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What is Colorectal Cancer?

Colorectal cancer (cancer of the bowel, colon or rectum) is the fourth most common cancer in the UK according to the British Medical Journal. For females, it’s the third most common. Each day, around 120 people are diagnosed with bowel cancer and 11% of all new cancer cases are in this category.

There are more than 42,000 cases of colorectal cancer diagnosed every year in the UK with a five-year survival rate of almost 60%. The 10-year survival rate is also high, at about 53% according to Cancer Research UK. Despite this, 16,808 people died from bowel cancer between 2017 and 2019. It’s also the second most common cause of cancer death, with 10% of cancer deaths attributed to it.

Shockingly, 1 in 15 males and 1 in 18 females will be diagnosed with bowel cancer in their lifetime. With 54% of bowel cancer being preventable, it’s really important that we find out a little more about the disease and especially how it can be prevented and treated.

What is colorectal cancer?

Colorectal cancer is cancer that starts in the colon (colo) or the rectum (rectal). Sometimes, colorectal cancer is called colon cancer, bowel cancer or rectal cancer, depending on where it starts. They are grouped together as colorectal cancers because they are largely very similar in their features.

Firstly, it’s important to know exactly where and what the colon and rectum are as it helps us to understand the development of colorectal cancer. The colon and the rectum are the parts of the digestive system that make up the large intestine. Most of the large intestine is the colon, and it measures about 1.5 metres in length.

There are four sections to the colon:

  • The ascending colon – This is the first section, and it starts with a pouch-like shape at the end of the small intestine called the caecum. It goes up the body (ascends) to the right side of the abdomen.
  • The transverse colon – This is the section of the colon that travels across the body from right to left in the abdomen.
  • The descending colon – This is the section of the colon that travels down (descends) the body on the left-hand side.
  • The sigmoid colon – This is the final section of the colon, called the sigmoid colon because it has an “S” shape. The sigmoid colon goes to the rectum, which then connects to the anus.

Sometimes, you may hear someone talk about the proximal colon and the distal colon. The proximal colon refers to the ascending and transverse colon as a pair, and the distal colon is the descending and sigmoid sections of the colon grouped together. The rectum is the final 15 centimetres of the digestive system, where faeces is stored until it is passed in a bowel movement.

Colorectal cancer is any cancer that develops in any of these parts of the digestive system.

However, there are different types of cancers that develop here including:

  • Adenocarcinomas.
  • Carcinoid tumours.
  • Gastrointestinal stromal tumours (GISTs).
  • Lymphomas.
  • Sarcomas.

Most colorectal cancers are adenocarcinomas. These are cancers that begin in the cells of the colon or rectum that make mucus to lubricate it. Most of the time, when doctors talk about colorectal cancer, it is this kind of cancer that they are referring to.

There are some subtypes of this cancer, including mucinous adenocarcinoma or signet ring adenocarcinoma, and these may have a worse prognosis in comparison with other adenocarcinomas.

The other types of cancers that start in the colon and rectum are much less common. Carcinoid tumours start from cells in the intestine that make hormones. GISTs start from cells in the walls of the colon, called interstitial cells of Cajal. Sometimes, these are non-cancerous tumours (benign), and they can occur anywhere in the digestive tract, not just the colon and rectum. They tend not to be common in the colon.

Lymphomas (cancers of the immune system cells called lymphocytes) can also start in the colon and rectum, but they most often start in the lymph nodes. Sarcomas start in muscle layers, blood vessels and connective tissues in the colon and rectum. However, these are rare.

Cancer beginning in lymph nodes

What are the signs and symptoms of colorectal cancer?

Colorectal cancer can have many or few symptoms. For some people, such as the actress Kirstie Alley who died of colorectal cancer in December 2022, the cancer has been referred to as “the silent killer”. Dame Deborah James, affectionally known as Bowel Babe, also succumbed to the disease in June 2022 after being diagnosed with Stage 4 bowel cancer in 2016. It was part of Deborah’s legacy that people are more informed of the signs and symptoms of bowel cancer so that it can be caught early and treated.

