Sentinel lymph nodes are the first lymph nodes reached by cancer cells metastasizing (transferring from one part of the body to another) from a tumor. Breast cancer usually spreads first to the lymph nodes in the axilla (armpit area). These sentinel lymph nodes are the first to receive lymph drainage from the breast and are also the most likely nodes to contain cancer if it has spread.
Surgeons used to perform axillary node dissection (removal of most of the lymph nodes under the arm) to determine whether breast cancer had spread to the lymph nodes. Axillary node dissection may cause numbness and lymphedema (a serious swelling of the arm.)
At Mayo Clinic, however, surgeons routinely perform sentinel lymph node biopsies to determine whether cancer has spread. In sentinel lymph node biopsy, one or two tracers are injected into the breast to identify the sentinel lymph node or nodes. The tracers flow through the lymph channels into the axillary lymph nodes.
A tracer containing a small amount of radioactive material is injected into the breast before surgery. The tracer travels through the lymphatic channels and to the lymph nodes. The surgeon uses a handheld Geiger counter to identify radioactive lymph nodes.
A blue dye may be injected into the breast while the patient is in the operating room. The tracer travels through the lymphatic channels to the lymph nodes. By following the dye released by the tracer, the surgeon can identify the first lymph nodes reached.
Radioactive lymph nodes, blue lymph nodes and any lymph node that feels abnormal will be removed at the time of sentinel node biopsy.
If the sentinel nodes removed are examined and found to be healthy, the chance of finding cancer in any of the remaining nodes is small and no other nodes may need to be removed. Sentinel lymph node biopsy spares many patients the need for a more extensive operation and decreases the risk of complications.
Axillary dissection removes any additional lymph nodes that may contain cancer and allows tests of the remaining lymph nodes to determine if cancer is present.
Axillary dissection is usually performed to remove the remaining lymph nodes in the armpit area if ultrasound-guided fine-needle aspiration biopsy or sentinel node biopsy determines that the lymph nodes under the arm contain cancer. The number of nodes removed averages between 15 and 25.
The lymph nodes removed are examined under a microscope. If the lymph nodes contain cancer, the cancer may have spread to other parts of the body. Mayo specialists may recommend other treatments.