ORIGINAL ARTICLE 
Annals of Nuclear Medicine Vol. 13, No. 5, 325-329, 1999 

Mammary lymphoscintigraphy with various radiopharmaceuticals in breast cancer
 
Shigeru IMOTO,* Kohji MURAKAMI,** Hiroshi IKEDA,** Hiroyoshi FUKUKITA*** and Noriyuki MORIYAMA*** 

Division of *Breast Surgery and **Radiology, National Cancer Center Hospital East ***Division of Radiology, National Cancer Center Hospital
 
Sentinel node biopsy (SNB) in breast cancer is a promising surgical technique that avoids unnecessary axillary lymph node dissection. To optimize lymphatic mapping with radiopharmaceuticals, mammary lymphoscintigraphy with 30-50 MBq of technetium-99m-diethylenetriamine pentaacetic acid human serum albumin (99mTc-HSAD), technetium-99m-human serum albumin (99mTc-HSA), or technetium-99m-tin colloid (99mTc-TC) were investigated in 69 cases of primary breast cancer. Dynamic early images were obtained during the first 30 or 40 minutes, and static delayed images were obtained 6 hours after tracer injection. Hot spots as sentinel lymph nodes (SLNs) appeared in 5 1 of 69 cases (74%): in early images in 27 cases and in delayed images in 24 cases. SLNs were visualized more frequently in 23_ of the 26 cases (88%) treated with 99mTC-HSAD and in 21 of the 24 cases (88%) treated with 99mTc-HSA than in only 7 of the 19 cases (37%) treated with 99mTc-TC. In 26 of the 51 cases, SLNs were identified as faint spots in delayed images. There was a significant difference in the first appearance of SLNs on the lymphoscintiscan between 43 cases of dense breast parenchyma and 26 cases of fatty breast parenchyma. These results suggest that 99mTc-HSAD or 99mTc-HSA is acceptable for lymphatic mapping, but in cases which have faint spots in delayed images or fatty breast parenchyma, gamma probe-guided SNB may result in failure or misleading false-negative SLNs.
 
Key words: breast cancer, sentinel lymph node, lymphoscintigraphy, breast parenchyma
 
INTRODUCTION 
THE FIRST lymph nodes draining a particular tumor are referred to as the sentinel lymph nodes (SLNs). The histological characteristics of the SLNs are hypothesized to predict the histological findings in the remaining regional lymph nodes. Lymphatic mapping is the first important step in identifying the SLNs, and the SLN sampling technique is called sentinel node biopsy (SNB). Although SLN detection was first described in penile carcinoma in 1977,1 SNB has been successfully reported in melanoma and breast cancer since the early 1990s.2,3 A 

 Received May 1O, 1999, revision accepted July 5, 1999.
 For reprint contact: Shigeru Imoto, M.D., Division of Breast Surgery. National Cancer Center Hospital East (NCCHE), 6-5-1 , Kashiwanoha, Kashiwa. Chiba 277-8577, JAPAN. 
 E-mail:simoto@east,ncc.go.jp 

