Long term side effects of anal cancer radiotherapy

Most side effects of radiotherapy to the anus gradually go away in the weeks or months after treatment. But some side effects can continue. Or you might notice some that begin months or years later. These are called long term side effects. 

Most of these side effects are rare. There are things you can do to help cope with the side effects. 

Talk to your doctor if you have developed any of these effects. It may be that your symptoms are due to something else, such as a bowel or bladder infection. If you have a side effect, your doctor or nurse can help manage your symptoms.

If you smoke, stopping before you start radiotherapy treatment is a good idea. It can help reduce the side effects caused by treatment and improve your general health.

Stopping smoking can be difficult, particularly when going through a stressful time. Talk to your doctor or nurse about support for stopping smoking.

Possible long term side effects

Frequent or loose poo

Your bowel movements might be looser or more frequent than before your treatment.

You might need to take anti diarrhoea medicines, such as loperamide (Imodium). Bulking agents, such as Fybogel, might also help. Your doctor or nurse can prescribe these for you. Talk to your doctor before taking these.

It’s usually best to try to have a healthy balanced diet if you can. Try to eat small meals and snacks regularly. Ask with your healthcare team if you need to make any changes to your diet. Some people find it best to avoid high fibre foods such as beans, nuts, seeds, dried fruit, bran and raw vegetables.

Drink plenty to try and replace the fluid lost. Aim for 8 to 10 glasses per day.

Let your doctor know if you have ongoing problems with frequent bowel movements or bleeding. They can refer you to a specialist team. The team includes:

  • cancer doctors
  • digestive system specialists
  • bowel surgeons
  • dietitians
  • specialist nurses

Difficulty controlling your bowels (faecal incontinence)

Radiotherapy may weaken the muscles in your anus. This can make it difficult to control your bowels (faecal incontinence). 

Talk to your doctors if you have problems controlling your bowels. They can refer you to a physiotherapist or community continence adviser for advice and information. You can also get details of your nearest continence clinic or an adviser from Bladder and Bowel UK. A continence adviser can also give you pads if you need them.

Doing regular pelvic floor exercises can also help. For example, you can practice holding on to your stool to build up the amount the bowel can hold. Your nurse, physiotherapist, or continence advisor can give you information about these.

'Just can’t wait' card

You can get a card if you want to go to the toilet more often, or feel that you can’t wait when you do want to go. You can show the card to staff in shops or pubs etc. It allows you to use their toilets, without them asking awkward questions. 

You can get the cards from Disability Rights UK or Bladder and Bowel UK. Disability Rights UK can also give you a key for disabled access toilets so that you don't have to ask for a key when you are out.

Bladder changes

Some people may have bladder changes, making:

  • the bladder wall less stretchy, so you have to pass urine more often
  • fragile blood vessels form in the bladder wall, causing blood in the urine
  • the tube through which urine passes out of the body narrower

Speak to your doctor if you are worried about any symptoms.

'Just can’t wait' card

You can get a card to show staff in shops or pubs. It allows you to use their toilets without them asking awkward questions. You can get the cards from Disability Rights UK or Bladder and Bowel UK.

Disability Rights UK can also give you a key for disabled access toilets so that you don't have to ask for a key when you are out.

Changes to your sex life

Changes to the sex organs may appear sometime after treatment. 

Men can have difficulty getting an erection.

Women may have dryness and shrinkage of the vagina, making sex painful. Using vaginal dilators after treatment can minimise this. Some women also have early menopause.

Both men and women might be unable to have children after treatment.

Talk to your doctor if you think you have developed any of these side effects. There are ways of reducing and managing them. 

Damage to your hip bones

Radiotherapy to the pelvis can damage the bones in the pelvic area. The bones can become weaker. This can cause pain and also increases the risk of fractures of the pelvis or hip.

Your doctor will monitor you carefully, including checking your bone strength with a DEXA scan. They might suggest treatment with painkillers and walking aids to help you get around, such as a stick. You might also need to take medicines to strengthen the bones called bisphosphonates. These drugs can help to control pain and reduce the risk of fractures.

Low levels of vitamin B12

You might have low vitamin B12 after radiotherapy to the pelvis (the area between your hip bones). This is called a vitamin B12 deficiency.

Radiotherapy can stop your digestive system from taking in (absorbing) vitamin B12 from the food you eat. This is called malabsorption. This means you can have a B12 deficiency even if you eat a balanced diet.

A B12 deficiency can be a cause of anaemia. This can lead to weakness, diarrhoea, numbness and tingling.

It’s important that you go to your doctor if you’re experiencing these symptoms so that they can help you.


Radiotherapy to the lower tummy (pelvis) and to lymph nodes such as the inguinal lymph nodes in the groin can cause scar tissue. This can interfere with the flow of lymph and cause a build up of fluid (swelling). This is called lymphoedema. Swelling may appear in the tummy area, genitals or legs.

Lymphoedema is a chronic condition that can be managed by a lymphoedema specialist. If you notice any swelling, speak to your doctor or specialist nurse. They can refer you to a lymphoedema service.

Pain in your back passage

Some people may have long term discomfort or pain in their back passage. Tell your doctor if you are struggling with these symptoms. They can suggest treatments that can bring relief.

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