According to research by Bowel Cancer UK, almost half of adults in the UK cannot name a single symptom of the disease.

Bowel Research UK campaign tirelessly to help raise awareness of the symptoms and has come up with the following to help remember:

  • B – Bleeding from your bottom.
  • C – Change in normal bowel habits that lasts for more than three weeks.
  • A – Abdominal pain, acute tiredness, and/or a lump in your tummy.

However, there are also a few other symptoms to consider such as unexplained weight loss, a feeling that you have not emptied your bowel properly after you poo, and feeling breathless or tired, which could be due to lower levels of red blood cells. Some people also have pain in the rectum.

Blood in your poo is an important sign and any bleeding that you notice should be reported to your doctor. Quite often, blood can be caused by other factors such as haemorrhoids, but you won’t know this until you have it investigated. Bright red, fresh blood is often associated with haemorrhoids (commonly called piles) as these are fragile veins that have become swollen in the rectum.

Blood that comes from higher in the bowel is mostly not quite as bright red as blood from haemorrhoids. It looks dark red or sometimes even black and poo can resemble tar. Of course, even though it is alarming, it’s not always caused by cancer either and could be from a stomach ulcer, for example.

What causes colorectal cancer?

Having stated that 54% of colorectal cancers are preventable, it’s important to know the causes of such cancers in order to be able to try and prevent them or at least reduce the risk of them developing.

The development of colorectal cancer isn’t generally triggered by one single thing. Usually, a combination of factors is at play. However, whatever the trigger, colorectal cancer happens when the cells in the bowel or rectum divide and multiply too quickly, producing a “lump” called a tumour. Most of the time, bowel cancer begins inside polyps within the bowel’s inner lining.

Polyps are little growths inside the lining of the colon and rectum. They are very common and 1 in 4 over-50s have polyps, with slightly more men having them than women.

Many people just have a single polyp, but others may develop more than one. The polyps themselves often do not cause symptoms, so even if you have them, you might not be aware of it. However, larger polyps can cause an increase in bowel mucus or blood in the poo, constipation or diarrhoea, and abdominal pain.

Most of the time, polyps do not turn into cancer, but there are some types called adenomas that sometimes do turn into adenocarcinomas and so should be removed. No one really knows what causes bowel polyps, but it could be that the body produces too many cells within the bowel lining and these cluster into a “bump”. They’re usually only discovered if a person is having bowel screening for another reason.

What are the risk factors of colorectal cancer?

As mentioned, having some types of polyps is a risk factor for developing colorectal cancer. In fact, doctors believe that nearly all bowel cancers start off in adenoma polyps. However, it takes many years for this to happen. If a person is diagnosed with polyps, they will be monitored regularly to ensure that they are treated.

Polyps are usually removed during a colonoscopy procedure where a camera in a flexible tube is inserted through the anus and into the colon. The polyps are then cauterised or cut off (snared) by a special instrument. Both of these treatments are not painful. Sometimes, surgery is needed if there are lots of polyps or if the polyp is very large.

The polyps are then analysed in a laboratory to check for changes and to see if the whole polyp has been removed successfully.

Some people are more at risk of developing polyps and subsequently they are more at risk of developing colorectal cancers.

Risk factors for colorectal cancers include:

  • Age.
  • A close relative who has had polyps or has been diagnosed with bowel cancer.
  • Having an inflammatory bowel disease such as colitis or Crohn’s disease.
  • Being overweight.
  • Diet.
  • Genetic conditions.
  • Smoking.
  • Alcohol.
  • Inactivity.


Given that more than 90% of colorectal cancers are diagnosed in people over 50, the older a person is, the more at risk they are of developing colorectal cancer. Indeed, nearly 60% of colorectal cancers are in those of 70 years of age.

Family History

If someone in your family has been diagnosed with bowel cancer, unfortunately this means that your risk has increased, particularly if this was a first-degree relative such as a parent or sibling and they were under 50 at the time they were diagnosed.

You can speak to a GP if you are concerned about your family history, and they can refer you to a genetic specialist. The specialists can work out your personal levels of risk and offer advice and screening as necessary.

