The lymphatic system moves nonblood fluid around the body, functioning as a network for immune system cells and molecules to travel. The body is capable of forming more lymphatic vessels when necessary, such as when it experiences an injury, and this process is known as lymphangiogenesis. Tumors can hijack the lymphatic transport system and use it to spread cancerous cells. Sometimes, the cancer can also trick the body into lymphangiogenesis. Research is ongoing into the importance of lymphangiogenesis in cancer treatment.
Lymphatic vessels form a network around the body in a similar manner to blood vessels. The major difference between the two networks is that the circulatory system moves nutrients around, and the lymphatic system mostly moves immune system factors around. In the lymph networks are cells such as macrophages, which eat invaders, and lymph nodes, which filter out invaders and allow native cells to pass through. As well as acting as part of the human immune system, lymphatic vessels perform two other major functions.
Blood capillaries transport nutrients to the cells, but some of this fluid does not flow back out from between the cells. The lymphatic vessels recover the leftover fluid and any nutrients still present. This process is necessary for good health as the body needs this fluid for other essential uses. Fat absorption from the lymphatic vessels that line the intestine is another important role of the system.
A natural capability of the body is to create new networks of lymphatic vessels when it needs them. This occurs after tissue injuries and during wound healing if the lymph system has been disrupted. Angiogenesis, which describes the regeneration of blood vessels, can occur along with lymphangiogenesis, which is the creation of new lymphatic vessels. The lymphatic system usually takes longer than the circulatory system to regenerate.
Broken lymphatic vessels can send out new sprouts that grow out and form new vessels. Severed vessels can also reconnect and heal. During the healing process, the affected area of the body usually suffers lymphedema, which is swelling caused by retained fluid.
When cancers spread, they use the existing lymphatic vessels to move around the body. This is called metastasizing and makes cancers harder to treat than if they had been localized to one position. Angiogenesis is a recognized issue with tumors. The extra blood vessels deliver more nutrients and oxygen to the tumor and allow it to grow. Lymphangiogenesis, where a tumor forces the production of more lymphatic vessels, is a less studied area but is being researched for possible avenues into improved cancer treatments.