Axillary Lymph Nodes. When breast cancer becomes invasive, it can spread to the regional lymph nodes. The nodes most commonly involved with metastases are the axillary (armpit) lymph nodes. Surgical removal of regional lymph nodes in breast cancer patients serves two purposes: diagnosis (or staging) and treatment by removing nodes containing cells that could proliferate. At the present time, for patients with an invasive breast cancer, the number of nodes containing cancer is the single most important prognostic indicator for survival.
Axillary Lymph Node Dissection. For many years, the standard surgical procedure for evaluating these nodes, called an axillary node dissection, has been to remove the lymph nodes lying below the axillary vein and those between the major back muscle that attaches to the arm (latissimus dorsi) and the major chest wall muscles beneath the breast (pectoralis major and minor muscles). Until approximately 1995, this was a standard part of the operation of all women with invasive breast cancer. Full axillary node dissection is still indicated in women with obvious involvement of the axillary nodes (either by palpation of enlarged nodes on clinical exam or by image-guided biopsy of abnormal-appearing nodes). Axillary dissection to remove these lymph nodes can be performed in conjunction with standard modified radical mastectomy, with skin-sparing mastectomy and breast reconstruction, or with breast-conserving surgery when a partial mastectomy or lumpectomy is performed. Surgeons may refer to these axillary dissections as removal of level I and level II axillary lymph nodes. Ten or more lymph nodes are usually found by the pathologist in the excised tissue after this type of surgery. Some complications of axillary node dissection include post-operative fluid collections, nerve injury, lymphedema and shoulder dysfunction. Because many women with early-stage breast cancer have negative axillary nodes at the time of diagnosis, research led to the development of the less invasive sentinel lymph node biopsy.
Sentinel lymph node biopsy. Sentinel lymph node biopsy has emerged as an accurate, less invasive alternative to axillary lymph node dissection. It has rapidly become the standard of care for women with invasive breast cancers who have no clinical or imaging evidence of axillary lymph node involvement. The theory behind the technique is that every breast cancer will connect to a lymphatic channel that will then drain to a dominant or a few dominant axillary nodes first before traveling to the rest of the axillary nodes. By identifying the dominant, or “sentinel,” nodes, the axillary nodes as a whole can be accurately determined to be positive or negative. If the sentinel lymph nodes are negative, then the remaining axillary nodes are also reliably negative and do not need to be removed. Although there is still a small risk for nerve injury, shoulder dysfunction and lymphedema, the risk is markedly reduced to less than 5% (versus 20-30% for axillary node dissection), and is of great benefit to the patient. The method of identifying the sentinel lymph nodes is by injecting a blue dye and/or a radioactive particle into the breast at the time of surgery, which is then taken up by the lymphatic system. These tracers track to the sentinel nodes and allow the surgeon to locate them by turning them blue and/or radioactive. The sentinel lymph node biopsy has been shown to be very accurate, resulting in its rapid acceptance by breast cancer specialists.