Early detection of bowel cancer: why it matters, what’s involved and signs to spot

Bowel cancer is the fourth most common cancer in the UK and in most cases affects the large bowel (colon) — cancer of the small bowel (small intestines) is extremely rare. According to Cancer Research UK, over half of all cases are preventable. This is in part because of several lifestyle factors that are known to increase your risk of bowel cancer, as well as screening, which can detect precancerous growths for removal. 

Risk factors for bowel cancer

Around one in 15 men and one in 18 women in the UK will develop bowel cancer during their lifetime. Risk factors include being overweight or obese, smoking, drinking alcohol, eating lots of processed meat and having an inactive lifestyle. However, the two biggest risk factors for bowel cancer are age and having a family history of the disease. 

Consequently, in England, everyone aged 60–74 is sent a bowel cancer screening kit every two years as part of the NHS National Bowel Cancer Screening programme — this is being extended to include those aged 56 and over. 

Bowel cancer screening

Screening involves sending off a sample of your stools to the NHS where it will be tested for microscopic traces of blood — this is a symptom of bowel cancer and pre-cancerous growths called polyps. This test helps detect bowel cancer in its earlier stages, which improves the chances of successful treatment.

Currently, the National Bowel Cancer Screening programme detects 75% of bowel cancer cases. Although screening is, therefore, very effective, it does mean that a negative result doesn’t completely rule out the presence of bowel cancer. Instead, a negative result means that provided you do not have any symptoms of bowel cancer, you are currently not in a high-risk group.

Stages of bowel cancer

Bowel cancer can be described according to its stages of progression. There are several different ways to classify the stages of bowel cancer but two that are commonly used in the UK — the TNM system and Duke’s classification.

The TNM system is based on how far a tumour has spread. The T refers to whether the tumour has grown through the bowel wall and is divided into T1–T4. The N refers to whether the cancer has spread to nearby lymph nodes and is divided into N0–N2. The M refers to whether the cancer has spread to other parts of the body (metastasised) and is divided into M0 or M1. This system helps doctors determine the best course of treatment ie surgery, chemotherapy, radiotherapy or a combination of these treatments.

Duke’s classification, which runs from A to D, is often more useful for patients as there is strong evidence for how each of these classifications relates to a patient’s five-year survival rate. Patients with bowel cancer classified as Duke’s A have a 90% chance of surviving five years or more. The subsequent groups have lower chances: Duke’s B has an 80% chance, Duke’s C has a 70% chance and Duke’s D has a 10% chance.

How do bowel cancer stages affect treatment?

Bowel cancer is one of the most treatable types of cancer. The earlier bowel cancer is picked up, the more likely treatment will be successful.

Patients may come in for a procedure called a colonoscopy to investigate symptoms that are not caused by bowel cancer and incidentally polyps may be discovered. As mentioned, polyps are not cancerous but can develop into bowel cancer. Removing them during a colonoscopy prevents bowel cancer developing and means no further treatment is needed. 

In cases where bowel cancer is only picked up after the tumour has invaded the bowel wall, surgery to remove the cancer followed by regular check-ups to monitor your bowel (surveillance) can be enough to prevent the cancer spreading or returning. 

As bowel cancer progresses, more involved treatment is needed, such as surgery followed by chemotherapy and/or radiotherapy. In these cases, the chances of the cancer spreading and/or returning are higher.

Detecting early bowel cancer symptoms

Before bowel cancer develops, there is usually a long period of time where precancerous polyps are present. If you have polyps you may experience episodes of bleeding from your back passage (rectum). However, you may only experience this once and in the vast majority of people with polyps, there are no symptoms at all. This makes it difficult to prevent bowel cancer from developing in the first place but is also a reason to see your GP as soon as possible if you experience even one episode of rectal bleeding, however minor it may seem. 

Once bowel cancer is present, traditional symptoms include rectal bleeding, a change in your bowel habits, unexplained weight loss and abdominal pain. You may also experience symptoms of iron-deficiency anaemia ie weakness, fatigue and a reduced ability to exercise. If you have any of these symptoms, you should see your GP as soon as possible.

Getting a diagnosis of bowel cancer

Whether you go to your GP with symptoms of bowel cancer, or get a positive result from the National Bowel Cancer Screening programme, you will be referred to have a colonoscopy, a type of endoscopy. It is worth noting that around 10% of people who receive a positive result from their bowel cancer screening, will actually have bowel cancer, while around 50% will have pre-cancerous polyps that need to be removed. 

During your colonoscopy, a thin, telescope-like tube with a camera and light on the end (a colonoscope) will be passed through your anus and up into your large bowel. Before your colonoscopy, you will need to drink a liquid laxative to clear out your bowel, so that your doctor can clearly see the inside of your bowel during your procedure. 

If your doctor detects any polyps, these can be removed during your colonoscopy. 

What happens after your diagnosis?

If bowel cancer is detected, surgery and surveillance will usually be recommended. However, depending on the position and stage of your bowel cancer, you may also need pre-surgery chemotherapy and radiotherapy to shrink the tumour and post-surgery chemotherapy and radiotherapy to destroy any cancer cells that were not removed during surgery.