Photodynamic Therapy (PDT) for Skin CancerMedical editor Johan Tausjø MD
Trond Warloe MD
Oslo University Hospital
Photodynamic therapy was first utilized at Roswell Park in Buffalo, New York with photopherin in the late 1980's. A Canadian group started using used aminolevulinic acid (ALA) in 1990. Oslo University Hospital started development with photopherin and ALA in 1991 and later developed a sensitizing cream based on an ester derivative of ALA which is marketed under the name Metvix®.
Metvix® is a cream containing methylaminolevulinic acid. In cells, this is metabolized to protoporphyrin IX through heme synthesis. Neoplastic tissue breaks down protoporphyrin IX quicker than healthy tissue, which leads to a difference in the concentration of the light-sensitive protoporphyrin IX. When the cells are exposed to the red portion of the light spectrum, a singlet oxygen is created which damages cell mitochondria and cell membranes leading to cell death. This selective effect depends on cream being absorbed into the neoplastic cells, that the difference in the concentration of protoporphyrin IX is great between the healthy and neoplastic cells, and that a sufficient dose of light reaches the tissue.
Both preparation and application of the cream are associated with pain to a varying degree, depending on size, location on the body, and the patient's pain tolerance.
Images of patient before and after treatment:
- Superficial and/or nodular basal cell carcinoma
- Actinic keratoses with squamous cell atypia, possibly in situ or Bowen's disease
- Cure the disease and achieve the best possible cosmetic result.
- Pads of gauze
- Local anesthesia
- Glass microscope slide for cytology
- Lamp with calibrated light dosage for area and time
- Metvix® with occluding bandage
Aspirin use should be stopped 5 days before treatment and warfarin should be stopped 1-2 days before treatment.
Lesions to be treated with PDT must be pretreated by scraping with a knife or curette to remove dead cells and fibrotic tissue as much as possible. Possible bleeding must be stopped before the cream is applied. The creams should be applied over the lesion with an occluding bandage approximately 3 hours before light therapy.
- The lesion(s) are examined by a doctor and suitable lesions are marked and drawn on a bodymap.
- Measure lesion(s)
- In certain cases, a histology or cytology specimen is taken before the treatment is initiated. The cells are scraped from the surface of the tumor with a curette or knife and the material is placed onto a slide.
- For thick tumors, some of the tumor tissue is scraped away before the cream is applied. For thinner lesions, the dead cells are scraped away from the surface.
- In some cases, the skin is punctured with a needle along the periphery of the lesion in order for the cream to be absorbed deeper into the tumor.
- The cream (Metvix®) containing light sensitive material is applied and the lesion is covered.
The patient waits for 3 hours.
- The bandage is removed and the surface cream is wiped away.
- A pad of gauze is applied over the lesion with a hole, which is slightly larger than the lesion.
- The lesion is treated for approximately 8 minutes with a lamp calibrated to deliver a dose of about 37 Joule/cm2, depending on the diameter and depth of the lesion.
- If the lesion is located in the face, the eyes are covered with small shields which are fastened with aluminum tape to exclude light. If the lesion is on the eyelid, a shield is placed underneath the eyelid after local anesthesia is applied to the eye.
This procedure may cause pain. The need for pain medication varies and depends on what area of the body is treated.
- Treatment in the face, fingers, and legs may cause greater pain than treatment on other parts of the body.
- Large lesions are often more painful to treat than smaller ones. For large lesions, local anesthesia is often administered in combination with systemic pain medication. This type of pain is difficult to treat.
- Mild pain can be alleviated by rinsing the lesion with water while irradiating, or by raising the lamp slightly away from the lesion.
One treatment is not always sufficient. For more extensive and deeper lesions, the patient must return for a new treatment after 1-2 weeks.
The pain may, in some cases, last throughout the evening and to the next day.
During the first week, a crust will develop in the treated area. This will fall off during the second or third week where new skin forms underneath. The patient should return to monitor the treatment result after 2-3 months.