As breast cancer progresses, it can spread to lymph nodes, bean-shaped glands under the armpit. Lymph nodes are part of the body's lymphatic system, which plays an important part in helping the body ward off infection. Discovering that lymph nodes are malignant helps identify the stage of breast cancer and determine the most appropriate treatment. Cancer that has spread to lymph nodes is likely to spread to other areas, including the bones, liver, lungs and brain.
The first lymph-node testing procedure a woman undergoes is typically a sentinel-node biopsy, which involves removing the first 1 to 3 nodes near the breast to test for cancerous cells. The more-invasive axillary-node dissection, which involves removing a small amount of fat containing a cluster of lymph nodes from the underarm area, is performed if a sentinel-node biopsy indicates a malignancy.
How Breast Lymph-Node Status Is Defined
After a sentinel-node biopsy or axillary-node dissection has been performed, the node is examined under a microscope by a pathologist. Post-testing, the level of lymph-node involvement is given a "pN" status, which indicates the number of positive, or cancerous, nodes found. Additional designations are used, but the basic ones are:
- pNX - Axillary lymph nodes cannot be assessed for malignancy
(for example, they had been removed in an earlier surgery) - pN0 - Axillary and other nearby lymph nodes are not malignant
- pN1 - 1 to 3 axillary lymph nodes are malignant
- pN2 - 4 to 9 axillary lymph nodes are malignant
- pN3 - 10 or more axillary lymph nodes are malignant
The number of malignant nodes found will determine the course of a patient's treatment. In general, when cancer has spread to the lymph nodes, prognosis is poor. The more nodes the cancer has spread to, the poorer the prognosis.