**4. Conclusions**

PDT and SDT have great potential to be used as treatments for several diseases, especially cancer. However, when used together (SPDT), their effects can be even more significant. Nonetheless there are many experimental variables that interfere in the outcome of the treatment. This fact leads to difficulties in comparing the results of assays performed by different groups around the world, either *in vitro* or *in vivo*. In order to appraisal the real potential of SPDT, further studies must be carried out in a more standardized manner, controlling the irradiation times, intensities of irradiation by light and ultrasound, type of sensitizer used and even the type and stage of the tumor. Thus, further research in the pre-clinical and clinical areas are crucial. In the case of clinical studies, double blind randomized controlled trials of sonodynamic therapy alone and combined with photodynamic therapy are required.
