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Reliability of sentinel node status in predicting axillary lymph node involvement in breast cancer

James Kollias, Barry E Chatterton, Vivian E Hall, Melissa A Bochner, Brendon J Coventry and Gelareh Farshid
Med J Aust 1999; 171 (9): 461-465.
Published online: 25 October 1999
Research

Reliability of sentinel node status in predicting axillary lymph node involvement in breast cancer

James Kollias, P Grantley Gill, Barry E Chatterton, Vivian E Hall,
Melissa A Bochner, Brendon J Coventry and Gelareh Farshid

MJA 1999; 171: 461-465
For editorial comment, see Ung & Wetzig

Abstract - Introduction - Methods - Results - Discussion - References - Authors' details
- - More articles on Oncology


Abstract Objectives: To assess the reliability of determining sentinel node status in staging regional lymph nodes in breast cancer.
Design and setting: Prospective validation study in a major public teaching hospital, comparing histological sentinel node status with that of remaining axillary nodes.
Patients: 117 women who underwent sentinel node biopsy and axillary dissection for primary breast cancer between 1995 and 1998.
Main outcome measures: Intraoperative success rate in sentinel node identification; false negative rate; predictive value of negative sentinel node status; overall accuracy of sentinel node status.
Results: The sentinel node was identified at operation in 95 patients (81.2%). Tumour involvement of the sentinel node was demonstrated in 29 of 31 women (93.5%; 95% CI, 79%-99%). Sixty-four of the 66 women in whom the sentinel node was negative for tumour showed no further involvement of remaining axillary nodes (standard haematoxylin-eosin histological assessment), giving a predictive value of negative sentinel node status of 97% (95% CI, 89%-100%). The overall accuracy in 95 women in whom sentinel node status was compared with axillary node status was 97.9%.
Conclusions: Histopathological examination of the sentinel node is an accurate method of assessing axillary lymph node status in primary breast cancer and is likely to be incorporated into future surgical management of women with primary breast cancer.


Introduction Axillary lymph node status is the most important prognostic indicator in early breast cancer, and the detection of nodal metastases is a key factor in recommending adjuvant systemic therapy after surgery.1,2 Surgical removal and histopathological assessment of these nodes remains the only accurate way of determining their involvement with tumour. Axillary dissection also reduces the risk of regional recurrence of breast cancer in the axilla,3 as the risk is inversely related to the number of axillary nodes removed.4

However, axillary lymph node dissection is not without morbidity: seroma formation, wound infection, damage to nerves, and reduced shoulder mobility. Of particular importance is lymphoedema, which occurs in 15% and 30% of women.5-8 As a consequence, other, less invasive methods of assessing axillary node status have been investigated (eg, mammography, ultrasound and colour doppler imaging, magnetic resonance imaging [MRI] and positron emission tomography [PET] scanning), but have yet to achieve the accuracy of surgical staging.

Axillary node sampling -- removal of a small number of Level 1 nodes (those below the lower border of the pectoralis minor muscle) -- is associated with fewer complications, and has been proposed as an alternative to complete axillary dissection for staging of the axilla.9,10 However, its efficacy has been questioned.11

With the advent of population-based mammographic screening programs, there has been a dramatic decrease in tumour size and lymph node involvement in women diagnosed with early breast cancer.12,13 Thus, an increasing proportion of women will undergo axillary dissection only to find that their lymph glands are free of disease. Ideally, there should be a method of providing accurate assessment of axillary lymph node status without the need for axillary dissection.

The sentinel lymph node (the first draining node within a lymph node basin) is the first to receive lymphatic drainage from a tumour site. Selective biopsy of this node allows the detection of metastases in clinically normal nodes with a low false negative rate, and has been used in patients with operable breast cancer by several groups.14-19 Their findings indicate that the status of the sentinel node(s) can accurately predict that of the fully dissected axilla. We report our experience of lymphoscintigraphy, intraoperative sentinel node mapping and sentinel node biopsy in 117 women with primary operable breast cancer. Our aims were:

  • To assess the success rate of lymphoscintigraphy and intraoperative lymph node mapping in identifying the sentinel node; and

  • To assess the accuracy of sentinel node biopsy in staging the axillary nodes.


