Lymph nodes are small glandular structures that filter tissue fluids. They filter out and ultimately try to provide an immune response to particles and proteins which appear foreign to them. There are thousands of these nodes scattered in groups throughout the body. Each cluster is more or less responsible for the drainage of a particular region of the body.

The lymph nodes under the arm (axillary nodes) are the dominant drainage recipients from the breast. When cancerous cells break free from a breast cancer, they may travel through the lymph tubes (vessels) to the lymph nodes. There, the cancerous cells may establish a secondary growth site. The presence of cancerous cells in the lymph nodes proves that cancer cells have traveled away from the primary breast tumor. Therefore, the presence or absence of cancer cells in these regional nodes is an important indicator of the future risk of recurrence. This information is often important in making decisions about whether to use chemotherapy and what type of chemotherapy should be employed.

Unfortunately, removal of the lymph nodes also carries a potential risk of lymphedema, a condition that may cause the arm to swell. Lymphedema can occur early after surgery or many years later. It can be a difficult and disabling condition. Here again, there are trade-offs in risk. When more lymph nodes are removed, more accurate the information about tumor spread is obtained and the chance for tumor recurrence is less. But there is a greater incidence of lymphedema.

There are alternatives to standard lymph-node removal (called axillary node dissection). These alternatives should be considered in each patient's situation. They include

1. replacing standard axillary-node removal with sentinel node biopsy
2. not doing lymph-node removal in patients who will receive chemotherapy anyway based on other information; and
3. not doing lymph-node removal in patients with very small or "favorable" tumors.

Again, these alternatives must be selectively applied with the benefits and risks carefully evaluated.

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