From the time malignant tumours have reached a size of two milimetres, they release thousands of malignant cells into the circulation. Most of these cells die or get kiled off. The more aggressive ones survive and remain in the bloodstream as 'Circulating Tumour Cells,' abbreviated as CTCs. These cells have the potential to dispatch into a foreign site in the body in order to proliferate and create a 'secondary cancer,' also known as a 'metastasis.' Their ability to do this is unique to CTCs.
Circulating Tumour Cells were first found in 1869 - yes, that long ago. It is only recently that they have become a topic of much focused attention in research laboratories and Oncology conferences worldwide. Metastatic insufficiency is officially defined as the lack of Circulating Tumour Cells in the bloodstream.
By definition, CTCs are a subpopulation of cancer cells that:
- Have detached from a tumour mass
- Have adopted genetic mutations that enabled migration through the basement membrane (if the tumour is of epithelial origin) and the extracellular matrix
- Have dedifferentiated or undergone the Epithelial-Mesenchymal Transition (carcinoma-derived cells only)
- Have entered into the bloodstream where they circulate as tumour cells with metastatic potential - this is the point at which they are termed 'Circulating Tumour Cells.'
- Have the potential to disseminate and proliferate as a metastatic lesion
- Can stimulate angiogenesis, the growth of new blood vessels
- May have stem-cell like properties
The ability for CTCs to metastasise is made possible by the particular genetic mutations which the CTCs have accumulated and passed onto subsequent generations.
CTCs contain the genes that govern the growth of a secondary cancer. For example, there will be a gene which instructs the making of hormones which will stimulate healthy cells in the new site to make a new network of blood vessels, needed to supply the new tumour with nutrients.
CTCs are now a hot topic in cancer research laboratories worldwide. Due to their capacity to initiate secondary cancers, CTCs are becoming the target for the future of tailoring cancer treatments.
Further reading for general public: Cancer's Circulation Problem - Read article
Further reading for practitioners: Pantel et. al, 2013: Circulating Tumor Cells: Liquid Biopsy - Read article
In this Genostics podcast, Dr. Joachim Fluhrer and Prof. Katherina Pachmann talk about Circulating Tumour Cells: what they are, their importance, and how to detect them. Dr. Joachim Fluhrer: "Circulating Tumour Cell assessment in Australia has been fairly new, it's not yet widely used.