Methods  

Patients A consecutive series of 117 women treated for primary breast cancer at the Royal Adelaide Hospital Breast Unit between June 1995 and August 1998 entered a prospective evaluation of the technique of sentinel lymph node biopsy in breast cancer. Ethical approval for the study was provided by the Human Ethics Committee of the Royal Adelaide Hospital. All women gave written informed consent to participate in the study.

Eligibility criteria were:

  • Operable primary breast cancer (tumour, < 5 cm in diameter), detected clinically and by imaging, and confirmed by cytology, core biopsy or open biopsy;

  • Clinically impalpable axillary lymph nodes; and

  • The usual surgical indications for axillary dissection (ie, invasive, operable cancer).

Patients were excluded if their condition did not fulfil these criteria; if they were pregnant or currently breastfeeding; if there was a high clinical suspicion or preoperative verification of axillary nodal involvement; or if they had metastatic breast carcinoma or a preoperative diagnosis of ductal carcinoma-in-situ.

The women's ages ranged from 31 to 82 years (median, 60 years). Their clinical characteristics are summarised in Table 1. During the period of study, no eligible women refused entry to the study.

Isotope injection technique
The radiopharmaceutical used was 99mTc-labelled antimony sulfide colloid ("Lymph-Flo", Royal Adelaide Hospital Radiopharmacy). The colloid underwent filtration through a 0.2-µ sterile filter, ensuring more than 80% of the filtered particles were smaller than 20 nm. A 32-mm, 25-gauge needle was used to inject 40 MBq of tracer to four sites surrounding the palpable margin of the breast lesion. If the lesion was not palpable, ultrasound localisation was performed, and the injection was given in a similar manner under ultrasound guidance. In the initial stages of the study, 0.5 mL of tracer was injected in each of 82 patients. For the remaining 35 women, the injected volume was increased to 4 mL in four divided doses. In these latter women, the injection site was lightly massaged, and they were instructed to move their arms to encourage lymphatic movement. All radioisotope injections were given on the morning of the day of surgery.

Lymphoscintigraphy and lymph node mapping
After injection, serial anterior and appropriate lateral images were obtained with a large-field-of-view gamma camera (GE XRT, General Electric) at about 15-minute intervals until the initial draining node (or nodes) was visualised (Figure 1). The surface projection of the sentinel node was then marked on the skin with a radioactive marker. Orthogonal projections were made by the established technique of "triangulation"; the marks were joined by a straight line to indicate the base of a right-angled triangle with the node at the apex. Body outline was marked with a radioactive marker, or a transmission image was performed by holding a "flood" source behind the patient.

The intraoperative probe (RMD CTC 4 with audible guidance system, Gammasonics, Melbourne) was calibrated in the Nuclear Medicine Department to the counts detected at the skin surface.

Surgical technique
After completion of lymphoscintigraphy and sentinel node mapping, the patient and hand-held gamma probe were transferred to the operating theatre. In 66 patients, 1-2 mL of 2.5% Patent Blue V dye (Guerbet Laboratories, France; distributed by Fauldings Australia, Adelaide) was injected into the breast parenchyma or subdermal fat overlying the tumour to facilitate intraoperative identification of the sentinel node. Blue dye alone was used in 19 patients before a gamma probe was available.

At operation, a 2-cm transverse axillary incision was made in accordance with the planned axillary lymph node dissection, but taking into account the preoperative skin markings indicating the location of the sentinel node at lymphoscintigraphy. An attempt was made to identify the node in vivo before commencement of axillary dissection. The node was identified by its blue colour (if dye was used) and/or by the hand-held gamma probe (in a sterile sheath). The probe enabled detection of individual nodes with radioactivity levels significantly greater than those of the axillary fat (Figure 2). Sometimes more than one sentinel node was identified. If both dye and radioisotope were used for lymphatic mapping, the blue node corresponded to the most radioactive node.

