**1. Introduction**

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eng.

232 Highlights in Skin Cancer

Skin cancer shows the highest incidence worldwide, among all cancer types, and is mainly classified in melanoma and non-melanoma subtypes.

Clinical evaluation through dermatoscopy is a widely performed practice, and it is a nonin‐ vasive technique that uses magnification to allow better visualization of the structures immediately below the skin surface. This examination provides morphological criteria for distinguishing various lesions types.

Histopathology is considered the gold standard for diagnosis of skin cancer and other dermal disorders. These two exams together, as well as the location and extent of the injury will determine the choice of treatment.

Treatments such as surgical excision, cryotherapy, topical application of imiquimod cream and 5-fluorouracil cream, and radiotherapy are commonly chosen based on the depth and exten‐ sion of the lesions. Limitations and side-effects of the conventional therapies motivate the development of other techniques. Photodynamic therapy (PDT) is presented as an alternative treatment for basal cell carcinoma (BCC).

PDT has proven to be effective with an excellent cosmetic outcome in the treatment of superficial BCC (sBCC), and recently published guidelines state that PDT can be an effective and reliable treatment option for the treatment of thin nodular BCC (nBCC), and actinic keratosis (AK) [1]. It is a technically simple noninvasive procedure that offers patients at least equal efficacy and a high level of satisfaction and other cosmetic outcome when compared with cryotherapy and topical treatments [2].

© 2013 Andrade et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The term *field cancerisation* or *field effect* is frequently used to describe extensive UV damage with recurrent, multiple AK, and the presence of a tissue with genetically altered cells is a risk factor for cancer development, representing an indication for topical PDT [3].

**3. Photosensitizers**

for indication of PDT in Dermatology.

**Figure 2.** Molecular structures of the PpIX precursors.

The photosensitizers are by definition any substance capable of making an organism, a cell or a substance photosensitive, with the photo-excitation of several types of molecules through energy transfer processes. Porphyrins, chlorines, phthalocyanines are the three main groups of studied photosensitizers (PSs). Porphyrins are the most frequently used PSs, but its systemic administration shows an important adverse factor in Dermatology. Due to the high accumu‐ lation and slow drug clearance from the skin, porphyrins lead to prolonged photosensitization of the organism after application [13]. The commercially available compounds promote a patient photosensitization that lasts for 4-6 weeks. These PDT patients must avoid sun exposure during this period, otherwise skin burns can be induced. This is the major drawback

Photodynamic Therapy for Non-Melanoma Skin Cancer

http://dx.doi.org/10.5772/55242

235

The development of an ideal PDT sensitizer is still a major challenge since several character‐ istics must be contemplated. Main characteristics are: a) photo-excitation with red-infrared light; b) low dark toxicity; c) high stability; d) rapid clearance from the body; e) high affinity

The main reactions observed with biological molecules are lipid peroxidation (cholesterol), cycloaddition (2 +2)-protein (reaction with tryptophan) and Diels-Alder reactions upon molecules in the genetic code (guanine). Porphyrin derivatives are indeed intersting molecules. Compounds such as porphyrins and chlorins, have the characteristics suitable for use in PDT due to the high molar extinction coefficients, high absorptivities in the region of the "thera‐ peutic window" (600-800 nm) and with high quantum yields of singlet oxygen production.

PDT can also be performed with topical use of 5-aminolevulinic acid (5-ALA) or by its ester methyl-aminolevulinate (MAL), which are both precursors in the biosynthesis of protopor‐ phyrin IX (PpIX), a native photosensitizing compound that accumulates in the cells. Proto‐

These compounds must be stored in the form of hydrochloride (R-NH3Cl), since in its neutral form rapidly suffers degradation. Studies including a few with 5-year follow-up, have shown that ALA and MAL-PDT are comparable to other modalities in the treatment of superficial lesions considering their efficacy and with equivalent or superior cosmetic outcomes [14-15]. ALA and MAL are not photosensitizers, they are precursors of endogenous PpIX (Figure 2).

to abnormal cells (selectivity), and f) high rate of ROS production.

porphyrin IX (PpIX) has absorption peaks at 505, 540, 580 and 630 nm.

Our group has extensive experience in clinical PDT in various areas of medicine as in gyne‐ cology [4], infectious disease [5], and in particular in dermatology [6-7], and in this chapter will be discussed the advantagens and indications of the PDT for non-melanoma skin cancer and others conditions.
