If bowel cancer spreads to another part of the body it is called metastatic bowel cancer

With time, cells from the tumour can break off from the primary (original) tumour and enter the bloodstream or lymphatic system, spreading the cancer to nearby lymph nodes or other parts of the body. This may result in a separate tumour forming in another part of the body.

The liver is the most common site for bowel cancer cells to spread to because the blood supply to the bowel passes through the liver as it returns to the heart. The lungs are also a common site of metastases because of the high blood flow, which can carry cancerous cells from the bowel.

It is important to remember that metastases are formed by cancerous cells from the bowel growing in other organs, such as the liver or lungs. Therefore, the treatments used are specific to patients with bowel cancer and different to those used to treat lung cancer and liver cancer.

Treatment for metastatic bowel cancer

Bowel cancer may already be metastatic at the time of diagnosis, or metastases may appear after early-stage bowel cancer is detected and treated if all cancerous cells are not removed during surgery, or destroyed by chemotherapy.

Metastatic bowel cancer is treated differently to early-stage bowel cancer. In cases of metastatic bowel cancer, cancerous cells are no longer isolated to the bowel or the area immediately surrounding the tumour.

Two types of treatment may be offered:

• Medical treatment
• Surgical treatment

The choice of treatment depends on a number of factors including:

• The size and number of metastases and where they are in the body
• The type of bowel cancer you have, i.e. the type of cells, genetic markers in the tumour, etc.
• Any previous treatments for bowel cancer
• Patient factors, such as your age, general health, ability to tolerate treatment and personal preferences

Medical treatment of metastatic bowel cancer

Medical treatment for metastatic bowel cancer involves two main types of anticancer therapy:

• Chemotherapy – These drugs are designed to non-specifically destroy rapidly dividing cells, such as cancerous cells
• Targeted therapies – These drugs may be combined with chemotherapy and are designed to selectively target cancer cells and the mechanisms that encourage their growth. A biopsy of your tumour or metastases may be required to help your oncologist select the best targeted therapy for you.

Some treatments may be administered as pills or tablets at home, but other treatments will require you to attend a clinic to have your chemotherapy administered intravenously.

Medical treatment for metastatic cancer is considered to be palliative because it is unlikely to cure the cancer. However, treatment can help patients live longer by limiting the growth of any tumours (or shrinking them) and helping maintain quality of life by controlling symptoms.

Treatment can be associated with unpleasant side effects, which vary depending on the treatment option chosen by you and your oncologist. However, there are several medical treatment options available for patients with metastatic bowel cancer, so if you do not respond to one treatment, or find the side effects too difficult to tolerate, an alternative option may be available.

 How do you know if chemotherapy is working?

You will most likely have a computed tomography (CT) scan prior to starting chemotherapy, and another one to assess response to treatment at approximately 3 months. Any changes in tumour size between scans can give an indication of how well your treatment is working.

• If the tumour and metastases have become smaller, your oncologist may discuss continuing treatment or having a break.
• If the tumour has remained the same size, your oncologist may want to discuss your treatment and the pros and cons of continuing versus switching.
• If the tumour has become bigger, your oncologist may suggest trying a different treatment option.

Surgery for metastatic bowel cancer

Surgery can be used in some situations to treat metastatic bowel cancer:

• To remove the primary tumour in the bowel
• To remove or control metastases or local recurrence.

The primary tumour may be removed from the bowel, especially if it is at risk of causing complications if it is left in place, such as blocking the bowel or growing outside of the bowel, directly into other organs. Often the primary cancer can be managed without surgery, with a stent to keep the lumen of the bowel open, or if the tumour responds to chemotherapy, no operative treatment may be required.

Surgery to remove metastases, particularly in the liver, may also be possible, but this is dependent on a number of factors, such as the size and location of the metastases in the liver and the presence of metastases in other organs amongst other factors. In some cases, patients who are not candidates for surgery may become eligible if medical treatment sufficiently shrinks their tumours.

In highly selected cases reasonable survival can be expected (5-year survival: 35–45% with surgical removal of liver and lung metastases). However, for most patients metastatic disease is not resected and there are often cancer cells elsewhere in the body that are not easily seen on scans.

Surgery for a blocked bowel

Sometimes bowel cancer can grow to the point where it completely blocks the bowel.  This is called a bowel obstruction and can cause a number of symptoms, such as:

• Feeling bloated and full
• Pain
• Feeling sick
• Vomiting
• Constipation.

To relieve the symptoms of a blocked bowel the primary tumour may be surgically removed, or bypassed. However, this may result in a colostomy being required if it is not possible to completely repair the bowel following surgery.

Alternatively, it is sometimes possible to unblock the bowel by inserting a stent. A stent is a wire mesh that holds to bowel open, allowing the contents of your bowels to pass unimpeded. This can be performed by passing a collapsed stent into the bowel during a colonoscopy and expanding it once it reaches its desired location.