Photodynamic therapy (PDT) is an effective, licensed cancer treatment that should not be confused with the unproven, unlicensed versions of PDT sold by some private clinics in the UK and overseas.
PDT has been proven to treat a number of cancers and skin conditions, including early-stage lung cancer, oesophageal (gullet) cancer and Bowen's disease.
However, the so-called "advanced" versions of PDT, called "next-generation PDT" (NGPDT) and "sonodynamic therapy" (SDT), are not supported by scientific evidence.
Clinics promoting NGPDT and SDT have been criticised for falsely claiming that these alternative therapies can treat late-stage cancers.
If you or your child are seriously ill with cancer, it is understandable to feel desperate and want to try every available treatment that might help.
However, if you opt for NGPDT or SDT rather than following NHS advice or treatment, you could be putting your life at risk. Your condition may deteriorate further and you may experience unknown adverse effects from the therapy.
NGPDT and SDT are not even suitable as a last resort for incurable cancer. They may result in unnecessary pain and you may be faced with unaffordable costs, as the recent tragic story of Olivia Downie highlights (see box or watch the BBC documentary).
NGPDT and SDT are promoted by certain private clinics in the UK, Mexico and China which advertise the therapies on their websites. Medical experts critical of these clinics believe the people running them are misguided or fraudulent (see 'The claims', below). The treatment is very expensive, typically costing in the region of £10,000.
So, how is conventional PDT different?
Photodynamic therapy (PDT)
PDT is offered in some NHS hospitals and clinics, and is an effective treatment for certain cancers and conditions that may turn into cancer.
It involves taking a light-sensitive drug that is attracted to cancer cells and builds up inside them. You take this in the form of a drink, injection or a cream to rub into your skin, depending on the disease being treated.
After the drug has built up in the cancer cells, a red lamp or laser is shone onto the affected area of the body. The light activates the drug, which destroys the cancer cells by combining with oxygen to form a short-lasting substance that is toxic to the cells.
If PDT is being used to treat a skin condition, the laser will be shone directly onto the skin. For diseases deep inside the body, an endoscope (flexible tube) will be passed into the body to deliver the light to the tumour.
PDT can be highly effective for treating certain skin conditions and cancers near to or on the lining of internal organs. For example, the National Institute for Health and Clinical Excellence (NICE) has approved PDT for use in skin cancer and certain types of internal cancer where it is possible to get light from a laser to within a few millimetres of the tumour.
For early-stage cancers, the aim is to try to cure the cancer. For more advanced cancer, it can be used alongside other therapies to shrink the tumour and bring relief from symptoms, improving quality of life towards the end of a patient's life.
In summary, PDT is available in specialist NHS dermatology centres to treat skin diseases such as Bowen's disease, basal cell carcinoma and actinic keratosis (but not melanoma skin cancer).
In some circumstances, it may also be available for:
PDT shows promise in treating other cancers too, such as head and neck cancer, bile duct cancer, pancreatic cancer, prostate cancer, bladder cancer and brain tumours, although these uses are still undergoing clinical trials and more evidence is needed.
However, there are many cancers that PDT cannot treat, because the red light used for activating the PDT drugs can't penetrate deep enough.
Limitations of PDT
The light used in PDT can only have an effect through tissue at a depth of up to about 1cm.
This is why PDT is not effective in treating cancers deep inside the body that have spread to nearby lymph nodes.
Sadly, neuroblastoma (a rare cancer of the nervous system) is not susceptible to PDT because the cancer cells hide and invade parts of the body that light cannot reach.
In cases where cancer has spread to nearby lymph nodes, radiotherapy and surgery are the recommended treatments.
For cancers that have spread beyond the nearby lymph nodes, often the only treatment is chemotherapy.
NGPDT and SDT
Clinics in Mexico and China are promoting NGPDT and SDT as "advanced forms" of PDT.
They sell NGPDT and SDT as natural, non-invasive therapies that use non-toxic light-sensitive substances such as chlorophyll.
These clinics say that the drugs they use "explode" with oxygen, killing the cancer cells when they are activated not only by light, but also by ultrasound waves, which can apparently reach every part of the body.
They claim they can effectively treat deep or widespread cancers such as advanced liver cancer or neuroblastoma.
What reputable health experts say
Health experts believe that people running such clinics are either misguided or exploiting the vulnerable public for commercial gain.
None of the above claims are supported by scientific evidence, and stories such as Olivia Downie's reinforce the knowledge that SDT does not help treat neuroblastoma.
In fact, a 2010 critical appraisal of a clinical application of sonodynamic therapy concluded that:
"There is no convincing data that shows that ultrasound used in this way is effective in the treatment of primary tumours and multiple metastases [cancer that has spread]."
The authors question how the superficial light source used can reach the deep-seated cancers in lung and bone tissues. They rightly stress their concerns about the use of unproven interventions in terminally ill cancer patients.
Without information proving that these unconventional techniques and substances are safe and effective, it is unethical to offer them to patients – particularly those who are near the end of their life and very weak.
Support and information
Parents of children with terminal cancer may find the following organisations and information helpful:
Cancer Research UK: dying with cancer
Caring for a terminally ill child
Children in hospital
Macmillan Cancer Support: advanced cancer
Video: palliative care at home