Breast Cancer (2009) 16:219–222 DOI 10.1007/s12282-008-0086-4
ORIGINAL ARTICLE
Identification of sentinel lymph node location based on body surface landmarks in early breast cancer patients Naoko Ueda Æ Keiichiro Tada Æ Satoshi Miyata Æ Mitsuru Koizumi Æ Yoshikazu Kuroda Æ Takuji Iwase
Received: 12 January 2008 / Accepted: 7 October 2008 / Published online: 18 December 2008 Ó The Japanese Breast Cancer Society 2008
Abstract Background It would be extremely useful if the location of the sentinel lymph node in breast cancer could be identified based on body surface landmarks. However, the identification of the sentinel node location by using surface landmarks in many reports is based on empirical methodologies. Methods We studied the distribution of the sentinel node location in 70 breast cancer patients based on the lateral line of the major pectoral muscle, the axillary skin fold that divides the trunk and the upper arm, and the nipple of the breast. Results The location of the sentinel node could be predicted using an ellipse with a semi-major axis of 2.8 cm and a semi-minor axis of 2.2 cm with a probability of 95% for a patient with the mean body size. Conclusion Our data demonstrate that the location of the sentinel nodes can be predicted within a narrow area based on body landmarks.
N. Ueda K. Tada (&) T. Iwase Department of Breast Surgery, Cancer Institute Hospital, 1-37-1 Ariake, Koto-ku, Tokyo, Japan e-mail:
[email protected] S. Miyata The Genome Center, Japanese Foundation for Cancer Research, Tokyo, Japan M. Koizumi Department of Radiology, Cancer Institute Hospital, Tokyo, Japan N. Ueda Y. Kuroda Division of Gastroenterological Surgery, Department of Clinical Molecular Medicine, Graduate School of Medical Sciences, Kobe University, Kobe, Japan
Keywords Sentinel lymph node Early breast cancer Body surface landmark
Introduction The sentinel lymph node is defined as the first lymph node that filters lymph fluid from the site of a breast cancer tumor. When the sentinel lymph node is free from disease, the patient is determined to have node-negative breast cancer with a high degree of accuracy and can safely avoid the morbidity of axillary clearance. Therefore, sentinel node biopsy has become the standard surgical treatment for clinically node-negative breast cancer [1–3]. It would be extremely useful if the location of the sentinel node could be identified based on body surface landmarks. When sentinel lymph node biopsy is performed with the use of only vital blue dye, the site of the skin incision has to be determined according to landmarks. Furthermore, the estimation of the site of the sentinel node based on landmarks is useful for the preoperative evaluation of nodal status. Thorough investigation of the predicted area of the sentinel node with the use of both palpation and ultrasonography can increase the accuracy of nodal status. Several reports have described a predicted sentinel node area on the basis of body landmarks [4–6]. For example, Bass et al. [4] showed that the location of sentinel nodes could be predicted based on the lateral borders of the pectoralis major muscle, the anterior line of the latissimus dorsi muscle, and an axillary hair line. The sentinel nodes were located within a 5-cm circle with a probability of 94%. However, most of these reports have advocated their methodologies without sufficient supporting data. Therefore, we attempted to predict the location of sentinel nodes on the basis of measurements according to
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anatomical landmarks, which is useful for clinical practice with early breast cancer patients.
Patients and methods From April 2003 to September 2004, we performed sentinel node mapping (SNM) in early breast cancer patients. Candidates for SNM had to meet criteria including: predicted size of the invasive breast cancer area that was equal to or less than 2 cm, a node-negative tumor based on palpation and ultrasonography, and no evidence of distant metastasis. A series of 70 consecutive patients was used in the study. The method for sentinel lymph node biopsy using a radioactive agent has been described elsewhere [7, 8]. Briefly, the radioactive tracer used was 1.5 m Ci/ml of 99 m Tc-phytate (Daiichi Radioisotope Laboratories, Ltd.). The radioactive tracer was injected into the subdermal space in the area of the tumor and the retro-tumoral space. The tracer was injected on the day prior to the surgery. In all cases, a lymphoscintigraphy was obtained 1 h after injection. Additionally, vital dye (indigocarmine) was injected intradermally in the peri-tumor space just before surgery. Under general anesthesia, the patient was placed in the supine position with the ipsilateral arm abducted perpendicular to the body line. The point in the axillary region where the maximum gamma count was obtained was denoted as the ‘‘sentinel point’’ (Fig. 1). The center of the ipsilateral nipple was denoted as the ‘‘nipple point’’ (Fig. 1). The intersection point made by the lateral border of the major pectoral muscle and the axillary skin fold that divides the trunk and the upper arm was denoted as the ‘‘pectoral point’’ (Fig. 1). When there were several axillary skin folds dividing the trunk and the upper arm, the lateral one was used for this measurement. The foot of a perpendicular line drawn from the sentinel point to the line passing through the pectoral point and the nipple point was denoted as the ‘‘foot point’’ (Fig. 1). The distances from the pectoral point to the nipple point, the pectoral point to the foot point, and the foot point to the sentinel point were measured in all cases. The distance in centimeters between the pectoral point and the nipple point was denoted as ‘‘L’’ (Fig. 1). The coordinates (x, y) are defined as follows: x = (the length from the pectoral point to the foot point) 9 100/(the length from the pectoral point to the nipple point); y = (the length from the sentinel point to the foot point) 9 100/ (the length from the pectoral point to the nipple point). We assumed that these coordinates (x, y) have a two-dimensional normal distribution. Based on our 70 cases, we can
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Fig. 1 This figure shows the sentinel point, nipple point, pectoral point, and foot point. L is the distance between the pectoral point and the nipple point
estimate the 95% equiprobability ellipse of the coordinates (x, y) by the following formula [9]: ! ! !!0 !! lx l x x x ¼ c2 where R1 ly ly y y 2 1 ec =2 ¼ 1 a ! lx P where and denote the mean vector and the coly varicance matrix of (x, y), respectively. These were P-1 calculated based on the 70 samples. denotes the ! !!0 lx P x denotes the inverse matrix of , and ly y !! ! lx x transpose matrix of : The number ly y ‘‘0.95’’ is substituted for ‘‘a’’ when the 95% equiprobability ellipse is to be drawn. The ellipse corresponding to the equiprobability contour was fitted with the use of the statistical package R 2.3.0 (R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org).
