By Gregory J. Wilmoth, M.D. of Southern Dermatology & Skin Cancer Center
PDT, otherwise known as photodynamic therapy, is a treatment that uses special drugs in conjunction with light to kill precancerous skin cells. These special drugs, or photosensitizing agents, are activated by certain kinds of light. Depending on where the treatment area is located, the drug may be applied to the skin or put into the bloodstream through a vein. Once the light is applied, the drug begins to react with oxygen, forming the cell-killing chemical.
Types of Cancer Treated with PDT
For the skin, the FDA has approved the photosensitizing agent Aminolevulinic acid, or ALA, to treat actinic keratosis (AK) – a skin condition that can become cancer – only on the face or scalp. A special blue light is used, instead of a normal laser, to activate this drug.
A derivative of ALA, Methyl ester of ALA, has also been developed to treat AK. A disadvantage of the older ALA drugs is that they do not enter into the cancer cells as easily. Newer ester forms, like methyl ester, do. Methyl ester is activated with a red light.
Light Sources Available
PDT light sources include laser light, intense pulsed light, LED lights, blue light, red light, natural sunshine and other visible light sources. Photosensitizing agents may be activated by more than one light source. The best light source depends on the ideal wavelength for the drug used and the tissue being targeted.
Pros and Cons of PDT Treatment
Studies have shown that PDT can treat cancer as well as surgery or radiation therapy in treating certain types of cancer and pre-cancers, like actinic keratosis. Some advantages are:
- No long-term side effects when performed by a trained doctor
- Less downtime compared to other treatments for AK, weeks of cream versus 7-10 days from PDT
- Precise targeting of precancerous cells
- Most often done as an outpatient treatment
- Little to no scarring
- Less costly than other precancer treatments
- Can treat wide areas of the skin all at once, such as the entire face
But, there are limits to what PDT can treat. These drawbacks are:
- PDT’s reach, it currently can only be used to treat problems on or just under the skin or in the lining of organs that can be reached with a light source
- PDT cannot be used to treat true cancers of the skin
- PDT leaves patients sensitive to light, meaning special precautions must be taken for patient comfort and safety
- PDT can’t be used in people with certain blood diseases
Patient Sensitivity to Light Post-Treatment
While patients who undergo PDT treatment may be sensitive to some types of light, it’s not a permanent change. Patients may see a temporary sensitivity to light, including natural sunlight and some indoor light, that eventually goes away depending on drug used and dosage.
Generally, light avoidance is required after PDT treatments for varying lengths of time. ALA or methyl ester tend to only cause skin sensitivity on the treatment areas for 24-72 hours. These do not cause sensitivity in other body parts when topically applied.
Recovery after PDT is usually fairly easy. Many patients may experience a mild dryness and faint sunburn in the treated areas. A very small percentage of patients may have moderate or high levels of discomfort and a harder recovery due to extreme skin dryness, redness or burning.
Some patients, typically those with a higher dosage of the photosensitizing agents, experience inadvertent sun exposure post-treatment which causes their reaction to be more severe. Patients should plan to stay indoors and avoid sunlight for the next 24-72 hours, as directed by their physician; avoiding direct sunlight for the first few days is crucial to avoid a worse reaction. Most patients will be able to resume their normal outdoor activities no more than 72 hours after treatment.
Return of Actinic Keratosis Post-PDT
PDT is a very effective treatment; however, that does not mean the patient will not continue to receive periodic treatments for actinic keratoses depending on their individual skin, severity of prior sun damage and level of sun exposure. AK may recur or a new cancer may develop in the same area previously treated or an area adjacent to the treatment area. Some AK lesions are more aggressive than others and will need additional treatment and closer follow-up.
It is important to note that PDT does not work on invasive skin cancers. Other skin cancers may require a biopsy, surgery, radiation, other treatments or a combination of treatments to fully treat the lesions.
Follow-up appointments are extremely important, especially in the first few years after PDT treatment. Many patients are seen by their dermatologist every four to six months for a checkup. Monthly self exams are a good practice for patients being treated for or recovering from skin cancer. Any change or new growth should be promptly check by a dermatologist.