The lymph nodes are part of the lymphatic system and function primarily in filtering out and destroying foreign substances in the blood. While this role of the lymph nodes is invaluable to the body’s fight against infection, it can actually facilitate the spread of cancer. Lymph nodes located near a primary tumor, referred to as regional lymph nodes, are often the depositories of any cancer cells that are able to break away from the original growth.

The cells usually enter the lymphatic system through the lymphatic vessels, which drain and concentrate their materials in the lymph nodes. Cancer cells sometimes begin growing in the lymph nodes, but they may also escape the nodes and then travel to even more distant parts of the body, where they can become lodged and initiate secondary tumor growth. The other principal means of distributing cancer cells of a primary tumor to other organs or areas is via the circulatory system.

When cancer has spread to regional lymph nodes, it is often referred to as nodal involvement or regional disease. If cancer cells become lodged in distant lymph nodes or other remote areas of the body, however, the condition is usually termed metastasis or metastatic disease. Frequently metastasis occurs downstream from the site of the primary tumor, as liberated cancer cells move along the path normally taken by lymph in the lymphatic system or blood in the circulatory system. Yet, many metastatic growths form in locations unexplainable by circulatory means. For example, prostate and breast carcinomas tend to metastasize to bone tissue.

Whether or not cancer cells have spread to regional lymph nodes is generally a key criterion for staging cases of the disease. Stage II and III cancers are generally those in which there is localized advancement and nodal involvement but no evidence of distant tumor growth, though the precise characteristics of these stages vary by cancer type. Since it is usually impossible to know the full extent of nodal involvement without surgery, staging is often not precise, but is rather the best estimation of the advancement of the disease that a doctor can make with available information. In order to err on the side of safety, the regional lymph nodes of cancer patients are often removed during surgery for their primary tumor. The nodes are then examined for signs of cancer, which is a good indication of whether or not metastases are likely to have begun forming in other areas.

By definition, metastatic cancer cannot occur unless a primary tumor has first been initiated. However, in some cases, metastatic cancer may be diagnosed before any other tumor is found. Doctors can be sure that a particular tumor is a metastatic rather than a primary growth based on the cell type, since metastases are comprised of cells from the initial growth. For instance, if abnormal stomach cells are found on an ovary, the tumor must be a secondary one spawned from cells of a gastric tumor. With thorough examinations, a primary tumor can usually be found following the identification of a metastatic tumor.

Lymph Node Metastatic Carcinoma at 20x Magnification - It is widely thought that cancer cells have a special mechanism that enables them to identify and target tissues that are particularly favorable to their growth.

Lymph Node Metastatic Carcinoma at 40x Magnification - With some cancers, surgical removal and inspection of the lymph nodes occurs before tumor removal surgery or any other treatment is given.

Lymph Node Metastatic Carcinoma at 10x Magnification - Occasionally a primary tumor cannot be found in individuals with metastases, in which case the patient is said to have cancer of unknown primary origin.