April 2009
Cancer Stem Cells may explain some cancer resistance - and may be a future therapy
Looking at yourself in the mirror or flipping through an anatomy text will give you a pretty good idea of the power and diversity of cells. They are the building blocks of all your tissues and organs. Each one of your cells carries your entire genome which holds the complete set of instructions on how to assemble, regulate and modify your body. However, each cell only uses a select and miniscule amount of that information to create the various structures of your body.
Cancer
Cells have the extraordinary ability and versatility to create and maintain your tissues throughout the course of your life. However, this process can be drastically altered by a number of mechanisms that interfere with the normal processing of the genome within the cells that can lead to mutations and novel phenotypes. Once a cell is subjected to such change normal development goes haywire. The disruption in normal cell cycling to uncontrolled growth is known as cancer.
It’s like when your mother tells you to go and clean your room and you don’t listen. Eventually, junk starts piling up everywhere and your room is in utter disarray. Like this, cancer no longer obeys the normal instructions of the information in your genome and cells uncontrollably pile up into masses known as tumours.
Treatment Resistance
Scientists have the seemingly daunting task of coming up with treatments to reduce the tumour growth that arises from out-of-control cellular machinery. The effectiveness of a treatment has been defined by the amount of tumour mass eradicated. However, some cancer cells initially respond but then come back and become resistant to the treatment. This has brought up the question: are treatments targeting the right set of cells?
Cancer Stem Cell (CSC) Theory
A stem cell is a cell type within a tissue that is characterized by two main traits: self renewal and potency. Cancer can be considered to be a disease of the uncontrolled self-renewal of cells. There have been many similarities drawn between stem cells and cancer cells. Evidence indicates that cancer stem cells (CSCs) exist in tumours that drive cancer cell proliferation as well as cancer drug resistance.
The CSC model suggests that only a small population of cells is responsible for giving rise to all the cells found in a particular cancer:
Figure 1. Two different models of tumour cell drug resistance where a) genetic alterations in the cancer cells enable drug resistance or b) resistance is mediated by stem cells which were not targeted by drug treatment.
This means that despite destroying some of the cancer cells, as along as the CSCs are left then the cancer can still extensively proliferate and create new tumours.
The CSC model can explain resistance in cancer treatments and really changes the scope of therapeutic targets in treating cancer. Therapies targeted at shrinking the bulk of tumours may be missing these small populations of cells that give rise to a new or resistant tumour. If indeed only a small population of cancer stem cells is responsible for this trend of ineffective and transient cancer therapies then it may be a good avenue to explore for more effective cancer treatments.
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