The lymphatic system is essential to the body’s response against cancer. It is also one of the body’s most common pathways for the spread of cancer cells to other areas of the body (metastasis).

Lymph nodes produce immune cells and filter foreign material including bacteria and cancer cells from lymph. When the lymph nodes recognize antigens or foreign materials in the lymph fluid, they respond by enlarging and producing additional including lymphocytes to help combat infection. In a person with cancer, immune cells patrol the body searching for cancer cells to destroy. Tumors develop when this immune response breaks down or is overwhelmed.

Also known as swollen glands, enlarged lymph nodes are usually not a serious concern. They are most often seen in people with infections such as sore throats and colds. However, an enlarged lymph node is the most common sign of lymphoma, or cancer of the lymphoid tissue. In this condition, tumors generally develop in the lymph nodes, but may occur in lymphatic tissue located in the stomach, intestines or other organs. Cancer may also develop in other parts of the lymphatic system, including the:

• Bone marrow (multiple myeloma and lymphoblastic leukemia)
• Adenoids
• Tonsils
• Thymus

Enlarged lymph nodes may be a sign that cancer has spread to the lymph nodes from another location. Cancer cells can easily break off from an initial tumor and enter the lymphatic system. Breast cancer, for example, can spread through the lymph vessels to the lymph nodes in the armpit (axillary nodes) and under the sternum (breast plate).

To determine whether a lymph node contains cancerous cells, a biopsy of the area may be ordered. The sentinel lymph nodes are the first lymph nodes to which cancer cells are likely to spread from a primary tumor. As a result, these lymph nodes are often removed and examined under a microscope to determine if the cancer has spread. In order to identify the sentinel lymph nodes, a process known as lymph node mapping may be performed. In this procedure, dyes and radioactive substances are used to identify lymph nodes that contain cancer cells. Once the sentinel lymph nodes have been identified, they may be surgically removed (excisional biopsy) or a sample may be removed for testing (incisional biopsy).

Researchers are studying how new blood vessels are formed promoting the spread of cancer cells to other areas of the body. Researchers are also working to develop ways to enhance the immune system's response to cancer. One method under study is biological therapy or immunotherapy. This method uses substances naturally produced by the immune system to kill cancer cells, slow the growth of the cancer cells or activate the patient’s immune system to more successfully fight the disease.

Biological therapy agents currently being studied include monoclonal antibodies. These are antibodies produced in a lab to resemble those normally produced in the body. However, instead of attacking other antigens as normal antibodies do, monoclonal antibodies are designed to attack antigens on cancer cells. Some monoclonal antibodies have already been approved by the U.S. Food and Drug Administration (FDA) and are currently in use to treat certain types of cancer.

Lymphedema is a condition that can occur when the lymph system is obstructed. When lymph vessels are blocked, it may cause a buildup of lymph fluid in the tissues and result in swelling. It occurs most often in the arms or legs.

There are two types of lymphedema – primary and secondary. Primary lymphedema can occur when lymph nodes or lymph vessels are missing or are not working properly.

Secondary lymphedema is more common. It can develop as a result of cancer or cancer treatments, among other causes. During surgery for cancer, a surgeon may remove some of the lymph nodes located near the tumor for a biopsy. In some cases, lymph vessels may also require removal because they are wrapped around the lymph nodes.

Removing lymph nodes and lymph vessels makes it harder for lymph fluid to flow to other parts of the body. When the remaining lymph vessels fail to remove enough of the excess lymph in the area, the fluid can build up and cause swelling. Scar tissue from lymph node removal or radiation therapy can also cause blockage of the lymphatic system, therefore increasing the risk for lymphedema.

Lymphedema can occur after surgery or radiation therapy for any type of cancer, but is most common in patients with Breast cancer, prostate cancer, pelvic area cancers, lymphoma or melanoma.