Axillary lymph node status and the number of involved nodes are the most important prognostic indicators for patients with primary breast cancer (66). Axillary lymphadenectomy traditionally was used to detect and quantify the extent of nodal metastasis (67). Before the introduction of sentinel lymph node dissection in the 1990s, axillary lymph node dissection was performed routinely on all patients with early breast cancer. Although axillary dissection is associated with a very low risk of regional recurrence (1% to 3%), the rate of acute complications is as high as 30% (68). Similarly, the risk of chronic lymphedema ranges from 6% to as high 30% (69). Limiting the dissection to level I nodes or random sampling is associated with unacceptably high false-negative rates and should not be done (70). Only one-third of patients with a clinically negative axilla will have nodal metastasis after histopathologic examination of all harvested lymph nodes (71). This means that two-thirds of patients will be exposed to the morbidity of axillary lymph node dissection without proven benefit when performed routinely in the presence of invasive breast cancer.
In 1991 intraoperative lymphatic mapping and sentinel lymph node dissection were introduced to address these problems (72). The concept behind sentinel lymph node dissection is best described by the definition of a sentinel node. The sentinel node is the lymph node that has the greatest potential to harbor metastasis if axillary disease is present. Examination of the sentinel lymph node dissection can accurately predict the status of the entire nodal basin. Removing only one or two lymph nodes can accurately stage the axilla with minimal morbidity. Numerous investigators have demonstrated that, with proper training, sentinel lymph node dissection identification rates range from 90% to 99%, with false-negative rates of less than 5% found in most large studies (73). In one study of 107 patients with T1 and T2 breast cancer who underwent sentinel lymph node dissection followed by axillary lymph node dissection, the sentinel node was successfully identified in 100 patients (93.5%) (73). There were no false-negative results, and the sentinel node accurately predicted axillary status in all 100 patients.