Once the sentinel node was removed, its activity was reassessed ex vivo and it was sent for histological examination separately from the main axillary nodal specimen. The axillary fat was then examined with the gamma probe in vivo to exclude any residual activity suggesting further sentinel nodes. The axillary skin incision was then lengthened and a level I and II axillary lymph node dissection was performed. The resected axillary tissue was examined ex vivo using the probe to identify any further radioactive or blue lymph nodes not identified during in-vivo examination.

Histopathological examination
All specimens were examined by duty histopathologists at the Institute of Medical and Veterinary Science. The histological tumour features were classified according to tumour size and grade,20 and presence or absence of vascular invasion.21 Generally, sentinel nodes were submitted in their entirety for histological evaluation. Those larger than 1.5 cm were sliced before paraffin embedding. Each node was placed in an individual cassette. At least one section of each node was stained with haematoxylin-eosin (H&E) and examined with light microscopy. Immunohistochemical analysis (antikeratin antibody CAM 5.2, Becton Dickinson) was performed in H&E-stained sections suspected of having metastatic tumour deposits.

The axillary fat was fixed in formalin and the nodes were later isolated from the fat after clearance in Carnoy's solution. Each node was placed in an individual cassette and larger nodes were sliced before being embedded in paraffin. At least one H&E-stained section of each node was examined.

Statistical analysis
A false negative sentinel node was defined as an excised sentinel lymph node which contained no microscopically detectable tumour, but which was associated with at least one tumour-positive node in the remaining resected axillary tissue. The false negative rate and the predictive value of negative sentinel node status were calculated together with 95% confidence intervals. The kappa (κ) statistic for paired data was used to assess the level of agreement between sentinel node status and axillary node status.22 A score of -1 indicates perfect disagreement and + 1 indicates perfect agreement. The corresponding z and P values were calculated. Univariate analysis was used to assess clinical and histological factors that predicted intraoperative sentinel node localisation. Fisher's exact and χ2 tests were used for other analyses between groups.


Results
Lymphoscintigraphy
The sentinel node was identified on preoperative lymphoscintigraphy in 74 of 117 women (63.2%). One sentinel node was identified in 52 women, two were identified in 20 women, and in two further women three and four sentinel nodes were identified, respectively. The sentinel node was identified outside the lower axilla in nine patients (Table 2). A significant increase in sentinel node identification at lymphoscintigraphy was noted after the injection of larger isotope volumes into the breast (77% v 57%; χ2 = 4.15; P = 0.04), while rates of intraoperative detection of the sentinel node also increased (91% v 76%; χ2 = 3.4; P = 0.06).

Intraoperative sentinel node identification
The sentinel node was identified in 95 patients (81.2%) at operation. In 66 women, one sentinel node was identified, two were identified in 20 women, three in eight women, and in one four sentinel nodes were identified. The sentinel node was identified in 35 of the 51 women in whom radioisotope alone was used (68.6%), compared with 18 of 19 women in whom blue dye alone was used (94.7%) and 42 of 47 women in whom both isotope and blue dye were used (89.4%) (χ2 = 9.6; P = 0.008). Of the clinical and histological factors assessed for predicting intraoperative sentinel node identification, only a positive preoperative lymphoscintigram was significant (χ2 = 28.7; P < 0.001) (Table 3).

Predictive value of sentinel node(s)
In 95 patients in whom the sentinel node was identified, 31 had metastatic tumour involvement of axillary nodes (32.6%). Tumour involvement of the sentinel node was demonstrated in 29 of these 31 women (93.5%; 95% CI, 79%-99%), giving a false negative rate of 6.5%. The sentinel node was the only positive node in 13 of 31 women (41.9%). Of 66 women with a negative sentinel node, 64 had no tumour involvement in the remainder of the axillary nodes (by standard H&E histological assessment), giving a predictive value of negative sentinel node status of 97% (95% CI, 89%-100%). The overall accuracy in 95 patients in whom sentinel node status was compared with axillary node status was 97.9% (κ, 0.95; z = 9.3; P < 0.001) (Table 4). Of the 22 women in whom the sentinel node was not identified at operation, six had nodal metastases on histological examination of the dissected axillary nodes.


