Functional anatomy of lymphatic vessels under the aspect of tumor invasion

In the human body there are about 800 lymph nodes, of which 300 are located in the head and neck area. The lymphatic system begins with initial finger-shaped lymphatic vessels consisting of valveless lymphatic capillaries and precollectors with valves. The precollectors become collectors and transport the lymph to the so-called lymph stems. These vessels lead into the right and left lymphatic duct and into the jugular trunk of the head and neck region. At the end they join into the blood circulation at the junction point of the jugular and subclavian veins. On the basis of the morphology of the initial lymphatics, these are probably the main port of entry of tumor cells. Investigations demonstrate the active invasion into the lymphatic system of melanoma cells. The preference of melanoma cells to adhere to the extracellular fibronectin of the endothelial cells may be a reason for the privileged invasion of the melanoma cells in the lymphatic system, because the extracellular matrix is not protected by a continuous basal lamina like blood vessels. Based on the directed movement of melanoma cells towards the fiber felt, there might be regulative mechanisms influencing the process of targeted adhesion.