For a long period of time, axillary lymph node dissection (ALND) and histopathologic evaluation of the axilla has represented the gold standard for determining the status of the regional lymph nodes, the prognosis, and the appropriate treatment of patients with breast cancer. But in patient with early breast cancer, particularly in the clinical stage I, the axillary nodes fail to contain metastases in over 75% of cases. Sentinel lymph node biopsy (SLNB) with less surgical morbidity and the same accuracy in determining the prognosis and treatment of patients has emerged as a feasible alternative to ALND. SLNB is rapidly becoming the standard of care for a patient with early breast cancer. Axillary lymph node dissection (ALND) is considered unnecessary when sentinel lymph nodes (SLNs) are negative. The main goal of SLNB is avoiding the unnecessary removal of uninvolved lymph nodes and preventing the morbidity of a standard ALND. Recent randomized clinical trials have already proved less surgical morbidity and better QOL for SLNB alone compared with ALND. However, there are several controversies about SLNB remain:
1). What are the indications of SLNB?
2). Should a complete axillary dissection be performed when the SLNB is positive?
3). Can lymphedema occur after SLNB?
4). What is the accuracy of SLNB in patients who have received neoadjuvant therapy prior to surgery?
5). Technical considerations about SLNB

1). The indications of SLNB:
Since 2005, the NCCN guidelines made the recommendation for use of SLNB in single or multicentric T1 and T2 tumors, but not in T3,T4 or inflammatory cancers. Previous axillary and breast surgery, neoadjuvant systemic and obvious palpable axillary nodes are considered relative contraindications. The older age, obesity, and male breast cancer are acceptable, but not recommended in pregnancy women due to lack of safety data. The evaluation of internal mammary nodes(IMNs) by SLNB is acceptable, although the discovery of positive IMNs is considered only beneficial to those who are axillary node negative.
2). Should a complete axillary dissection be performed when the SLNB is positive?
The current paradigm for nodal spread is that metastasis occurs sequentially from the primary tumors to the SLN and then to non-SLNs; thus completion ALND can be avoided in SLN-negative tumors. If the SLN is positive for metastatic disease, the standard management is completion ALND. However, only 50 per cent of patients with metastatic disease in the SLN have further non-SLN involvement. So it has been suggested that completion ALND may be not necessary in women with SLN metastasis but low risk of non-SLN involvement. Isolated tumor cells(ITC), and micrometastasis(0.2~2mm) in SLN may be reasonable for omitting ALND. Recently data from Z0011 trials suggested that even SLN metastasis, those who underwent BCS and SLNB only still have low regional recurrent rate. The data suggested radiotherapy plays some important role in local regional control. Completion ALND may be omitted in case of adjuvant radiation was delivered to the axilla.
3). Can lymphedema occur after SLNB?
Lymphedema represents one of the major factors contributing to postoperative morbidity as it may result in decreased range of motion, pain, weakness, or stiffness of the affected extremity. The incidence of lymphedema after level I and II ALND has been reported in the literature between 5% and 25%. The extent of axillary surgery and postoperative axillary irradiation are the 2 most common factors contributing lymphedema. In Z0011 the surgical complications associated with SLNB plus ALND group was much higher as compared with SLNB only group(75% vs 25%). Rates of lymphedema with SLN were much lower in the same study(13% vs 2%).
4). What is the accuracy of SLNB in patients who have received neoadjuvant chemotherapy(NAC) prior to surgery?
Neoadjuvant chemotherapy is still considered as a contraindications of SLN biopsy. It has been suggested that chemotherapy may interfere with anatomy and physiology of the lympatics and may therefore have adverse effects on the accuracy of SLN procedure. In a meta-analysis of SLN biopsy, the false negative rate of NAC group about 1.5~3 times higher than Non-NAC group. The accuracy of SLNB is controversial in these trials. There were still insufficient data to recommend SLN for patients receiving NAC.
5). Technical considerations about SLNB
Factors affect the identification of the sentinel node are lymphoscintigraphic imaging, Gamma probe, mark on the skin, type of radiocolloid, injection site, obese and elderly, imaging time and doses of tracer. Lymphoscintigraphy is not a substitute for probe-based surgery but is adjunctive. Lymphoscintigraphy is helpful for identifying whether the radiocolloid has drained to the axilla or to other possible sites of drainage. Using larger colloids are preferable. Peritumoral and periareolar injection was preferred. Obsese and elderly patients tend to have a higher frequency of false negative rate. Imaging done soon after injection of radiocolloid is not recommended. Imaging done 6 to 18 hours after injection is considered better. Typically at least 10mBq 99mTc colloid is considered adequate dose.