Photodynamic therapy-induced inflammation and adverse effects: An updated review

Photodynamic therapy (PDT) is a non-invasive medical treatment that uses a photosensitizing agent and light to treat various medical conditions and ophthalmology including chronic central serous chorioretinopathy, cancer, skin disorders, and infections. Local inflammation in tumor environment after PDT can be effective in eliciting an immune response to improve treatment efficiency but it causes some early and long-term side effects in local and surround tissues, resulting leads to incidental effects and unwilling consequences such as pain, erythema and infection. Moreover, the mechanism of inflammation in PDT is not clear. Employment of non-optimized protocol including cytotoxic photosensitizer (PS) and fluence and fluence rate during PDT can bring biased outcomes for patients in terms of inflammation and treatment. In PDT, the minimum cytotoxicity and side effects of normal tissue depend on several factors, including the type and location of the tumor to be treated, the PS used, laser power, oxygen level, tumor properties and the patient's individual characteristics. Therefore, careful consideration and adjustment of these parameters are essential for achieving successful PDT outcome. However, in this topical review, various databases, including PubMed, ScienceDirect, and Google Scholar, were used to find relevant studies for this purpose. We highlighted various parameters that influence on cytotoxicity and inflammation response of normal tissue after PDT. Additionally, various pathways that PDT induced inflammation summarized as well as associated side effects have been categorized and finally, we proposed some factors to reduce the side effects and cytotoxicity to the normal tissue in future.