Digestive Disorders

Someone with Crohn’s disease or ulcerative colitis is at an increased risk of developing bowel cancer, particularly if they have had the disorder for over 10 years. Normally, those with these conditions have regular check-ups that will help to identify any changes in their condition and will look for bowel cancers developing. Check-ups are often done via a colonoscopy where a camera inside a flexible tube is inserted into the bowel via the anus.

Being Overweight

Being obese or overweight is associated with an increased risk of bowel cancer, particularly in men. Losing weight helps to lower this risk, as well as lower the risk of other diseases and conditions.


Lots of research has gone into the link between diet and colorectal cancer. Lots of the evidence suggests that there is a link between eating a diet that is high in processed and red meat and bowel cancer.

This is the reason why the Department of Health recommends that people should only eat 70g of processed or red meat each day. The evidence also suggests that fibre-rich diets help to reduce the risks of bowel cancers.

Genetic Conditions

There are two conditions that are inherited that put someone at an increased risk of bowel cancer:

  • Familial Adenomatous Polyposis (FAP)
    This is a condition that causes non-cancerous polyps to grow within the lining of the bowel. However, given that most causes of colorectal cancer are from polyps, this increases the person’s risk of developing colorectal cancer at some stage. Most people who have FAP will have colorectal cancer before they reach 50 years of age. Because of this risk, many people with the condition have their large bowel removed before they are 25.
  • Hereditary Non-Polyposis Colorectal Cancer (HNPCC) – Lynch Syndrome
    This is an inherited gene mutation which increases a person’s risk of developing colorectal cancer. Because the risk is so high, most people with Lynch Syndrome have their bowel removed as a precautionary measure.


Smokers are more likely to develop colorectal cancer (as well as other types of cancer and other serious conditions such as heart disease) due to the chemicals and toxins that enter the body when smoking.


Drinking alcohol also increases a person’s risk of colorectal cancer, particularly if you drink in excess regularly.


Being physically inactive and having a sedentary lifestyle puts someone at a higher risk of developing colorectal cancer.

Age affects risks of colorectal cancer

Can colorectal cancer be prevented?

The statistics speak for themselves. According to Cancer Research, 54% of colorectal cancer cases in the UK are preventable.

They go on to detail the percentages caused by certain risk factors:

  • 28% of cases are caused by eating too little fibre in the diet.
  • 13% of cases are caused by eating processed meat.
  • 11% of cases are caused by being overweight or obese.
  • 7% of cases are caused by smoking.
  • 6% of cases are caused by alcohol.
  • 5% of cases are caused by inactivity.
  • 2% of cases are caused by ionising radiation.

Of course, not all cases of colorectal cancer can be prevented, but you can reduce your risk by maintaining a healthy, fibre-rich diet, staying in shape and not drinking alcohol or smoking. Those with genetic conditions that lead to colorectal cancers can have preventative treatment where their colon is removed to stop them from developing the disease later in their life.

What are the stages of colorectal cancer?

The staging of colorectal cancer tells you how advanced the cancer is and whether it has spread to other parts of the body. The cancer is staged using numbers and the Tumour, Node and Metastasis (TNM) staging system.

The grading tells doctors how much the cancer cells resemble normal cells, which tells them how the cancer might behave and how it may respond to different treatments.


Colorectal cancers are graded as either “low grade”, which means they grow slowly, or “high grade”, which means they are quicker at growing.

Low Grade

  • Grade 1 – Well-differentiated cells, that look almost like normal cells.
  • Grade 2 – Moderately differentiated where cells look a little like normal cells.

High Grade

  • Grade 3 – Cells that are poorly differentiated and look very abnormal.
  • Grade 4 – Undifferentiated where the cells look completely different from normal cells.


Like most cancer diagnoses, colorectal cancer is diagnosed at a stage.

  • Stage 1 – Cancer has grown beyond the inner lining of the colon and into the muscle layer.
  • Stage 2 – Cancer has spread to the outer wall of the colon or into organs or tissue next to the bowel. There are no lymph nodes affected or other organs.
  • Stage 3 – Cancer has spread to the lymph nodes but not distant organs.
  • Stage 4 – Cancer has spread to other organs or parts of the body. This is the most advanced stage and is often referred to as “advanced bowel cancer”.

