Vessels in the tumor micro environment
The architecture and distribution of vascular structures, determined in part by neoangiogenic factors, angiogenic inhibitors, and tumor–stromal interactions, differ with tumor type. Oncogene activation in tumors drives angiogenesis by the expression of angiogenic factors, such as vascular endothelial growth factor (VEGF) and by inhibiting antiangiogenic factors, such as thrombospondin-1. Fibroblasts and endothelial cells are among the many stromal cells involved in the metastatic process, especially those adjacent to the tumor, that is, on the “tumor front.” The tumor microenvironment refers to tumor cells themselves and the surrounding stromal cells and components, such as cytokines, chemokines, collagen, elastin, and growth factors. The interaction of all microenvironment components play an important role in tumor growth and progression. For example, melanoma cells interact with the stroma by way of cytokines, growth factors, and direct cell–cell contact. Melanoma cells release autocrine growth factors, which stimulate proliferation of melanoma cells, as well as paracrine growth factors, including VEGF and platelet-derived growth factor (PDGF), which are involved in angiogenesis and invasion. VEGF has been detected in vertical growth phase melanoma and melanoma metastases, in contrast to benign melanocytic lesions that show no immunoreactivity for VEGF.
Appropriate dermoscopic technique for the visualization of vascular structures: Care must be exercised to insure that blood vessels, if present, are adequately visualized using dermoscopy. Cutaneous blood vessels can readily be blanched by even slight pressure on the skin surface. Thus, non- polarized dermoscopy utilizing alcohol as the fluid interface, where the glass plate of the dermoscope is pressed firmly against the skin surface, has the tendency to blanch out much of the cutaneous vasculature. To prevent this blanching effect, it is advised that the fluid interface (oil or alcohol) be replaced with ultrasound gel. The high viscosity of gel allows one to place the dermoscope onto the lesion with minimal pressure while maintaining full contact between the glass plate and the skin. Fortunately, polarized noncontact dermoscopes have eliminated the need for direct contact between the glass plate and skin, thereby eliminating the need for a liquid interface. Utilizing noncontact polarized dermoscopy has given us the ability to not only observe blood vessels, but also to indirectly assess the vascular volume within skin lesions. An increased vascular volume can be appreciated as a vascular blush (milky red area, pink veil).