S

Sentinel lymph node biopsy: biopsy of the first draining node of the regional basin of the tumour. This is usually within the axilla. The sentinel lymph node is usually identified with a combination of a radio-isotope injection the day before (or the morning of the surgery) and a blue dye injected at the time of surgery after the general anaesthetic is given. This is also called the dual localization method. The combination of the radio-isotope and dye is generally considered the most accurate way of accurately identifying the sentinel node. The injection(s) are usually given into the areolar undersurface in the quadrant or segment of the breast that contains the tumour. After the radioisotope is given, a scanning camera is used to identify where the uptake within the nodal basin is. The radioisotope is taken up by one or sometimes two nodes. During the operation, a hand held probe is used to identify the sentinel node. The pre-operative scan, and the count of the hand held probe may help site the axillary incision. At the time of surgery under anaesthetic, a few minutes before the skin incision is made, a blue dye (usually Patent Blue V) is injected in a similar way. This is also taken up by the sentinel node and identified through the axillary incision. The sentinel node is identified by the blue dye within the lymphatic channel and the colour of the node. Each of the blue dye and the radioisotope techniques can be used alone or in combination. Occasionally, the sentinel lymph node is in the internal mammary chain within the chest. This is more commonly associated with medially sited tumours. The sentinel lymph node can be assessed using standard histological techniques. However, as only one lymph node is identified as the sentinel node, the single node may be subjected to more numerous sections and closer histological scrutiny. Special stains and molecular techniques that identify small traces of cancer cells within the node can be performed to identify sub-micrometastasis. The impact of sub-micrometastases in lymph nodes rather than micrometastasis or frankly invasive cancer is not well defined and currently controversial. All knowledge on breast cancer with long term follow-up is based on frankly invasive cancer rather than micrometastasis. The sentinel node biopsy is considerable less interventional or extensive compared with standard axillary dissection. There is a much lower incidence of shoulder stiffness, pain after surgery and lymphoedema after a negative sentinel node biopsy compared with standard axillary dissection. The sentinel node techniques allows selection of patients with early breast cancer for minimally invasive surgery or a conservative approach to the axilla. Patients who are node negative are selected for atherapeutic axillary dissection. In early breast cancer, less than 30-40% of breast cancer is node positive and hence sentinel node biopsy provides an excellent means of offering conservative surgery to the axilla when the axilla is clinically and radiologically apparently unaffected. Clinical and radiological assessment of the axilla is only partly accurate and targeted biopsy of the lymph nodes provides the best way of knowing the actual axillary status. If the sentinel lymph node is positive, most women are advised to have a completion axillary dissection. Axillary radiotherapy is sometimes offered to treat the sentinel node positive axilla but the results of trials to evaluate the role of radiotherapy in this context are awaited. Likewise, the safety of simply observing a negative sentinel node without further axillary treatment is being addressed in clinical trials. Intra-operative assessment of the sentinel node is possible but the result is definitive only when the standard pathology is complete a few days later.

See also under What’s new