptoms, burden and biology.

4. 4

   Use local tools deliberately

   Resection is established; ablation or stereotactic radiotherapy can complement surgery in selected lesions.

5. 5

   Reassess early

   Conversion therapy needs scheduled MDT review before too many cycles or avoidable liver injury/neuropathy.

6. 6

   Plan surveillance

   Recurrence can still be treatable; follow-up should retain surgical review when new limited disease appears.

Questions to ask the specialist team

• Is every lesion technically removable or ablatable now?
• How much working liver would remain after surgery? Would a procedure to help that part grow before surgery (portal-vein embolisation) be needed?
• Will chemotherapy improve resectability, or could it delay definitive surgery?
• What is the plan if scans show mixed response?

Later-line treatment, trials and supportive care

The next treatment depends on what has helped before, side effects, biomarker results, remaining nerve symptoms, organ function, current symptoms and time since previous treatment.

Supportive care is active treatment

• Pain, nausea, bowel function, appetite, sleep and mood.
• Anaemia, ascites, neuropathy, stoma and skin care.
• Advance-care planning and caregiver support alongside anticancer treatment.
• Honest discussion when treatment burden exceeds likely benefit.

Managing side effects

Chemotherapy side effects: act early

Most side effects can be reduced when reported early. Your treatment centre's 24-hour number and temperature threshold take priority over general advice.

Common supportive measures

• Anti-sickness medicines taken as prescribed, not only after severe nausea.
• Mouth care, hydration, gentle activity and nutrition support.
• Dose delay or reduction when recovery is incomplete; this is safety, not failure.
• Discuss fertility preservation before treatment when relevant.

Immunotherapy side effects

If you receive immunotherapy, contact your oncology team promptly about new or worsening diarrhoea, cough, breathlessness, yellowing of the skin or eyes, or severe unusual tiredness. Immune side effects can begin during or after treatment. Severe breathlessness, chest pain, confusion or collapse need urgent medical assessment.

Read about atezolizumab↗

Live well

Nutrition, bowel habit and physical activity

After colectomy, bowel function often changes before settling. The goal is adequate nutrition and hydration, then gradual return towards a varied high-quality diet rather than a permanently restrictive 'cancer diet'.

Activity is part of recovery

• Short frequent walks early; build time before intensity.
• Strength training supports muscle, function and treatment tolerance when cleared.
• After localised colon cancer, regular structured exercise is now specifically reinforced in current guidance.
• Stop and seek advice for chest pain, fainting, new breathlessness, calf swelling or severe abdominal pain.

Function, feelings, fertility and work

Recovery includes more than scans. Fatigue, neuropathy, bowel confidence, fear of recurrence, relationships, work and financial pressure deserve routine discussion.

Caregivers also need a plan

• A named contact in your care team.
• Shared medication and appointment record.
• Respite, sleep and help from family/community.
• Support to ask the team what to expect while respecting the choices of the person you care for.

Follow-up after treatment

Follow-up aims to find treatable recurrence, detect a new bowel lesion, manage late effects and restore general health. The exact schedule depends on stage and treatment.

Symptoms to report between appointments

• Persistent new abdominal pain, swelling or altered bowel habit.
• Blood in stool, unexplained weight loss, breathlessness or worsening fatigue.
• Jaundice, persistent cough, bone pain, new neurological symptoms or declining function.
• Any obstruction or treatment-emergency signs listed earlier.

Related care

Explore treatments

Medical Oncology↗Ports, PICCs, and venous access↗Stem Cell Transplant & Cellular Therapy↗Cancer Surgery↗Radiation Oncology↗Cancer Diagnostics & Molecular Testing↗Supportive & Holistic Cancer Care↗

Meet our doctors

Dr (Prof) Vijay Agarwal

Professor and Lead Consultant – Medical Oncology

Dr Prathyush V

Senior Consultant – Medical Oncology & Haemato-Oncology

Dr Darshan R S

Consultant – Medical Oncology & Haemato-Oncology

Where to get care

Bannerghatta Road

Apollo Hospitals
Bengaluru

Seshadripuram

Apollo Hospitals
Bengaluru

Sarjapur

Apollo Hospitals
Bengaluru

Jayanagar

Apollo Speciality Hospital
Bengaluru