Discussion The concept of the sentinel lymph node is based on the premise that the first lymph node to receive lymphatic drainage from a tumour site should be the first site of lymphatic spread; that "skip metastases" do not occur; and that the absence of tumour metastases in the sentinel node implies the absence of lymph node metastases in the entire lymphatic basin. This concept was first described in penile carcinoma in 197723 and was later studied in patients with cutaneous melanoma.24 Previous detailed pathological studies of axillary nodes in women with breast cancer have demonstrated a skip metastasis rate of less than 5%.25,26

Our results confirm that the status of the sentinel lymph node(s) predicts the overall axillary lymph node status with a high degree of accuracy, and can thus be used to limit the morbidity associated with axillary surgery. More importantly, the predictive value of a tumour-free sentinel node was 97%. As such, women identified with a sentinel node free of metastatic tumour can be reassured that further axillary lymph node involvement is highly unlikely. Other studies of sentinel node biopsy in breast cancer (using blue dye and radioactive isotope techniques) have shown sentinel node status to accurately determine axillary lymph node status in more than 95% of women.14-19

We still need to deal with the problem that 3% of patients exhibited tumour-positive axillary nodes when the biopsied sentinel node was negative. The optimal method of pathological assessment of the sentinel node remains unresolved and was not addressed in our study. This issue was discussed at the Adelaide Workshop on Sentinel Node Biopsy in Breast Cancer27 and is the subject of further studies by one of us (G F). Giuliano et al28 have found that immunohistochemical studies of sentinel nodes showed micrometastases in an additional 11% of women whose sentinel node was tumour negative on light microscopy. However, similar assessment of two women with false negative results in our study did not reveal metastases.

The implications of micrometastases detected by sensitive immunohistochemical and polymerase chain reaction (PCR) techniques for multidisciplinary care are unknown. They are currently being investigated in trials in the United States (Merrick Ross, Associate Professor of Surgical Oncology, M D Anderson Hospital, Texas, USA, personal communication). Until the answers to this question are available, a large UK trial (ALMANAC) is assessing sentinel node status by conventional microscopy (R Mansell, Professor of Surgery, Cardiff University, UK, personal communication), as this is the current method on which treatment planning is based. These uncertainties emphasise the need for Australian studies to incorporate detailed protocols for pathology assessment of the sentinel node. The prognostic implications of a false negative sentinel node are uncertain, but should be compared with the considerable physical morbidity associated with axillary dissection in lymph node negative women. There is a definite error rate in routine pathological assessment of axillary dissection specimens which may underestimate metastatic disease by 11%-30%,27,29 while unselective sampling of the axilla fails to remove involved nodes in many women.11 The false negative rate must ultimately be minimised by maximal detection of the sentinel node by scintigraphy, careful operative technique and optimal pathological assessment, which requires an experienced multidisciplinary team.

The concomitant intraoperative use of both blue dye and radionuclide methods for lymphatic mapping was particularly useful for sentinel node biopsy. Preoperative lymphoscintigraphy permits identification of the sentinel node and subsequent planning of the site of skin incision. Several radiolabelled colloids are currently in use around the world, but the recent workshop in Adelaide27 identified antimony colloids as having excellent properties for lymphoscintigraphy. This is the only agent available for this purpose in Australia and is able to visualise sentinel nodes in the internal mammary chain as well as in the axillary node group. The blue dye technique facilitated visualisation of the sentinel node at the time of surgery and was supplemented by the use of an intraoperative gamma probe. In all patients in whom both blue dye and radionuclide were used, the blue node corresponded to the "hot" node previously identified on lymphoscintigraphy and identified intraoperatively with the hand-held gamma probe. Furthermore, the identification of a sentinel node at preoperative lymphoscintigraphy was the only factor significantly associated with the intraoperative identification of the sentinel node. Lymphoscintigraphy also demonstrates the number and location of potential sentinel nodes requiring biopsy. The initial rate of preoperative identification of the sentinel node by lymphoscintigraphy in our series was lower than that in published reports. However, this was overcome by increasing the volume of the isotope injection and presumably increasing tissue oncotic pressure, lymphatic uptake and drainage. The importance of isotope volume in achieving successful scintigraphic identification of the sentinel node has also been suggested by others.30

