Sentinel Lymph Node Biopsy

Introduction

Several cancers, particularly breast cancer and melanoma, are similar in that regional lymph node metastasis greatly affects treatment, prognosis, recurrence rates, adjuvant therapy recommendations, and survival. Therefore accurate assessment and management of regional lymph node disease are of great interest in these patients. Historically, complete lymph node dissection was the standard of care for everyone with invasive breast cancer and melanoma. Although associated with high morbidity, including rates of lymphedema up to 40%, the operation was required to treat regional lymph node disease, to correctly stage the patient, and to allow for appropriate adjuvant radiation and systemic therapy recommendations.

Sentinel lymph node biopsy (SLNB) has dramatically changed the management of breast cancer and melanoma patients. Although first described in 1977, years of research were required to prove the technique accurate and applicable. After the Z11 study in the early 2000s, SLNB was adopted as the standard of care for breast cancer patients with T1-T3 disease who are clinically node negative. During a similar timeframe, the Multicenter Selective Lymphadenectomy Trial (MSLT-1) helped to establish SLNB as the standard of care in clinically node-negative melanoma patients as well.

Selection of Dye/Radiotracer and Injection Sites

For breast cancer, the choice of single-agent (blue dye or radiocolloid alone) versus dual-agent (both blue dye and radiocolloid) mapping has been the subject of multiple studies. Although some studies show equivalence between these techniques, the dual tracer technique has been associated with improved sensitivity and specificity and thus is often preferred. However, there are no current national guidelines regarding dye use for SLNB, so the final choice of blue dye or radiolabeled colloid is dictated by surgeon preference and patient characteristics. Blue dye should never be used in pregnancy. In addition, it is important to remember the potential side effects of methylene blue (skin necrosis) and isosulfan blue (anaphylaxis) when selecting an agent for lymphatic mapping.

For breast cancer, the injection site for the blue dye or the radiotracer can be either peritumoral or periareola ( Fig. 58.1 ). Intradermal injection is contraindicated because of skin discoloration, so most injections are done into the breast parenchyma or subdermal levels. The injection may be performed in nuclear medicine preoperatively but may also be performed intraoperatively by the breast surgeon at the start of the case.

For melanoma, intradermal injection of the dye is recommended and is usually performed around the site of the tumor (or around the biopsy site if the primary tumor was previously removed). Any discoloration of the skin is irrelevant because the skin is removed as part of wide local excision. Most often dual tracer technique is used for melanoma. Whereas breast cancers drain to the axillary lymph nodes preferentially, variable lymphatic drainage is common with melanoma depending on location. Thus the radionucleotide injection for melanoma is often performed preoperatively in nuclear medicine so that lymphoscintigraphy can be used to identify the draining nodal basin. If injected in the operating room, it can be more difficult to identify the appropriate nodal basin using the gamma probe alone.