worldwide feasibility study on SNB in breast cancer is currently under way. In our hospital, SNB with the vital blue dye indigocarmine has been performed since January 1998, and proved feasible and successful.4 We have also been investigating lymphatic mapping and SNB with technetium-99m-labeled agents. In this report, we analyzed mammary lymphoscintigraphy in breast cancer to evaluate the kinetics of different radiopharmaceuticals available in Japan.
 MATERIALS AND METHODS 
We used three different technetium-99m-labeled agents: technetium-99m-diethylenetriamine pentaacetic acid human serum albumin (99mTc-HSAD), technetium-99m-human serum albumin (99mTc-HSA), and technetium-99m-tin colloid (99mTc-TC) (Nihon Medi-Physics Co., Tokyo). Sixty-nine female patients with stage 0-IIIB breast cancer underwent preoperative lymphoscintigraphy with one of the three radiopharmaceuticals between July 1998 and January 1999. Informed consent was obtained before the procedure. The day before surgery, 30-50 MBq (0.8-1.3 mCi) of these agents in 2.5 ml of saline was injected subcutaneously at two or three sites around the primary tumor or near the scar after excisional biopsy. Preoperative lymphoscintigraphy of the involved breast and axillary region in the anterior and anterior-oblique projections was performed using a large field scintillation camera (5 minutes-acquisition in a 512 x 512 matrix). Dynamic early images were obtained every five minutes during the first 30 or 40 minutes after tracer injection (Fig.l), and then static delayed images were obtained 6 hours after tracer injection. The transit time to the first appearance of SLNs and the number of SLNs were recorded. Visualized hot spots were classified as clear or faint spots in early and delayed images.
 About 24 hours after tracer injection, total mastectomy or breast-conserving surgery was performed after an SNB. The scintigraphic hot spots in vivo were detected with a hand-held gamma-ray detector (Navigator, USSC, USA) or radioactive lymph nodes ex vivo were identified with a portable scintillation survey meter. Usually SLNs had 2- to 8-fold radioactivity, compared to non-SLNs as the background, which was counted at around 0.1 uSv/hour by a scintillation survey meter.
 Mammography was also performed in all cases at the initial diagnosis of breast cancer. According to modified Wolfe's classification 5 mammographic parenchymal patterns were designated by four different classifications: a breast with prominent fat parenchyma as N1 , a breast with fat parenchyma and ducts occupying less than l/4 of the volume as P1, a breast with a prominent ductal pattern occupying 1/4 or more of the volume as P2, and a breast with sheetlike areas of irregularly increased density occupying more than a half of the volume as Dy.
 The pathological diagnosis was based on the examination of paraffin-embedded hematoxylin-eosin stained sections of the primary tumor and all axillary lymph nodes.
 Statistical significance was determined by means of the chi-square test for differences between the visualization of SLNs and three radiopharmaceuticals, and by means of the paired t-test for the difference of the numbers of SLNs in early and delayed images. 

RESULTS 
There were no significant differences between the background clinicopathological factors and the use of three radiopharmaceuticals, except for the extensive use of lymphoscintigraphy with 99mTc-HSA for breast cancer without lymphatic invasion (Table 1 ). The visualization of SLNs demonstrated with these radiopharmaceuticals is summarized in Table 2. During the early period of this study, a hand-held gamma ray detector was not available in Japan, and gamma probe-guided SNB was not performed in 22 cases. Hot spots appeared in 51 of 69 cases (74%): in early images in 27 cases and in delayed images in 24 cases. SLNs were visualized in 23 of the 26 cases (88%) treated with 99mTc-HSAD, in 21 of the 24 cases (88%) treated with 99mTc-HSA, and in only 7 of the 19 cases (37%) treated with 99mTc-TC. There was no significant difference between the first appearance of SLNs in early and delayed images no matter which of these radiopharmaceuticals was used. 99mTc-TC visualized significantly fewer SLNs than the other two tracers (p = 0.009). A similar result was seen with the visualization of lymphatic channels (p = 0.030). In 51 of the 69 cases, 49 cases had level I SLNs as hot spots (96%), 5 cases had level 11 or III SLNs (10%), and the hot spots were parasternal lymph nodes in 6 cases ( 12%) and extraregional lymph nodes in 3 cases (6%). SLNs were clearly identified in 25 of the 51 cases, whereas 26 of them finally had faint spots in delayed images (Table 3). The mean number +- standard deviations of SLNs identified with 99mTc-HSAD, 99mTc-HSA and 99mTc-TC were 1.05 +- 1.27 and 1.91 +- l.O, 1.52 +- 2.11 and 1.71 +- 1.31, and 0.57 +- 0.53 and 1.14 +- 0.38, in early and delayed images, respectively (Fig. 2). There was a positive correlation between the number of SLNs in early and delayed images demonstrated with 99mTc-HSAD and 99mTc-TC (p = 0.0002 and 0.030), but not with 99mTc-HSA. In 4 cases 99mTc-HSA hot spots decreased in number in delayed images. According to Wolfe's mammographic parenchymal classification, there was a significant difference in the first appearance of SLNs on the lymphoscintiscan between 43 cases of dense breast parenchyma (P2 or Dy) and 26 cases of fatty breast parenchyma (NI or P1) (p = 0.009) (Fig. 3). In 28 of the 43 cases (65%) of dense breast parenchyma, the SLNs appeared in early images. 