TNM Staging

This is one of the staging systems used to help differentiate how advanced the colorectal cancer is. It is more specific than the grading and staging systems already described.

The T stands for “tumour”:

Tis means carcinoma in situ (Tumour in situ). This means that the cancer is in its very early stages and is only in the mucosa of the bowel.

T1 means the tumour is in the inner layer of the bowel only.

T2 means the tumour has spread into the bowel wall’s muscle layer.

T3 means the tumour has spread to the bowel wall outer lining but has not grown through it.

T4 is separated into T4a and T4b.

  • T4a means that the tumour has passed through the outer lining of the bowel wall and has grown into the peritoneum – the tissue layer that covers the organs in the abdomen.
  • T4b means that the tier has grown through the wall of the bowel and into organs nearby.

The N stands for Node and describes whether the cancer has spread into the lymph nodes:

N0 means no lymph nodes have been affected.

N1 is split into three stages:

  • N1a – Cancer cells are in one lymph node nearby.
  • N1b – Cancer cells are in two or three lymph nodes nearby.
  • N1c – Cancer cells have not been found in nearby lymph nodes but there are cancer cells in the surrounding tissues near the tumour.

N2 is also split into stages:

  • N2a – Cancer cells are present in four to six nearby lymph nodes.
  • N2b – Cancer cells have been found in more than seven lymph nodes.

The M stands for Metastasis, which is the process that cancer goes through when it spreads to other parts of the body.

There are two stages of metastasis:

M0 – The cancer hasn’t spread to other parts of the body.

M1 – The cancer has spread to other parts of the body such as the liver or lungs.

There are three stages of M1:

  • M1a – The cancer has spread to one organ or distant site, such as the liver, but it hasn’t spread to the peritoneum (the tissue lining the abdomen).
  • M1b – The cancer has spread to two or more organs or distant sites, such as the lungs and liver, but has not spread to the peritoneum.
  • M1c – The cancer might have spread to other organs, and it has spread to the peritoneum.

This means that a person could be given a TNM grading of T3N1aM0 for example.

Can colorectal cancer be detected early?

Colorectal cancer is often detected early through screening. The screening programmes aim to detect changes in the bowel that could lead to cancer or detect cancer in its early stages. For people who take part, a screening kit is sent to them every two years. The test is called a FIT test which stands for Faecal Immunochemical Test.

The FIT test looks for minuscule traces of blood in the poo sample. The test is done at home and a pre-paid envelope is provided. Screening tests are not always perfect but if they identify some cases of cancer that would otherwise have gone undetected then they are an important service.

Many people prefer doing screening at home as they feel that their embarrassment is reduced. However, destigmatising talking about our bowel habits should definitely be a priority!

The results from the screening are sent by letter about two weeks later. Most people receive a letter that states “no further testing needed at this time”. It does not mean that the person definitely does not have cancer, but that nothing untoward has been detected. Of course, any unusual symptoms should still always be reported to your GP.

Others receive a letter that states they need further testing, and this means that blood was found in the sample provided. This does not mean that the person has cancer as blood in the poo can be there for other reasons. However, it is important that the test is followed up, as if it is cancer, detecting it early is really important.


How is colorectal cancer diagnosed?

If someone has had a change in their bowel habits or another of the signs or symptoms of possible colorectal cancer, their GP may perform further tests and refer them for further care.

These tests may include:

  • A rectal examination.
  • FIT test.
  • Flexible sigmoidoscopy.
  • Colonoscopy.
  • Colon capsule endoscopy.
  • CT colonography.
  • Blood tests.
  • CT scan.
  • MRI scan.
  • PET-CT scan.
  • Ultrasound scan of the rectum and/or abdomen.

Some of these tests may show that a person has a tumour located in their colon or rectum. If this is the case, usually a biopsy is taken from the tumour which is then analysed to show what type and/or grade the cancer is. Further tests may also be carried out to see what stage the cancer is and whether it has spread.

How is colorectal cancer treated?

