Colorectal cancer

What is colorectal cancer?

Colorectal cancer is a cancer of the colon or rectum, the lower part of the digestive tract. Most cases develop slowly from polyps over five to ten years, so screening can find and remove them early. It is one of the most common cancers in Singapore, and early-stage disease is far more treatable than late-stage disease.

The colon and rectum make up the large bowel. Most colorectal cancers begin as a polyp, a small growth on the lining that may turn cancerous over five to ten years. Early cancer often causes no symptoms, which is why regular screening matters even when you feel well.

What causes colorectal cancer?

Risk rises with age, particularly from 50, and with a family history of bowel cancer or polyps, inherited conditions such as Lynch syndrome, and long-standing inflammatory bowel disease. Diets high in processed and red meat, smoking, heavy alcohol use, obesity and inactivity also add risk.

• Age, with risk rising from around 50
• A family history of colorectal cancer or polyps
• Inherited conditions such as Lynch syndrome
• Long-standing inflammatory bowel disease
• Diets high in processed and red meat
• Smoking, heavy alcohol use, obesity, and inactivity

What are the symptoms?

Colorectal cancer often causes no symptoms early on. Later signs include blood in or on the stool, a lasting change in bowel habit, unexplained weight loss or tiredness, abdominal pain or bloating, and iron deficiency anaemia. These also have harmless causes, but they need checking.

• Blood in or on the stool
• A persistent change in bowel habits
• Unexplained weight loss or tiredness
• Abdominal pain or bloating
• A feeling the bowel does not empty fully
• Iron deficiency anaemia

When should I see a colorectal surgeon?

See a doctor promptly for new rectal bleeding, a change in bowel habit that lasts more than a few weeks, or unexplained weight loss. Go to an emergency department for severe pain, repeated vomiting or a blocked bowel. Screening is advised from age 50 without symptoms, and earlier with a family history.

The warning signs below need prompt attention.

• Any new bleeding or change in bowel habits that lasts
• Weight loss you cannot explain
• A family history with a young relative affected
• Severe pain, vomiting, or a blocked bowel

How is it diagnosed?

Diagnosis starts with a colonoscopy to see the tumour and take a biopsy. A CT scan checks whether the cancer has spread, and blood tests, including tumour markers, help with staging and follow-up. The results are discussed together to decide the treatment plan, with an oncologist where needed.

• Colonoscopy to inspect the bowel and take a biopsy
• CT scan to see whether cancer has spread
• Blood tests including tumour markers
• MRI or ultrasound for rectal cancer
• Staging work to plan the right treatment

How common is colorectal cancer in Singapore?

Colorectal cancer is the second most common cancer in Singapore, affecting about 45 in every 100,000 people. Nearly 13,000 cases were diagnosed between 2019 and 2023. It is most often found in people aged 50 and above, but it is becoming more common in younger adults, so symptoms should not be dismissed because of age.

Screening is recommended from age 50 for people without symptoms, using a yearly faecal immunochemical test (FIT) or a colonoscopy every 5 to 10 years. People with a family history start earlier. Because most bowel cancers grow from polyps over several years, screening can prevent cancer as well as find it at an earlier, more treatable stage.

• Average risk: start screening at 50 with yearly FIT or colonoscopy
• A close relative diagnosed at 60 or younger, or two or more close relatives: colonoscopy from age 40, or 10 years before the youngest case in the family, whichever is earlier, then about every 5 years
• A close relative diagnosed over 60: colonoscopy from age 50
• Known or suspected hereditary syndrome: earlier and more frequent checks with genetic counselling
• Long-standing ulcerative colitis or Crohn's colitis: regular colonoscopy surveillance after several years of disease

What do the stages of colorectal cancer mean?

Stage describes how far a bowel cancer has grown and spread. Stage 1 is within the bowel wall. Stage 2 has grown through the wall but not into lymph nodes. Stage 3 has reached nearby lymph nodes. Stage 4 has spread to distant organs such as the liver or lungs. Stage guides treatment.

