**1. Introduction**

Cancer is a group of diseases which cause an abnormal and uncontrolled cell division coupled with malignant behavior such as invasion and metastasis [1]. World Health Organization (WHO) estimates that in 2012, the total number of cancer deaths in the European Union (EU) was 1283101 [2]. For the treatment of cancer various methods have already been discovered and many others are in the process of discovery e.g. chemotherapy (alkylating agents, antimetabolites and natural products - as plant products and micro-organisms), hormonal therapy (with steroids, hormones, anti-estrogens, anti-androgens, gonadotropin releasing hormones analogues, non-steroidal aromatase inhibitors), immunotherapy (interferon, growth factor inhibitors, vaccines, interleukin-2) and different therapies: radiation therapy, photodynamic therapy, surgery, chemotherapy and some traditional therapies [3]. But the anticancer drugs can fail to kill cancer cells for various reasons, the transport of the anticancer drug being governed by physiological and physicochemical properties of the target cell and of the drug itself [4]. These properties include pressure, charge, size, configuration, electro‐ chemical properties, hydrophilicity, *etc*. For the therapeutic agents delivery to the tumor cells, the following problems can be addressed, as follows:


The concept of the nanoparticles which permits higher absorption of the drugs in a specific tissue, and this concept has been applied for hyperthermia, radiation therapy, photodynamic therapy, *etc.* [6]. Meanwhile, the nanoparticles opened new horizons for drug delivery and bringing the term nanomedicines. Nanomedicine is the medical application for diagnosis and

treatment of different human diseases by means of small particles, known as nanoparticles with sizes of 2-100 nm.

The nanoparticles are known by their large surface area, high reactivity, high solubility, reduced side effects and low toxicity [7-9]. The main nanoparticles applied in nanomedicine are: polymeric nanoparticles, liposomes and lipid nanoparticles, micelles, microcapsules, magnetic particles, and carbon nanoparticles (fullerenes, carbon nanotubes, carbon nanofibers, etc) and the nanoassemblies [10-12].

Photodynamic therapy (PDT) as a part of photochemotherapy, is a concerted method where, in addition to light and an administered drug, oxygen is required. PDT represents a concerted action of light, with a sensitizers and an oxygen active specie (singlet oxygen) which prefer‐ entially actions on tumor cells and not on healthy cells. The administered drug is generally a substance which can efficiently photosensitize the formation of singlet oxygen (or other reactive species derived from oxygen), and such species react with different biological targets, and cause cellular damage and finally, the cellular death. Activation of the photosensitizers by light is an essential condition for a successful PDT. Doses of light energy applied in PDT are commonly within 60-200 J/cm2 , though doses may vary from 25 to 500 W/cm2 depending on indications, tissues and light sources [13].

Under such circumstances, this chapter offers the most up–to–date coverage of photodynamic therapy including information on how nanosensitizers, have evolved within the field of cancer therapy and more recently for drugs controlled release in this field, by using personal data correlated with literature reports.
