When bowel cancer has spread to the liver, lung or lining of the abdomen and pelvis, this is known as advanced or metastatic (stage 4) bowel cancer. To control the cancer, slow its growth and manage symptoms such as pain, you may have a combination of chemotherapy, targeted therapy, radiation therapy and surgery. For some people, the best option may be to join a clinical trial.

Drug therapies

Advanced bowel cancer is commonly treated with drugs that reach cancer cells throughout the body. This is called systemic treatment, and includes chemotherapy, targeted therapy, and immunotherapy. 

Targeted therapy drugs work differently from chemotherapy drugs. While chemotherapy drugs affect all rapidly dividing cells and kill cancerous cells, targeted therapy drugs affect specific molecules within cells to block cell growth.

Monoclonal antibodies are the main type of targeted therapy drug used in Australia for advanced bowel cancer. They include:

• Bevacizumab – this drug stops the cancer developing new blood cells and growing. It is given as a drip into a vein every two to three weeks with chemotherapy.
• Cetuximab and panitumumab – these drugs target specific features of cancer cells known as epidermal growth factor receptors (EGFR). They only work for people who have a normal RAS gene. They are usually given as a drip into a vein, with chemotherapy or on their own after other chemotherapy drugs have stopped working.
• Encorafenib - this drug is used to treat a type of colorectal cancer with a mutation in the BRAF gene. It is given as tablets you swallow daily and used in combination with cetuximab. 

Scans and blood tests will be used to monitor your response to systemic treatments. If results show that the cancer is shrinking or is under control, chemotherapy and/or targeted therapy will continue. If the cancer is growing, that treatment will stop and alternative treatments will be discussed.

Common side effects of bevacizumab include high blood pressure, tiredness, bleeding and headaches. The most common side effects of cetuximab and panitumumab are tiredness, diarrhoea and skin problems including redness, swelling, an acne-like rash or dry, flaky skin.

Radiation therapy

Radiation therapy can be used as a palliative treatment for both advanced colon and advanced rectal cancer. It can be used to control the growth of the tumour and relieve symptoms such as bleeding. If the cancer has spread to the bone or formed a mass in the pelvis, radiation therapy can reduce pain.

If the tumour has spread to the liver, you may be offered a specialised type of radiation therapy. Options may include selective internal radiation therapy (SIRT) or stereotactic body radiation therapy (SBRT).

Immunotherapy 

Immunotherapy uses the body’s own immune system to fight cancer.  Checkpoint inhibitors are the main type of immunotherapy drug used for the small number of advanced bowel cancers that have a fault in the mismatch repair (MMR) gene. The drug pembrolizumab is given directly into a vein through a drip (infusion) and the treatment is repeated every 3 or 6 weeks. How many infusions you receive will depend on how you respond to the drug.

Side effects include rash, itchy skin, diarrhoea, breathing problems, inflammation of the liver, hormone changes and temporary arthritis. Your doctor will discuss possible side effects with you

Surgery

You may have surgery if bowel cancer has spread to the liver or lungs, or if the cancer blocks your bowel. Surgery may remove parts of the bowel along with all or part of other affected organs. This may be called an en-bloc resection or, if the cancer is in your pelvis, an exenteration.

If the cancer has spread to the lining of the abdomen (peritoneum), you may have surgery to remove as many tumours as possible. This is known as a peritonectomy or cytoreductive surgery. Sometimes, a heated chemotherapy solution is put into the abdomen during a peritonectomy. This is called hyperthermic intraperitoneal chemotherapy (HIPEC). Recent studies suggest that having surgery only may be as effective as surgery followed by HIPEC.

Thermal ablation

If the cancer cannot be removed with surgery but has spread to only a small number of places in a single area, your doctor may recommend thermal ablation. This uses heat to destroy the tumour. They are best performed in a specialised centre or may be offered as part of a clinical trial.