Doctors usually describe the stage using the TNM system, which records the size and depth of the tumour (T), whether lymph nodes are involved (N) and whether there is distant spread (metastasis, M). You may also hear the older Dukes' system. Scans give a stage before treatment, but in some cases the full extent of the cancer is only known once the removed bowel and lymph nodes have been examined after surgery.

• Stage 0 (carcinoma in situ): abnormal cells are confined to the inner lining, with little risk of spread
• Stage 1: the cancer has grown through the inner lining or into the muscle of the bowel wall, with no spread to lymph nodes
• Stage 2: the cancer has grown into the outer wall or into nearby tissue or organs, still without lymph node spread
• Stage 3: the cancer has spread to nearby lymph nodes but not to distant parts of the body
• Stage 4: the cancer has spread to distant parts of the body such as the liver or lungs; this is also called metastatic or advanced bowel cancer
• Grade is separate from stage and describes how the cancer cells are likely to behave

What tests are done after a diagnosis?

After a biopsy confirms cancer, scans and blood tests show how far it has spread. Imaging of the chest, abdomen and pelvis, usually by CT, is standard. Rectal cancers also need an MRI of the pelvis. Blood tests include the tumour marker CEA, and the tumour is tested for genetic features. A specialist team then agrees a plan.

The multidisciplinary team, sometimes called a tumour board, brings together colorectal surgeons, medical and radiation oncologists, radiologists and other specialists such as palliative care doctors where needed. Reviewing every result together means the order of treatment, for example whether radiotherapy or chemotherapy should come before surgery, is decided before anything starts.

• CT scan of the chest, abdomen and pelvis to look for spread to the liver, lungs or lymph nodes
• MRI of the pelvis for rectal cancer, to show how deeply the tumour has grown and its relation to nearby structures
• Carcinoembryonic antigen (CEA) blood test, a marker that can be raised in bowel cancer and is also used in follow-up
• Molecular testing of the tumour, including mismatch repair or microsatellite instability testing, which can point to Lynch syndrome and guide some drug treatments
• Fitness assessment with the anaesthetic team before surgery

How does treatment differ for colon and rectal cancer?

Colon cancer is usually treated with surgery first, followed by chemotherapy for some stage 2 and stage 3 cancers. Rectal cancer sits in the narrow pelvis close to the sphincter, so treatment is planned on the pelvic MRI. Many rectal cancers that are larger or involve lymph nodes are treated with radiotherapy or chemoradiotherapy before surgery.

For colon cancer, the section of bowel containing the tumour is removed with nearby lymph nodes, and the two ends are usually joined. Chemotherapy after surgery, for up to 3 to 6 months, may be offered to lower the risk of the cancer returning.

For rectal cancer, UK national guidance advises against routine radiotherapy before surgery for early tumours that have not reached lymph nodes, and recommends radiotherapy or chemoradiotherapy before surgery for more advanced local disease. Surgery removes the part of the rectum containing the cancer, with nearby tissue and lymph nodes. After sphincter-preserving rectal surgery, some people have bowel changes such as urgency, frequency or difficulty telling wind from stool, known as low anterior resection syndrome. These symptoms should be reported so they can be assessed and managed.

Even when cancer has spread, treatment can still help. Some people with limited spread to the liver, lungs or abdominal lining may be suitable for surgery combined with chemotherapy, planned with the relevant specialist surgeons.

• Very early cancers may be removed with only the growth or part of the inner lining, sometimes during colonoscopy
• Colon cancer: surgery, with chemotherapy afterwards depending on stage and risk features
• Rectal cancer: pelvic MRI, then surgery alone or radiotherapy or chemoradiotherapy first, depending on stage
• Advanced cancer: chemotherapy, targeted medicines or immunotherapy, sometimes with surgery for limited spread

What treatments are used today?

Surgery is an important treatment for many colorectal cancers that have not spread. Depending on the cancer, treatment may also include chemotherapy, radiotherapy, targeted medicines or immunotherapy. Your multidisciplinary team, which includes your surgeon and oncologists, discusses the options with you, and the plan depends on the stage and the features of the tumour.