DISCUSSION 
SNB is performed after lymphatic mapping with vital blue dye, radiopharmaceuticals, or both. The means of identification of SLNs may differ in a number of ways, such as the kind of radiopharmaceutical, the site of tracer injection, the dose of radioactivity used, and the interval between tracer injection and SNB (Table 4).3,6-14 Many investigators prefer a short interval between tracer injection and SNB, because hot spots are clearly detected with a gamma ray detector. On the other hand, mammary lymphoscintigraphy in breast cancer can help surgeons to know the number of SLNs and an unexpected drainage to Level II, III, or internal mammary chain 15 Lymphatic mapping and SNB in breast cancer remains standardized. In Western countries, technetium-99m-sulfur colloid and technetium-99m-colloidal albumin are useful for SNB. The sizes of these particles range between 50 and 200 nm, and 3 and 80 nm, respectively.7,8 Unfortunately, they are not available in Japan. From lymphoscintigrams with 99mTC-HSAD and 99mTc-HSA in the present study, SLNs were identified in most cases, but SLNs in half of the cases appeared as faint spots in delayed images at 6 hours after tracer injection. In addition, some hot spots visualized by 99mTc-HSA injection disappeared in delayed images. The particle size of 99mTC-HSAD or 99mTc-HSA is 10 nm or less. 99mTc-HSA can permeate the lymphatic vessels rapidly, but the radioactivity in SLNs may be gradually reduced in delayed images. Another explanation is that the binding between technetium-99m and HSA in 99mTc-HSA may dissociate quickly than the binding in 99mTc-HSAD. It may be difficult to distinguish SLNs from secondary draining lymph nodes (non-SLNs) with gamma probe-guided SNB with 99*Tc-HSA. Lymphoscintigrams with 99mTc-TC showed clear spots in delayed images, but the rate of identification of SLNs in this series was only 37%, because the median particle (about 500 nm) is too large to migrate through lymphatic vessels easily. Some investigators recommended radiopharmaceuticals with a large particle (200-l000 nm) for mammary lymphoscintigraphy.16 The ideal radiopharmaceutical for optimized lymphatic mapping needs to be of such a size that it can flow through lymphatic vessels and be retained in SLNs. At present, SNB combined with blue dye (indigocarmine) and a radiopharmaceutical is the best way to identify SLNs in Japan.
 Our study is the first to demonstrate a correlation between the transit time to SLNs after tracer injection and breast parenchymal patterns. The numerous lymphatic vessels in dense breast parenchyma allow radiopharmaceuticals to reach SLNs easily.
 In conclusion 99mTC-HSAD or 99mTc-HSA is acceptable for lymphatic mapping in breast cancer, but in cases which have faint spots in delayed images or fatty breast parenchyma, gamma probe-guided SNB may result in failure or misleading false-negative SLNs. Although the use of radlopharmaceuticals is limited in Japan, further study is required to determine the standard procedures for mammary lymphoscintigraphy. 

ACKNOWLEDGMENT 
This work was supported in part by a grant for Scientific Research Expenses for Health and Welfare Programs and the Foundation for the Promotion of Cancer Research, and by 2nd-term Comprehensive l0-year Strategy for Cancer Control. 

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