Photodynamic therapy (PDT) is a treatment that uses a light-sensitive drug and a laser or light source to destroy cancer cells.
The drug is attracted to the cancer cells. But it does not become active in these cells until a light is shone on it. Using a certain light or laser will activate the drug to release a type of oxygen that kills the nearby cancer cells.
Some healthy, normal cells in the body will also be affected by PDT, but these cells usually recover after treatment.
PDT is not widely available around the UK, so you may have to travel to have it.
PDT can be used to treat some types of cancer. These include:
PDT can also be used when the cancer or affected area is on, or near, the lining of internal organs.
When PDT is used to treat early-stage cancers, the aim is to try to cure the cancer. PDT can sometimes be used to treat small, early lung cancers in people who can't have surgery.
When PDT is used for more advanced cancers, the aim is to shrink the cancer and reduce symptoms. It can sometimes be used to relieve breathlessness and improve swallowing in people with advanced cancer of the lung or the gullet (oesophagus).
Researchers are trying to find out which types of cancer PDT works best for. Clinical trials are looking at new light-sensitive drugs and new laser and non-laser light treatments. They are also trying to find ways of reducing the side effects. You may be offered PDT as part of a trial.
Your hospital doctor can tell you whether PDT is the right treatment in your situation.
Treating pre-cancerous conditions
PDT is also used to treat some pre-cancerous conditions, including:
- Barrett's oesophagus – where the cells of the oesophagus (gullet) grow abnormally
- Bowen's disease – where the cells in the outer layer of the skin grow abnormally
- actinic keratoses – scaly dry patches of skin caused by sun damage.
Some research studies have used PDT to treat pre-cancerous changes in the cells of the vagina, anus and vulva.
The treatment is normally given in two stages.
The first stage of treatment is when you are given the light sensitive drug. If you have skin cancer, the drug is usually applied to your skin as a cream. For cancers that are inside the body, the drug may be given as an injection into a vein (intravenously). Occasionally it is given as a drink.
Once you have had the drug, there is a delay before the second stage of treatment. This allows time for the drug to build up in the cancer cells. The time you wait after having the drug may be a few hours or a few days. This will depend on the type of cancer you have and its treatment. You will usually be able to go home during this time.
There are different types of light sensitive drug. The most common are:
- 5-aminolevulinic acid (5-ALA)
- temoporfin (Foscan®)
- porfimer sodium (Photofrin®).
The drug used will depend on the type of cancer you have and which is best for your situation. Your doctor or nurse will explain more about this and tell you how the drug is given.
The second stage of treatment involves shining a laser, or sometimes a non-laser, light on to the cancer or the affected area.
For treatment to the skin, the light is shone straight on to the skin. For cancers inside the body, a flexible tube (endoscope) may need to be passed into your body to guide the light to the affected area. A scan or ultrasound may be used to help direct the light to the right part of the body.
Sensitivity to light
The light sensitive drugs will mostly build up in the cancer cells. But normal cells can also be affected, so your skin and eyes may also become very sensitive to light. You will gradually become less sensitive to light and things will return to normal. The time this takes will depend on which drugs you had. Your hospital team will give you more information about your treatment. They will also give you advice on using lights inside your home, as well as other ways to avoid or reduce your exposure to strong lights.
Other side effects of PDT will be different for each person and depend on:
- the area of the body being treated
- the type of light sensitive drug
- the amount of time between the stages of treatment
- how sensitive your skin is to light after the treatment.