When chemotherapy is recommended after colon cancer surgery, FOLFOX or CAPOX, also called CAPEOX, may be given for 3 or 6 months. The choice depends on recurrence risk, the regimen and possible side effects. Radiotherapy, sometimes combined with chemotherapy, is mainly used for rectal cancer. For selected locally advanced rectal cancers, planned chemotherapy and radiotherapy are given before surgery. Some patients with a complete response may be offered close surveillance instead of immediate surgery.

Testing the tumour for mismatch repair deficiency or microsatellite instability is recommended for everyone newly diagnosed with colorectal cancer. Checkpoint inhibitor immunotherapy can be an option for some mismatch repair deficient or MSI-high cancers, including advanced colorectal cancer and selected locally advanced rectal cancers. It does not work for everyone.

For metastatic colorectal cancer, RAS and BRAF V600E testing helps guide treatment. Some cancers with a BRAF V600E mutation may be treated with a targeted drug combination, and other tumour markers can also influence the choice. If spread to the liver, lungs or abdominal lining is limited, a specialist team may consider surgery or another local treatment, sometimes alongside systemic treatment. In selected patients, the aim may be long-term control or cure.

• Surgery: open, laparoscopic or robot-assisted, depending on the cancer and the patient
• Chemotherapy: FOLFOX or CAPOX may be given for 3 or 6 months after colon cancer surgery when recommended
• Radiotherapy, sometimes with chemotherapy: mainly for rectal cancer
• Treatment before surgery: planned chemotherapy and radiotherapy for selected locally advanced rectal cancers
• Immunotherapy: an option for some mismatch repair deficient or MSI-high cancers
• Targeted medicines: guided by RAS, BRAF V600E and other tumour tests in metastatic disease
• Surgery or local treatment for limited spread: in selected patients

What are keyhole surgery and enhanced recovery?

Keyhole (laparoscopic) surgery removes the cancer through several small cuts instead of one long one. Where it is suitable, it is linked with less pain and quicker recovery. Enhanced recovery after surgery (ERAS) is a planned care pathway that prepares your health before the operation and helps you regain normal function sooner afterwards.

National guidance recommends laparoscopic surgery for both colon and rectal cancer when it and open surgery are both considered suitable. Open surgery may be better for some locally advanced tumours or after several previous abdominal or pelvic operations, and occasionally a keyhole operation has to be converted to an open one during surgery. Robotic surgery is another minimally invasive approach used within established programmes. The choice of approach depends on the tumour and on you, and is discussed before surgery.

• Before surgery: clear information about the operation and the recovery plan, and steps to get your general health as good as it can be
• After surgery: a planned, step-by-step return to eating, moving and normal function
• Throughout: you are told what the pathway involves and why each step matters, so you can take an active part

Will I need a stoma?

Not everyone having bowel cancer surgery needs a stoma, and many stomas are temporary. A temporary stoma is sometimes made to divert stool while a join low in the rectum heals, and is closed in a later operation. A permanent colostomy may be needed when the cancer is very close to the anus and the whole rectum is removed.

A stoma is an opening on the abdomen where the bowel is brought to the skin and stool collects in a bag. A colostomy is made from the large bowel and an ileostomy from the small bowel. Before surgery you should be told how likely a stoma is, why it might be needed and how long it may stay. Specialist stoma nurses help you and your family learn to care for it and to live with it day to day.

• Temporary stoma: diverts stool while a low join heals, then is reversed once healing is confirmed
• Permanent colostomy: when the cancer is too close to the anus for the bowel to be rejoined
• Either a colostomy or an ileostomy may be used, depending on the operation
• Specialist stoma nurses support you before and after surgery

What does follow-up look like after surgery and chemotherapy?

Follow-up looks for a possible return of cancer and for new cancers or polyps. If the whole bowel was examined around the time of surgery, a surveillance colonoscopy is generally recommended 1 year later. If clear, the next is 3 years after that, then 5 years later and every 5 years while appropriate. Your schedule may differ.

