Abstract
Colorectal cancer is commonly treated by tumour resection, as chemotherapy and radiation have proven to be less
effective, especially if the tumour has metastasized. Resistance to therapies occurs in almost all patients with colorectal
cancer, especially in those with metastatic tumours. Cancer stem cells have the ability to self-renew, and their slow
rate of cycling enhances resistance to treatment and increases the likelihood of tumour recurrence. Most metastatic
tumours are unable to be surgically removed, thus creating a need for treatment modalities that target cancers directly
and destroy cancer stem cells. Photodynamic therapy involves a photosensitizer that when exposed to a light source of
a particular wavelength becomes excited and produces a form of oxygen that kills cancer cells. Photodynamic therapy
is currently being investigated as a treatment modality for colorectal cancer, and new studies are exploring enhancing
photodynamic therapy efficacy with the aid of drug carriers and immune conjugates. These modifications could prove
effective in targeting cancer stem cells that are thought to be resistant to photodynamic therapy. In order for photodynamic
therapy to be an effective treatment in colorectal cancer, it requires treatment of both primary tumours and the
metastatic secondary disease that is caused by colon cancer stem cells. This review focuses on current photodynamic
therapy treatments available for colorectal cancer and highlights proposed actively targeted photosynthetic drug uptake
mechanisms specifically mediated towards colon cancer stem cells, as well as identify the gaps in research which need
to be investigated in order to develop a combinative targeted photodynamic therapy regime that can effectively control
colorectal cancer primary and metastatic tumour growth by eliminating colon cancer stem cells. Tumor Biology, DOI: 10.1177/1010428317734691