How to analyze the diagnostic value of sentinel node biopsy in head and neck cancer

Abstract

In an attempt to more reliably select the lymph nodes that potentially contain metastases, the sentinel lymph node (SLN) concept has been introduced. This has been studied extensively in melanoma and breast cancer, but was recently introduced in the staging of oral squamous cell carcinoma (OSCC). The SLN is likely to be the first lymph node to harbour metastasis and can be used to provide information on the rest of the nodal basin. The SLN is usually identified by peritumoural injection of radioactive colloid and a blue dye. Preoperative lymphoscintigraphy, intraoperative visualization of blue coloration and intraoperative radionuclide detection using a gamma probe allow identification of the SLN. After surgical removal, this SLN is investigated by meticulous histopathological examination using stepped serial sectioning and immunohistochemistry. If the SLN contains metastatic tumour cells, treatment of the neck is recommended, usually in a second procedure [1]. The SLN procedure is considered to be more precise than imaging procedures and less invasive than elective neck dissection. Moreover, it is associated with significantly less postoperative morbidity and better shoulder function as compared with elective neck dissection [2]. Current best practice guidelines for the provision of SLN biopsy (SLNB) in early OSCC patients have been outlined, which provide a framework for the currently evolving recommendations for its use [3]. The sentinel node concept in OSCC has been validated in several studies in which in all patients after SLNB, a neck dissection was performed. The histopathological examination of the neck dissection specimen was used as reference (gold) standard. Although several European studies had validated the sentinel node concept in OSCC, an American multicenter validation study was initiated in which routine histopathological examination of the neck dissection specimen was used as gold standard. This American College of Surgeons Oncology Group (ACOSOG) Z0360 validation study with 140 patients in 25 institutions showed a sensitivity of 90 % and a negative predictive value (NPV) of 96 % [4]. Because routine histopathological examination (and not step-serial sectioning and immunohistochemistry) of the neck dissection specimen was used as the gold standard occult micrometastases might have been missed [5], potentially contributing to higher figures for sensitivity and negative predicting value. After initial studies to validate the SLN concept in early OSCC patients, several small prospective observational studies have been reported. In these studies, a neck dissection was performed only when the SLN contained a metastasis and a watchful waiting strategy was followed when the SLN was tumour-free. Two larger single centre studies found sensitivities and NPVs above 90 % [6, 7]. In an European multicenter study [8] of 134 cT1/2N0 OSCC patients 79 patients underwent SLNB as the sole staging tool, while 55 patients underwent SLNB followed by elective neck dissection (END). For the two groups together, using a reference standard of 5 years follow-up after SLNB staging, a sensitivity of 91 % and a NPV of 95 % were found. The better performance of the SLNB-assisted END group (sensitivity 96 %, NPV 97 %) compared to the SLNB-alone group (sensitivity 87 %, NPV 94 %) can be explained by the use of standard (routine) histopathological examination of the neck dissection specimen versus 5 years follow-up as a gold standard for metastasis [8]. R. de Bree (&) Department of Otolaryngology/Head and Neck Surgery, VU University Medical Center, De Boelelaan 1117, 1081 HV Amsterdam, PO Box 7057, 1007 MB Amsterdam, The Netherlands e-mail: r.bree@vumc.nl