Photodynamic therapy (PDT)

PDT is a safe and effective non surgical method for the management of sunspots and certain superficial skin cancers such as actinic keratosis (AK), superficial basal cell carcinomas (SBCC less than 2mm thick), and Bowens disease (SCC in situ).

How does it work?

PDT involves the application of a cream (Metvix) to your skin cancer followed by light activation of the cream which results in the death of the skin cancer cells. Metvix is metabolized better by skin cancer cells than normal skin cells hence it removes your skin cancer without harming normal skin. When tumor cells absorb Metvix a chemical is generated within them (protoporphyrin IX) that becomes activated when a light of a specific wavelength is directed onto the area. This reaction kills the skin cancer cells.

PDT has been found to give cure rates of 85% to 90% for SBCC and Bowen’s disease (SCC in situ). PDT is not effective for BCC’s greater than 2mm in depth. A skin biopsy is often warranted prior to treating any lesion so as to confirm the diagnosis and to make sure the lesion is of correct thickness to respond to the treatment. Nodular BCC’s are less responsive to PDT, but in certain circumstances it may be reasonable to treat these lesions with PDT.

PDT for Actinic Keratosis

Actinic keratosis (sunspots) are pre cancerous lesions. Without treatment a significant proportion of these will develop into skin cancer (SCC or squamous cell carcinoma). SCC’s can be potentially life threatening skin cancers and usually require surgery to manage.

Sunspots rarely occur in isolation. The presence of one AK usually means that there are many more. Some AK’s are clearly visible, some may be less obvious to the human eye ie microscopic. Hence, to manage AK’s correctly a “field” treatment is often necessary. A “field” means a region of skin eg a nose, or a forehead, a cheek, or in some severe cases a full face.

There are many field treatments for the management of AK’s and these include 5 Flurouracil (Efudix), Imiquimoid (Aldara), Chemical peels, PDT and laser resurfacing. Each of these modalities has its pros and cons. In clinical trials the efficacy and the low risk of side effects of PDT have demonstrated a high patient preference for this modality [Photochem Photobiol. 2008 Jan 23]

One treatment with PDT is required for AK’s.
Review at one week and 4 months following treatment is necessary to ensure tolerance and effectiveness of treatment

PDT for SBCC and Bowens

SBCC and Bowens are superficial skin cancers- without treatment these slowly progress to become deeper lesions that require surgical excision. Managing these focuses on the tumour itself, rather than the “field”. Two treatments with PDT spaced apart by 1 to 4 weeks are required to manage these lesions.There are multiple treatment options for these lesions other than PDT including cryotherapy (double freeze ), flurouracil (efudix), imiquimoid (aldara). Studies indicate a much better complete response rate and cosmetic results at 12months for Bowen’s lesions compared to cryotherapy and efudix [Arch Dermatol. 2006 Jun;142(6):729-35]. Excellent outcome has also been demonstrated for SBCC [Eur J Dermatol. 2007 Sep-Oct;17(5):412-5].

Two treatments are required for these lesions spaced apart by one to four weeks.
Review at 4 months following treatment is necessary to ensure tolerance and effectiveness of treatment.

Procedure

• When you arrive at the rooms the margins of the tumor or the region to be treated will be mapped out. The doctor will gently scrape the top of the lesion to enhance the absorption of the cream into the tumor or to reduce the bulk of the tumor cells.
• Metvix is then applied to the region to be treated as well as a small peripheral rim of normal skin tissue.
• A dressing is then placed over the top of the lesion. This must not be removed as exposure to direct sunlight may influence the effectiveness of the cream. After a period of 3 hours you will return to the surgery. This time allows for the cream to be absorbed into the cancer cells. It is helpful if you take two paracetamol one hour prior to returning.
• A trained nurse will remove the dressing, wipe off the cream, place protective googles on you and will then place a lamp at a specific distance from the area to be treated.
• The red light is directed onto the area to be treated for 8mins.
• Some people experience pain during the procedure. This varies from person to person; some mild, some moderate. If pain is severe the treatment can be stopped, or cool water is sprayed onto the region. Rarely local anaesthetic is infiltrated.
• After the treatment, the area will be dressed and this will help to settle the discomfort. Some areas, especially on the face, can become swollen after treatment. If you have had treatment on the face, it is best to sleep propped up on 2-3 pillows on the night after PDT to help reduce swelling. The swelling normally subsides within a few days.
• The dressing should be kept in place for 24 hours, as the area remains sensitive to light during that time. Even indoor lighting can activate the photosensitizing ointment and sunscreen will not be protective.
• The treated area and some of the surrounding skin will be red for 1-2 weeks. Occasionally blisters can develop at the treatment site

What are the possible side effects of PDT?

• Burning/stinging sensation during treatment
• Swelling and redness, crusting , itchiness, peeling and blisters which last one week
• Skin infections
• Scarring is generally minimal (but can be moderate). Loss of pigmentation may occur sometimes and can be permanent.

Sun protection and sun avoidance can prevent the development of skin cancer. If you have developed one skin cancer there is a 40% risk of developing further skin cancers. Regular skin checks are important.