**5. Future perspectives and challenges**

The greatest challenge when it comes to oncology is prepared drugs with high specificity to promote the death of malignant cells without harming healthy ones. PDT has been used with successful to treat several cases of cancer with a lesser side effects than those treated by conventional chemotherapy. New photosensitizers have been synthesized to increase the photodynamic efficiency on the disease tissues and to facilitate the photosensitizer administration during the treatment. However, the hydrophobicity of new compounds should not limit their use in PDT. The use of nanoparticles as carrier has motivated the research in PDT since results had showed very promising advances in reducing the viability of the cancer cells due to the specificity achieved by the targeted or magnetic drug delivery system and due to the increase of the bioavailability of the nanoparticle. But the synthetic control is a very challenger for preparing a targeted polymeric nanoparticle in order to maintain the reproducibility of the nanoparticulate properties and its efficiency in the cancer treatment. Thus, there is much to be studied about the synthetic particularities of the polymeric nanoparticulate formulation for greater clinical application in the cancer treatment by PDT. In this sense, the development of nanoparticulate systems consistently involves a lot of work to study the several variables and its synergistic or antagonistic combinations that influence the properties of nanoparticulate formulations. Besides, the decrease of the entrapment efficiency of the photosensitizer associated to decrease of the nanoparticle size, the influence of combinatory effect of the photobleaching of encapsulated photosensitizer and the aggregation state of the compound into the nanoparticle, the establishment of adequate loading of photosensitizer into the nanoparticle and the uptake of the polymeric nanoparticle into the disease cells should be considered to development nanoparticulate formulation with high photodynamic efficiency to reduce the viability of the cancer cells.