Colorectal cancer is most often treated with surgery which might be combined with radiotherapy, chemotherapy or biological treatments depending on the type and stage of the cancer. If the cancer is detected early, the treatments should stop it from coming back.

However, sometimes curing it completely is not possible and, for many people, there will always remain the risk that it will recur. In more advanced cases of colorectal cancer, curing it is very unlikely, especially if removing it all by surgery is not possible. However, it can be slowed down and the symptoms can be minimised by treatments.


If the cancer was detected early enough, the cancer can be excised locally. This means that the area where the cancer is located is removed. However, if the cancer has spread to the muscles surrounding the colon, then a section of the colon needs to be removed. This is called a colectomy.

There are three ways of performing a colectomy:

  • A laparoscopic colectomy – Where there are a few small incisions where instruments and a camera are inserted into the abdomen. This is also known as keyhole surgery.
  • An open colectomy – Where a larger incision is made into the abdomen to gain access to the colon to remove the section needed.
  • Robotic surgery – A type of surgery where instruments are guided by a robot via a few small incisions in the abdomen. During this type of surgery, the surgeon does not touch the patient directly. This also means that the surgeon could be in a different hospital to the patient yet still perform the treatment. This is not yet available in many parts of the UK.

During surgery, the surgeons usually remove some of the nearby lymph nodes so that they can be examined. The remaining ends of the colon are then joined together. However, for some people this is not possible and so a stoma is also created.

The risks of both laparoscopic and open colectomies are reportedly very similar, but the former has an improved recovery time and so this way is becoming the standard procedure.

For rectal cancer, the surgery is often slightly different. Local resection is not usually possible as a larger area needs to be removed. This operation is called a total mesenteric excision (TME). The mesentery is the fatty tissue from around the bowel and removing it helps make sure all the cancer cells are removed to reduce the risk of it coming back.

If a stoma is needed, it may be an ileostomy (where the stoma is made from the ileum – the small bowel) or a colostomy (where it is made from the colon). For some people, the stoma surgery is reversible, but for others, they are fitted with a permanent stoma.


Radiotherapy is used to treat colorectal cancer before surgery, instead of surgery or as a form of palliative care. Before surgery, it shrinks cancers to make removing them easier. It can be used to cure early-stage disease, particularly in rectal cancers. Palliative radiotherapy aims to control a person’s symptoms and the spread of their disease to help extend their life.

Radiotherapy for rectal cancer can be external or internal (brachytherapy). External radiotherapy is usually given for five days a week over the course of one to five weeks depending on the size of the tumour. The sessions only last for about 10 to 15 minutes.


Chemotherapy is used for the same three reasons: before surgery to shrink a tumour often in combination with radiotherapy; after surgery to reduce the risk of it coming back; and as a palliative treatment to control the symptoms and slow the spread of the disease.

Chemotherapy is usually a combination of medicines that kill cancer cells. It can be in tablet form, intravenous form, or a combination of both. The treatment is given in cycles that are about two to three weeks long, depending on how advanced the cancer is or what grade it is. Sometimes, a course of chemotherapy lasts for six months.

Targeted therapies

These are biological therapies that target one or more of the biological processes that cause bowel cancers to spread throughout the body. For example, Panitumumab and Cetuximab are both medicines that target EGFRs – epidermal growth factor receptors – that are found on the surface of many cancer cells.

The EGFRs help cancer to grow and so targeting those cells can shrink cancers and improve how effective chemotherapy treatment is.

Final thoughts on “What is Colorectal Cancer?”

Colorectal cancer is any cancer that has grown in the colon or rectum. Fortunately, with advanced and improving treatments, many colorectal cancers are very treatable and curable. However, early detection and being aware of the signs and symptoms of the disease are crucial, as is reducing the embarrassment of the general population when talking about all things bowel related.

What is most important is knowing what’s normal for you and acting if anything changes.

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About the author

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Laura Allan

Laura is a former Modern Foreign Languages teacher who now works as a writer and translator. She is also acting Chair of Governors at her children’s primary school. Outside of work, Laura enjoys running and performing in amateur productions.

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