Lymphadenectomy consists of the surgical removal of one or more groups of lymph nodes. It is almost always performed as part of the surgical management of cancer.

This is usually done because many types of cancer have a marked tendency to produce lymph node metastasis early on in their natural history. This is particularly true of melanoma, head and neck cancer, differentiated thyroid cancer, breast cancer, lung cancer, gastric cancer and colorectal cancer. Famed British surgeon Sir Berkeley Moynihan once remarked that "the surgery of cancer is not the surgery of organs; it is the surgery of the lymphatic system".

The better known examples of lymphadenectomy are axillary lymph node dissection for breast cancer; radical neck dissection for head and neck cancer and thyroid cancer; D2 lymphadenectomy for gastric cancer; and total mesorectal excision for rectal cancer.

From http://en.wikipedia.org/wiki/Lymphadenectomy