Sentinel Node Biopsy for Head and Neck Cancer

Abstract

The presence of cervical lymph node metastases remains one of the most important prognostic factors for various solid tumors of the head and neck, including melanoma, squamous cell carcinoma (SCC), and Merkel cell carcinoma (MCC). In patients with clinically evident neck involvement, the regional lymphatics clearly require directed treatment, and this may involve therapeutic neck dissection or radiotherapy. However, the decision whether or not to electively treat patients with clinically uninvolved cervical lymphatics is usually less clear-cut. On the one hand, elective neck dissection simultaneously allows for accurate pathological neck staging and definitive surgical management of patients found to harbor occult metastatic disease. On the other hand, the majority of patients with clinically negative (cN0) necks do not harbor occult disease and would therefore be overtreated by an elective neck dissection. The significant morbidity associated with neck dissection means that this is a real concern, and efforts to minimize the extent of surgical intervention while maintaining oncologic safety are ongoing. The radical en bloc cervical lymph node dissections introduced at the start of the twentieth century have largely been surpassed by more focused surgical procedures, including the modified radical neck dissection (MRND) and more recently, selective neck dissection (SND). The operative morbidity of MRND and SND procedures compares favorably with more extensive dissections, though it remains significant. Sentinel lymph node biopsy (SLNB) represents an extension of this principle; by super-selecting the small subset of lymph nodes most likely to harbor disease, the extent of surgical intervention can be further minimized without adversely affecting diagnostic accuracy. The sentinel node concept states that tumor spread occurs in a stepwise progression from the primary tumor to the first-echelon lymph nodes, before progression to the remainder of the lymphatic basin. These first-echelon lymph nodes, known as the sentinel nodes, can be harvested, examined for the presence of tumor, and used to predict the disease status of the entire basin. In the head and neck region, considerable variability exists in the patterns of lymphatic drainage from each primary tumor site, and the exact location of the sentinel nodes therefore varies between patients. In order to accurately locate the SLNs, a number of techniques may be employed. Preoperatively, radio-labeled tracer is injected in a peritumoral fashion, traveling via the lymphatics to the first-echelon nodes, where it may be detected by gamma camera during lymphoscintigraphy (LSG). A handheld gamma probe is utilized intraoperatively to afford more precise radiolocalization, and some surgeons choose also to inject peritumoral blue dye, easing visual identification of the lymphatics. These comprise the sentinel lymph node biopsy technique, which has been applied to a variety of solid tumors, including breast cancer, malignant melanoma (MM), and penile cancer. This chapter describes SLNB as it relates to the management of solid tumors in the head and neck region, particularly malignant melanoma, SCC, and MCC. A brief history of the development of the technique and its reported accuracy are presented, and the advantages and disadvantages of this relatively new application are discussed. Finally, this chapter explores the possible roles that SLNB may play in the future management of head and neck cancer.