**8. Conclusion**

From this chapter it can be observed that PDT is most definitely a highly effective and alternative therapeutic treatment for CRC [8]. However, conventional PS drug delivery applications have numerous limitations in relation to solubility and poor tumor subcellular localization specificity [26]. Nevertheless, NP PS drug delivery systems which are surface functionalized with various tumor-targeting moieties can help overcoming some of these limitations be passively, as well as actively enhancing PS drug uptake.

In this chapter, we have shown that there are many positive and promising research studies being conducted *in vitro* and *in vivo*, for the use of PDT in CRC treatment (**Table 1**). We have also evidenced the remarkable potential of passivation NP PS drug carrier platforms (**Table 2**) and specific receptor based PS drug active targeting (**Table 3**), in order to promote the selective absorption of PS drugs in target CRC tumor sites only and so avoid unwanted side effects, as well as overall enhance the PDT treatment of CRC. However, it must be noted that the research studies which have been reported in **Tables 2** and **3** are within early stages of *in vitro* and *in vivo* research and no clinical trials have been performed as of yet. Thus, researchers need to start further exploring specific functionalized NP PS drug delivery platforms for the targeted drug delivery of PSs and effective PDT treatment of CRC within pre-clinical and clinical trials in order to develop optimized standards for this form of CRC therapy [8]. The findings from these studies should drive the application of targeted PDT PS drug delivery to the forefront of oncological interventions as a possible treatment modality for the eradication of CRC.