Results The main clinicopathological characteristics are summarized in Table 1. Although all cases were associated with clinically node-negative breast cancer, 15 cases (21.4%) had positive sentinel nodes. Forty-nine patients (70.0%) had dye-stained radioactive sentinel nodes, and 17 patients
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Table 1 Baseline characteristics Mean age (range)
52.1
(24–74)
Mean body height (range)
1.56 m
(1.4–1.68)
Mean body weight (range)
52.5 kg
(40–73)
Mean body mass index (range)
21.6 kg/m2
(14.5–31.2)
0
9
12.9%
I
53
75.7%
IIa
8
11.4%
Stage
Number of removed SLNs (range)
1.9
(1–5)
Number of metastasized SLNs
15
21.4%
Fig. 2 This figure shows the distribution of the coordinates (x, y). The ellipse in this figure shows the 95% (solid line) constant probability contours of the coordinates (x, y)
(24.3%) had radioactive nodes without dye stain. We missed these data in four patients. The mean distance from the pectoral point to the nipple point was 15.9 cm (range 12.5–19.0 cm). The 95% equiprobability ellipse for the coordinates (x, y) is shown in Fig. 2. The center of the ellipse is described by the coordinates (36.33, 19.36). The inflection points of the 95% ellipse are (45.47, 34.03), (47.92, 12.13), (27.19, 4.68), and (24.71, 26.55). The 95% ellipse has a major axis of 17.3 and a minor axis of 13.6. For the distance between the pectoral point and the nipple point of 15.9 cm, which is the mean distance of our series, the semi-major axis is 2.8 cm, and the semi-minor axis is 2.2 cm.
Discussion Our data demonstrate that the location of the sentinel node can be predicted within a narrow area based on body landmarks. The sentinel nodes were located within an ellipse with a semi-major axis of 2.8 cm and a semi-minor axis of 2.2 cm for a patient with the mean body size. The landmarks we used were the nipple, the major pectoral
muscle, and the axillary skin fold that divides the trunk and the upper arm. The radioactive isotope (RI) method is the standard method of identifying sentinel nodes. However, non-RI methods to determine sentinel nodes are still necessary in Japan, because there are many institutes where an RI Laboratory is not available. We believe this issue is a critical one in developing countries. Hence, the establishment of a reliable non-RI method is necessary. One alternative to the RI method is the dye method, which requires no special apparatus and is inexpensive. Furthermore, the sentinel nodes can be identified based on visualization. However, one cannot identify the stained sentinel nodes without making an incision. Therefore, we need a reliable way to predict the location of the sentinel node based on body landmarks for the dye method. Thus, our study contributes substantially to this methodology. The favorable injection site for tracers is unknown for sentinel node biopsy. We use an intra-dermal site in the dye method, which is different from an intra-parenchymal site in the RI method. It is favorable that the markers were injected into an intra-parenchymal site, because an intraparenchymal injection reflects well the mechanism of lymphatic metastasis, compared with an intra-dermal or sub-dermal injection. However, the identification rate in the dye method is inferior to that in the RI method [10]. Furthermore, the identification rate with the use of intraparenchymal sites is inferior to that of intra-dermal injection [11]. Moreover, Borgstein et al. [12] reported that with intra-dermal injection the sentinel nodes are identical to those with intra-parenchymal injection. The mammary gland originates from the ectoderm, and its lymphatic network communicates with the subdermal plexus of the overlying skin [13]. For these reasons, we injected the vital dye intra-dermally. Preoperative evaluation of nodal status is important. Exclusion of node-positive breast cancer patients as candidates for sentinel node biopsy can reduce the chance of false-negative evaluation. For the sake of accurate axillary evaluation, palpation and ultrasonography are recommended [14]. When enlarged lymph nodes are found, we can evaluate nodal metastasis using fine-needle aspiration cytology [15]. These methods require accurate information on the possible location of cancer-positive lymph nodes. Although it is possible for the sentinel nodes to be in the extra-axillary region [16, 17], thorough examination in the predicted axillary area can increase the accuracy of the preoperative nodal status. Based on our results, one practical way to determine the location of the sentinel node is as follows. Identify the pectoral point, where the lateral border of the major pectoral muscle and the axillary skin fold that divides the trunk and the upper arm intersect, and the nipple point, which is
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the center of the nipple. Measure the distance between the pectoral point and the nipple point. This distance, measured in centimeters, is denoted as L. Advance from the pectoral point toward the nipple point for a distance of L 9 0.36 cm. Turn laterally 90°, and advance for a distance of L 9 0.19 cm. This point is the center of the circle with the semi-diameter of L 9 0.17 cm, which is the predicted area where the sentinel node is located with approximately 95% probability. In conclusion, our findings have shown that the location of the sentinel node based on measurements of anatomical landmarks can be predicted within a relatively narrow area. Our data can contribute to the clinical practice of breast cancer treatment.
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9. 10.
11.
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