Angiogenic Signaling and Structural Abnormalities in Tumors

Growing tumor needs to be supplied with oxygen and nutrients; hence, the mechanisms responsible for development of new blood vessels are crucial for tumor progression. Enhanced expression of proangiogenic factors enables development of tumor vasculature and subsequent invasion of tumor cells. The key step in these events is decreased oxygen tension within the growing tumor due to limited oxygen diffusion within the tissue. Apart from canonical hypoxic signaling, there are numerous molecular pathways that may modulate angiogenic secretome of cancer cells, such as the action of angiogenic enzymes and microRNAs. Besides tumor cells, also other cellular components of tumor microenvironment play an important role in stimulation of endothelium, out of which the key players are different populations of bone marrow-derived cells of myeloid origin.