5-ALA is used in local PDT of actinic keratoses. Actinic keratosis used to be downplayed as "sun callus" and referred to as a precancerous condition. It is now known that AK should be considered early in situ squamous cell carcinoma (SCC). Although many current treatment options are effective, their cosmetic response is often less than optimal. In contrast, photodynamic therapy is not only effective, but also achieves excellent cosmetic results.
Actinic keratoses (AK) are small rough patches that develop on the skin. The clinical appearance of AK ranges from barely noticeable rough, scaly patches on the skin to raised hyperkeratoses several centimeters in diameter. Most commonly, AK lesions appear as multiple demarcated flat or raised keratotic lesions, but they usually gradually enlarge into broader, raised lesions.1,4
Actinic keratoses are caused by frequent and/or intense UV exposure over many years and mostly occur on skin sites exposed to the sun. Actinic keratoses therefore develop in areas with long-term sun exposure such as the face, ears, hairless scalp, forearms, and backs of hands. The incidence of AK correlates with cumulative UV exposure and therefore increases with each decade of life.1,4 Epidemiologic studies show that the following factors increase an individual's risk for developing AK:1,4
Actinic keratoses are a very common skin disease; millions of people worldwide are affected. Rates have reportedly increased in recent decades.1,4
In the UK, 15% of men and 6% of women have AK, with incidence increasing with age. Up to 34% in men and 18% in women over 70 years of age exhibit actinic keratoses.2 The incidence in the United States ranges from 11% to 26%, but the highest incidence rates are found in countries that are near the equator and have large fair-skinned populations. For example, rates in Australia (Queensland) exceed 55% in men and 37% in women aged 30 to 70 years.3
An AK lesion begins in the epidermis after damage from frequent or intense UV irradiation. This damage causes changes in skin texture and color, resulting in the characteristic blotchiness and raised spots or lesions.1
It is important that actinic keratoses (AK) be treated because the development of an AK lesion is unpredictable. If left untreated, an AK lesion can continue to change in 3 different ways:5
0.1% to 10% of all AK, according to current estimates, will progress to invasive SCC. This transformation is thought to take approximately 2 years.5 Most invasive SCC show evidence of preexisting AK lesions in the process.6 Invasive SCC can cause significant morbidity, through direct extension into the facial structure. In less than 10% of cases, invasive SCC metastasizes with a low survival rate of 5 years.7
Treatment options for actinic keratosis include destructive therapies, topical medications, and field ablation treatments. In general, lesion-targeted treatments are the primary approach for isolated lesions. Field-directed therapies are particularly useful for treating areas with multiple AKs.