Colon and rectal cancer explained

Colon cancer and rectal cancer are two different types of cancer that begin in the bowel. They’re sometimes grouped together using the terms colorectal cancer or bowel cancer, although they’re each treated differently and can impact your body in different ways.

How the colon and rectum work

Your colon and rectum are part of your digestive system and together form your large intestine.

Your colon is about 1.5m long and its job is to absorb water, vitamins and minerals from your digested food. Once this is done, the waste material (your stools) passes into your rectum. Your rectum is the final part of your large intestine and is about 15cm long. It holds your stools until they’re ready to pass through your anus when you have a bowel movement.

Cancer in your colon or rectum starts when cells that line the large intestine begin to grow abnormally. It often starts from polyps (small growths), although most polyps are harmless.

Bowel cancer is the fourth most common cancer in the UK, with about 40,000 cases each year.

What are the symptoms of bowel cancer?

Colon cancer and rectal cancer share some of the same symptoms. These include:

• A change in your bowel habits, such as going to the toilet more often or having persistently looser, runnier stools
• Blood in your stool that isn’t caused by haemorrhoids or anal fissures
• Pain, bloating or discomfort in your abdomen after eating

It’s important to remember that in most cases having these symptoms does not mean that you have bowel cancer. However, if you get any of these symptoms persistently, you should see your doctor.

What are the risk factors for bowel cancer?

Just over half of cases of bowel cancer are preventable and many cases are linked to diet. According to Cancer Research UK, almost one in three cases are caused by not eating enough fibre and over one in 10 cases are caused by eating red meat and processed meat.

Other risk factors include:

• Being overweight
• Drinking alcohol
• Having a family history of bowel cancer
• Not getting enough exercise
• Smoking
• Your age — nine in 10 people who develop bowel cancer are over the age of 60

Getting diagnosed

As colon cancer and rectal cancer both affect the large intestine, they are diagnosed using the same types of tests.

The first step involves a blood test and a physical examination. Your doctor will feel your abdomen and rectum to detect any lumps.

If your doctor thinks you might have bowel cancer, they will refer you for further tests. These can include:

• Colonoscopy — a tube with a camera and a light on the end is carefully passed through your rectum, enabling your doctor to see inside your bowel; if any abnormal tissue is found during the examination a sample (biopsy) may be taken to check if it is cancerous
• Flexible sigmoidoscopy — this is similar to a colonoscopy, but a shorter tube is used
• Virtual colonoscopy — this is non-invasive and uses a CT scan to create images of your bowel

If your tests show that you have bowel cancer, you’ll need to have further tests so that your doctor can determine what stage your cancer is at and if it has spread to any other parts of your body. These tests can include a CT scan, an MRI scan, a PET-CT scan or an ultrasound scan.

A CT scan is similar to an X-ray but produces more detailed images by using specialised X-rays and a computer. 

An MRI scan uses radio waves and magnets to create detailed images.

Before having a PET–CT scan, a special type of sugar (radioactive glucose) is injected into your body, which during your scan helps show your doctor if you have any abnormal growths. Cancerous cells use glucose at a much faster rate than normal cells, so a high concentration of this sugar in a particular area can suggest cancer.

During an ultrasound scan, a small handheld device is moved across your body. This device emits sound waves and the echoes that bounce back from your tissue are used to create an image on a computer.

The difference between colon cancer and rectal cancer

Colon cancer and rectal cancer affect different parts of your large intestine. As the names suggest, colon cancer starts in your colon and rectal cancer starts in your rectum.

Most of the length of your colon sits between your ribcage and your pelvis and doesn’t have other organs nearby. Your rectum, on the other hand, is lower down and is surrounded by other organs, such as your bladder, prostate (in men) and womb and vagina (in women).

Your colon has a protective outer layer called the serosa. The serosa only covers a small part of your rectum. As your rectum is surrounded by other organs and it doesn't have the same protective layer as your colon, rectal cancer is more likely to spread to other parts of your body. It also means that rectal cancer is more likely to return after treatment.

Treatment

Due to the different locations and differences in how each type of cancer can spread, colon cancer and rectal cancer are often treated differently.

Colon cancer treatment

If you develop colon cancer you’ll usually have surgery. The cancerous tissue, the colon tissue either side of it, and any nearby lymph nodes are usually removed. Lymph nodes are removed because if cancer spreads to them, it can then spread to other parts of your body. Once the cancer is removed, your surgeon will repair your colon.

A colostomy (an opening through which your stools are removed from your body) is not normally needed after surgery for colon cancer. If it is, it’s usually only for a short time. 

Rectal cancer treatment

Surgery for rectal cancer can be more complicated than surgery for colon cancer because of the organs that surround your rectum. Radiotherapy and chemotherapy are sometimes used before surgery to try to reduce the amount of cancerous tissue that needs to be removed by surgery.

If your cancer is at a later stage, the surgery needed to remove it often means you’ll need a colostomy for the rest of your life. Your doctor will explain how a colostomy works and how best to take care of it.

Sometimes rectal cancer will have spread to other organs. In these cases, your surgeon might need to remove your rectum and other organs that are affected, such as your bladder or prostate. If your bladder has to be taken out, you will need a urostomy (an opening through which urine is removed from your body).