Journal of Surgical Oncology 2007;96:554–559 Sentinel Lymph Node Biopsy for Breast Cancer: How Many Nodes are Enough? SHAHEEN ZAKARIA, MBBS, 1 AMY C. DEGNIM, MD, 1 CELINA G. KLEER, MD, 2 KATHLEEN A. DIEHL, MD, 3 VINCENT M. CIMMINO, MD, 3 ALFRED E. CHANG, MD, 3 LISA A. NEWMAN, MD, 3 AND MICHAEL S. SABEL, MD 3 * 1 Department of Surgery, Mayo Clinic, Rochester, Minnesota 2 Department of Pathology, University of Michigan Comprehensive Cancer Center, Ann Arbor, Michigan 3 Department of Surgery, University of Michigan Comprehensive Cancer Center, Ann Arbor, Michigan Introduction: Sentinel lymph node (SLN) biopsy using blue dye and radioisotope often results in the removal of multiple SLNs. We sought to determine whether there is a point where the surgeon can terminate the procedure without sacrificing accuracy. Methods: One thousand one hundred ninety-seven patients from University of Michigan and the Mayo Clinic undergoing SLN biopsy formed the study population. Surgeons removed all SLNs until counts within the axilla were less than 10% of the highest node ex vivo and recorded the order in which they were removed. Results: The mean number of SLNs removed per patient was 2.5 (range 1–9). Approximately 42% of patients had three or more lymph nodes removed, while 19% had four or more lymph nodes removed. Eighteen percent of patients (132/725) at University of Michigan and 22% (103/472) at Mayo Clinic had a positive SLN. Ninety-eight percent (231/235) of patients with lymph node metastases were identified by the 3rd SLN while 100% were identified by the 4th SLN. Conclusion: Among patients undergoing SLN biopsy for breast cancer, the only positive SLN is rarely identified in the 4th or higher node. Terminating the procedure at the 4th node may lower the cost of the procedure and reduce morbidity. J. Surg. Oncol. 2007;96:554–559. ß 2007 Wiley-Liss, Inc. KEY WORDS: breast cancer; sentinel lymph; node biopsy; lymph nodes INTRODUCTION Sentinel lymph node (SLN) biopsy has become a standard method for staging the axilla in clinically node negative patients with breast cancer [1,2]. The benefit of SLN biopsy in providing accurate staging information while avoiding the morbidity of a complete axillary lymph node dissection has been well-documented [3–5]. The SLN is defined as the first lymph node to receive lymphatic drainage from the tumor and is therefore the most likely lymph node to harbor micrometastases if they exist. The practical definition of the SLN is different, however. With the combined use of technetium 99 m-sulfur colloid ( 99m Tc) and blue dye to identify SLN, multiple lymph nodes are often found containing tracer. Any lymph node that exhibits radioactivity, is blue or has a blue afferent lymphatic channel, or is palpably suspicious is excised and labeled as a SLN [6]. A dual tracer technique with blue dye and radioisotope increases both the success rate and the accuracy of the procedure [7–9], but also increases the number of lymph nodes removed per case [10,11]. The degree of radio- activity necessary to excise and define a lymph node as ‘sentinel’ varies among surgeons [6,12–14]. Several authors have demonstrated that the hottest SLN (the node with the highest counts) is not always the node to harbor metastasis [10,15–17], and so a threshold for excising additional SLNs is necessary. What that thresh- old should be, however, remains in question. With a lower threshold, the surgeon is less likely to miss a positive SLN but more likely to remove more lymph nodes per case. Furthermore, the absolute number of counts in the node varies depending on factors such as the dose and *Correspondence to: Michael S. Sabel, MD, 3304 Cancer Center, 1500 East Medical Center Drive, Ann Arbor, MI 48109-0932; Fax: 734-647-9647. E-mail: msabel@umich.edu Received 4 December 2006; Accepted 27 June 2007 DOI 10.1002/jso.20878 Published online 8 August 2007 in Wiley InterScience (www.interscience.wiley.com). ß 2007 Wiley-Liss, Inc.