Once they are formed in the bone marrow, lymphocytes circulate in the body and reside in lymphatic tissue including lymph nodes and the spleen, where they search for and await contact with their target proteins. The lymphatic system is a system of vessels (tubes) that is present all throughout the body. Like the more familiar circulatory system, the lymphatic system carries fluid, proteins and cells of the immune system. Red blood cells are not found in the lymphatic system. The two systems (lymphatic and circulatory) are connected. The lymphatic system picks up fluid and cells from around the body and returns them to the circulatory system via ducts located in the neck/shoulder area. The fluid within the vessels is known as lymph.
Like smaller streams merging into rivers that ultimately flow into an ocean, small lymphatic vessels empty their contents into larger ones. The flow leads to collections of grape-like structures knowns as lymph nodes. Many cells in the immune system reside in the lymphatic system for much of their existence.
The lymphatic system is of great importance in cancer for several reasons:
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Cancer cells can spread (metastasize) by getting into the lymphatic system.
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Many cancer types are classified or staged by whether or not cancer cells can be found in lymph nodes close to the site of the original tumor. The logic is this: The lymphatic system is found all over the body so if cancer cells from a tumor have made it that far, they may also have traveled to distant locations.
Learn more about the lymphatic system and metastasis.
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