Ask The Doctor New Dna Based Test For Colorectal Cancer

Overview

Colorectal cancer is cancer that starts in the colon or the rectum, which are parts of your digestive system. A new DNA-based test looks at a sample of your stool (or sometimes blood) for tiny pieces of altered DNA that may be shed by cancer cells or pre-cancerous growths called polyps. This is a screening test, not a diagnosis. It helps find warning signs early, so you can have a follow-up test like a colonoscopy if needed.

Colorectal cancer is one of the most common cancers worldwide. Screening tests, including DNA-based tests, are becoming more widely available to help detect it earlier.

It affects both men and women. It is most common in people over 50, but it can happen at any age, and cases in younger adults have been rising in recent years.

Symptoms

Common symptoms

• Changes in bowel habits, such as diarrhoea or constipation lasting more than a few weeks
• Blood in or on your stool (poo)
• Abdominal pain, cramps, or bloating that does not go away
• Unexplained weight loss
• Feeling very tired all the time

Symptoms in children

• Colorectal cancer is very rare in children, and these tests are not used for children. If your child has concerning symptoms, such as persistent stomach pain or blood in their stool, see a paediatrician.

Symptoms in older adults

• The symptoms are the same as in the general population, but they may be mistaken for signs of ageing or other digestive conditions. Any persistent change in bowel habits or blood in the stool should be checked by a doctor.

Causes

Main causes

• Colorectal cancer often starts as abnormal growths called polyps on the inner lining of the colon or rectum. Over time, some polyps can become cancer.
• DNA changes (mutations) in the cells of the colon or rectum can cause them to grow out of control and form a tumour.

Risk factors

• Getting older, especially after age 50
• A family history of colorectal cancer or polyps
• Inflammatory bowel disease, such as Crohn's disease or ulcerative colitis
• A diet high in processed meats and low in fibre
• Smoking and heavy alcohol use
• Being overweight or not physically active
• Black or African ancestry – these groups have a higher risk in the UK

When to see a doctor

See a doctor urgently if:

• If you notice blood in your stool, changes in bowel habits that last more than a few weeks, or unexplained weight loss
• If you have severe belly pain and fever
• If you have a positive result from a DNA-based screening test – you should see a doctor promptly for follow-up

Book a routine appointment if:

• Talk to your doctor about colorectal cancer screening when you reach the recommended age (usually 45–50, depending on your local guidelines)
• If you have a family history of colorectal cancer, your doctor may recommend starting screening earlier

Diagnosis

If a screening test like a DNA-based test is positive, or if you have symptoms, your doctor will usually order a colonoscopy. During a colonoscopy, a thin, flexible tube with a camera is used to look at the entire colon and rectum. If any suspicious areas are found, small tissue samples (biopsies) are taken and checked under a microscope. Only a biopsy can confirm whether cancer is present.

Tests that may be done

• Stool DNA test (e.g., a multi-target stool DNA test, although we do not name brands)
• FIT (Faecal Immunochemical Test) – looks for hidden blood in the stool
• Colonoscopy – the gold standard for diagnosis and biopsy
• CT colonography (virtual colonoscopy) – a CT scan of the colon

What to expect at your appointment

Before a colonoscopy, you will be given instructions to follow a special liquid diet and take a laxative to completely empty your colon. You will usually be sedated during the procedure, so you will feel relaxed and remember little afterward. The test typically takes 15–30 minutes. You may have some bloating or mild cramping for a day, but most people return to normal activities the next day.

Treatment

Treatment for colorectal cancer depends on how far the cancer has spread (the stage) and your overall health. Surgery is often the main treatment, and it may be combined with other treatments to lower the risk of the cancer returning.

Self-care at home

• Attend all follow-up appointments and scans your doctor recommends
• Keep a record of any new symptoms and tell your care team
• Seek support for emotional or mental health concerns – it is normal to need help
• Ask your doctor before taking any over-the-counter medicines or supplements

Medical treatments

In addition to surgery, treatment may include chemotherapy (medicines that kill cancer cells), radiotherapy (high-energy X-rays to shrink or destroy cancer), and targeted therapy that attacks specific changes in cancer cells. Your cancer team will explain which treatments are appropriate for your situation and what the likely side effects are.

When is surgery considered?

Surgery is the most common treatment for colorectal cancer. It involves removing the part of the colon or rectum with the cancer, along with some healthy tissue around it. If the cancer is caught early, surgery alone can often be enough to cure it.

Living with this condition

After treatment, you may need time to recover and adjust. Some people experience bowel changes, such as more frequent stools or difficulty with digestion. These usually improve over time, but it is important to talk to your care team about anything that bothers you.

Lifestyle tips

• Take gentle walks to keep moving, but listen to your body and rest when needed
• Avoid smoking and limit alcohol
• Ask your care team before starting any new exercise routine
• Stay connected with family and friends – they can be a strong source of support

Diet and exercise

Eat a balanced diet rich in fruits, vegetables, whole grains, and lean proteins. Keep portions moderate and chew food well. After surgery, you may need to eat smaller, more frequent meals. If you have a stoma, a dietitian can help you adjust. Daily gentle exercise, such as walking or swimming, can improve energy and mood, but always follow your doctor's advice about activity levels.

Mental health and emotional wellbeing

A cancer diagnosis can bring feelings of fear, sadness, and anxiety. These emotions are completely normal. Many people find it helpful to talk to a counselor or psychologist who specialises in cancer care. Your care team can help you access these services.

Prevention

Not all colorectal cancers can be prevented, but you can lower your risk by keeping a healthy weight, staying physically active, eating plenty of fibre and vegetables, limiting red and processed meat, not smoking, and limiting alcohol. Regular screening is also key – it can find and remove polyps before they ever become cancer.

Screening programmes

Several types of screening tests are available, including stool-based tests like the DNA test, and visual tests like colonoscopy. Which test is right for you depends on your age, risk level, and local healthcare guidelines. Ask your doctor about what screening is recommended for you and when to start.

Complications

If left untreated

• The cancer can grow deeper into the bowel wall and spread to nearby lymph nodes
• It may travel to other organs, most often the liver or lungs, which makes treatment more difficult
• An untreated tumour can cause bowel blockage, which is a medical emergency
• Bleeding from the tumour can lead to anaemia (low red blood cells) and severe tiredness

Long-term outlook

Colorectal cancer has a very good outlook when found early. More than 9 out of 10 people with early-stage bowel cancer are alive five years after diagnosis. Newer DNA-based tests aim to help more people get screened, so the disease is caught sooner, when it is most treatable. Even if the cancer has spread, treatment options are improving all the time.

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