Lymphatic mapping and biopsy of the sentinel lymph nodes (SLNs) as a method for pathologically staging breast cancer patients has been extensively evaluated over the past 10 years. The goal of this approach is to stage patients accurately in order to make appropriate decisions about adjuvant treatment, but also to avoid the potential morbidity of conventional axillary lymph node dissection (ALND). A large number of single center and multicenter trials have been reported that indicate the accuracy of several different methods, and the largest prospective randomized trial of SLN biopsy versus ALND, conducted by the National Surgical Adjuvant Breast and Bowel Project (NSABP), completed accrual last year. Other trials with different designs and objectives have also been completed. A great deal of information is now available on the use of this approach to breast cancer staging, but many questions remain controversial, including technical issues and patient selection parameters.

A review of the literature was performed, with particular attention to recently reported results from the NSABP's B-32 trial and the UK ALMANAC trial.

Single center and multicenter validation trials of sentinel node biopsy for breast cancer have demonstrated success rates varying from under 70% to 100%, accuracy rates from 95% to 100%, and false-negative (FN) rates from 0% to 19% [1]. The NSABP B-32 study is a randomized trial comparing SLN biopsy alone versus SLN biopsy plus ALND. Patients with positive SLN by routine histology (without immunohistochemical staining) underwent completion axillary node dissection. A total of 5611 patients were accrued to this trial, and the technical results and accuracy of SLN biopsy were recently reported [2]. At least one SLN was identified in over 97% of the evaluable subjects, and the SLN was positive for metastases in 26%. The FN rate in the group who also had an ALND was 9.7%. The SLN was the only positive node in 61.5% of patients, and only 0.6% of patients had a positive SLN outside of the axilla. SLN identification improved with increasing surgeon experience, and the FN rate was higher after surgical biopsy of the breast versus needle biopsy. In the ALMANAC trial, patients were randomly assigned to SLN biopsy or ALND. Analysis of morbidity demonstrated markedly decreased functional sequelae after SLN biopsy versus ALND, especially in the incidence of sensory loss and arm edema [3].

Issues that are controversial include technical parameters, such as the use of a radionuclide or visible dye alone versus the combination, the sites of injection (subareolar, intradermal, or intraparenchymal), and timing of injection. Several patient selection factors, such as age, obesity, tumor size, and multicentricity, may also impact on the success rate and accuracy of SLN biopsy. Some have advocated routine use of SLN biopsy in patients with ductal carcinoma in situ (DCIS), but it is not clear that this impacts on treatment decisions. It is appropriate to consider SLN biopsy in patients with extensive DCIS diagnosed by needle biopsy, especially if there is a high risk for finding invasive cancer on definitive excision or if the patient is undergoing a total mastectomy. The prognostic significance of 'occult' micrometastases found in SLN by immunohistochemistry is uncertain, but will hopefully be resolved by the NSABP B-32 trial and the American College of Surgeons Oncology Group (ACOSOG) Z0010 study. There is also great interest in being able to predict accurately which patients with a positive SLN have no other nodes involved and could therefore avoid completion ALND. Finally, there is disagreement about the role and timing of SLN biopsy in breast cancer patients receiving neoadjuvant chemotherapy. The FN rates for SLN after chemotherapy have been extremely varied, but in the largest series of patients who underwent SLN biopsy and ALND after chemotherapy (in the NSABP B-27 trial) the FN rate was 10.7% and was not affected by clinical nodal status prior to treatment [4].

SLN biopsy, in experienced hands, is a very accurate method for assessing lymph node status in women with breast cancer and clinically negative nodes. A surprising array of techniques and patients selected for the procedure appear to be successful. SLN biopsy has the potential to reduce drastically the incidence of morbidity related to surgical staging of the regional lymph nodes in women with breast cancer.