Angiogenesis

New blood vessel formation (angiogenesis) is an important factor for continued growth and development of both malignant tumours and metastases. Development of new blood vessels in tumours is stimulated by a wide variety of angiogenic factors produced by both tumour cells and stromal cells. In addition, several naturally occurring anti-angiogenic factors have been identified, most notably angiostatin and endostatin. New blood vessel formation in tumours is a complex and dynamic process requiring:

♦ Proliferation of endothelial cells from pre-existing capillaries or venules.

♦ Breakdown of extracellular matrix.

♦ Migration of endothelial cells.

Growth and development of blood vessels within tumours requires the same factors (i.e. increased matrix degradation and altered cell-to-cell and cell-to-matrix adhesion) that are crucial to tumour cell invasion.

New blood vessel formation is important in allowing tumour cells to enter the circulation and a high degree of tumour vascularity increases the likelihood of this. Newly formed blood vessels may be more permeable to tumour cells.

There is extensive interest in angiogenesis as a therapeutic target to prevent both tumour growth and metastases with both naturally occurring and synthetic anti-angiogenic compounds being intensively investigated for possible clinical use.

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