Abstract
Cancer is a global burden that has prompted extensive research into prevention and treatment, over many decades. Scientific
studies have shown that subset of cells within a tumour, known as cancer stem cells (CSCs), are responsible for tumourigenesis,
metastasis, drug resistance, and recurrences. CSCs have characteristic features of enhanced self-renewal, proliferation, and limited
but multidirectional differentiation capacity. The discovery of CSCs has initiated extensive research into novel cancer treatment
regimes. Evidence indicates that CSCs are resistant to conventional chemo- and radiation therapy leading to treatment failures,
cancermetastasis, secondary cancer formation, and relapse. Because of the observed phenomena in the course of cancer prognosis,
a need for treatment modalities targeting CSCs is important. Photodynamic therapy (PDT) is a clinically approved, minimally
invasive, therapeutic procedure that can exert a selective cytotoxic activity toward cancerous cells while reducing toxicity to normal
cells. It uses a photosensitizer (PS) that becomes excited when subjected to light at a specific wavelength, and the PS forms reactive
oxygen species (ROS) killing malignant cells. Currently, PDT is being investigated as a target specific treatment for CSCs by the
addition of carrier molecules and antibody conjugates bound to the PS. Targeted PDT (TPDT) may be able to not only eradicate
the tumour mass but kill CSCs as well.