These colonoscopy intervals come from the US Multi-Society Task Force on Colorectal Cancer (2016), for people who have had surgery intended to remove all the cancer. If a blockage prevented a complete examination, a clearing colonoscopy is generally done 3 to 6 months after surgery, and surveillance follows 1 year after that clearing examination. If a polyp is found, your doctor will set the next interval according to its type and other findings. Lynch syndrome and some rectal cancer treatments need a different schedule.

For some people, particularly after stage 2 or 3 cancer, follow-up may include CEA blood tests every 3 to 6 months for 2 years, then every 6 months to year 5, and CT scans every 6 to 12 months for up to 5 years. Guidelines differ on how often, and your team will tailor the schedule. A new or rising CEA should be assessed by your team. They may repeat the blood test or arrange a CT scan or other investigation, depending on the result and your circumstances.

Follow-up is also a chance to discuss bowel function, energy, mood and any family screening that may be appropriate.

• Colonoscopy: generally 1 year after surgery or the clearing colonoscopy, then 3 years later, then 5 years later and every 5 years while appropriate, if clear
• CEA blood test: for some people, every 3 to 6 months for 2 years, then every 6 months to year 5
• CT scan of the chest, abdomen and pelvis: for some people, every 6 to 12 months for up to 5 years
• A new or rising CEA is assessed by your team
• Tell your care team about new symptoms rather than waiting for your next scheduled visit

Which inherited conditions raise the risk of bowel cancer?

A small share of bowel cancers are caused by inherited gene changes. The two main ones are Lynch syndrome and familial adenomatous polyposis (FAP). Both are passed on in families, with a 50 percent chance of a parent passing the gene change to each child. Relatives may need genetic counselling and earlier, more frequent bowel checks.

Lynch syndrome, also called hereditary non-polyposis colorectal cancer, is caused by changes in DNA mismatch repair genes. It raises the risk of bowel cancer and of other cancers, including cancer of the womb lining, ovaries, stomach and urinary tract. Polyps appear at a younger age but not in larger numbers. UK guidance suggests that daily aspirin taken for more than 2 years can be considered to lower bowel cancer risk in people with Lynch syndrome.

Classic FAP causes hundreds to thousands of polyps, which can start as early as childhood. Without treatment, at least 90 percent of people with classic FAP develop bowel cancer by age 50, so preventive removal of the large bowel is usually planned at the right time. A milder form, attenuated FAP, has fewer polyps that appear later.

• Genetic counselling and testing are advised for families with a known or suspected inherited syndrome
• Lynch syndrome: colonoscopy is usually advised from the early twenties, every 1 to 2 years
• FAP: bowel checks with a flexible camera usually start around age 10 to 12 and are repeated every year
• Tumour testing after a diagnosis can show features that suggest Lynch syndrome and prompt testing of the family

How is colorectal cancer treated?

Surgery to remove the section of bowel containing the cancer, with nearby lymph nodes, is the main treatment for most colorectal cancers. Keyhole (laparoscopic) surgery is used where suitable. Chemotherapy, radiotherapy or other treatment may be added depending on the stage and location, and the plan is made with you.

• Surgery to remove the affected section and nearby lymph nodes
• Minimally invasive laparoscopic surgery where suitable
• Chemotherapy before or after surgery
• Radiotherapy for some rectal cancers
• Polypectomy at colonoscopy for very early disease
• Long-term surveillance after treatment

What are the risks and complications?

Bowel surgery carries risks that include bleeding, infection, a leak at the join in the bowel, blood clots and anaesthetic complications. Some patients need a temporary or permanent stoma. Dr Wong explains your own risks, and how likely each is, before you consent.

• Bleeding and infection after surgery
• Leakage at the joined bowel
• Temporary or permanent stoma in some rectal cases
• Blood clots and the usual risks of anaesthesia
• Side effects from chemotherapy