Sentinel lymph node mapping and biopsy are likely to be incorporated into clinical practice, provided they can be successfully performed in most patients, and it can be shown that women with negative sentinel nodes who undergo no further treatment to the axilla are not adversely compromised in terms of disease-free and overall survival. This will be best established by randomised controlled studies comparing sentinel node biopsy with standard axillary surgical management. In addition, these studies should address the implied assumption of lower short and long term morbidity associated with this procedure, the optimal methods of pathological assessment, and allow analysis and comparison with clinicopathological variables in predicting sentinel node status. Studies are currently being undertaken in Europe, the United Kingdom and the United States and it is hoped that Australian women can soon participate in similar trials in Australia.


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(Received 22 Apr, accepted 9 Sep, 1999)


 

Authors' details Royal Adelaide Hospital and Women's Health Centre, Adelaide, SA.
James Kollias, MB BS, FRACS, Staff Surgeon, Breast-Endocrine and Surgical Oncology Unit.
P Grantley Gill, FRACS, MD, Head, Breast-Endocrine and Surgical Oncology Unit; and Associate Professor, University of Adelaide.
Barry E Chatterton, MB BS, FRACP, Director, Department of Nuclear Medicine.
Vivian E Hall, MB BS, FRACR, Radiologist, Department of Radiology.
Melissa A Bochner, MB BS, FRACS, Senior Registrar, Breast-Endocrine and Surgical Oncology Unit.
Brendon J Coventry, FRACS, PhD, Senior Surgeon, Breast-Endocrine and Surgical Oncology Unit; and Senior Lecturer, University of Adelaide.

Department of Tissue Pathology, Institute of Medical and Veterinary Science, Adelaide, SA.
Gelareh Farshid, MB BS, FRCPA, Senior Lecturer, University of Adelaide.

Reprints will not be available from the authors.
Correspondence: Associate Professor P G Gill, Breast-Endocrine Surgical Oncology Unit, Royal Adelaide Hospital, North Terrace, Adelaide, SA 5000.
cbatesbrownswordATmedicine.adelaide.edu.au






Figure 1
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Figure 2
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Box 1
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Box 2
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3: Clinical and histological features predicting success in sentinel node identification at operation

VariableNo. of womenSentinel node identified (%)χ2
(P)

Age (years)
< 503330 (91%)2.84
> 508465 (77%)(0.09)
Tumour site (quadrant)
Upper/outer86 69 (80%)0.2
Lower/inner31 26 (84%)(0.66)
Tumour detection
Screening56 42 (75%)2.7
Symptomatic61 53 (87%)(0.1)
Previous core biopsy
Yes1210 (83%)0.04
No10585 (79%)(0.84)
Previous open biopsy
Yes11089 (81%)0.1
No76 (86%)(0.75)
Scintiscan result
Positive74 71 (96%)28.7
Negative43 24 (56%)(< 0.001)
Operation
Mastectomy31 24 (77%)1.23
Wide local excision5547 (85%)(0.54)
Localised wide local excision3124 (77%)
Tumour size*
< 2cm79 64 (81%)0.03
≥ 2cm36 29 (81%)(0.95)
Tumour grade*
12721 (78%)2.4
25346 (87%)(0.31)
33526 (74%)
Lymphatic/vascular invasion
Negative101 83 (82%)0.44
Positive16 12 (75%)(0.5)
Lymph node status
Negative80 64 (80%)0.2
Positive37 31 (84%)(0.6)

* Excludes two cases of ductal carcinoma-in-situ, diagnosed after excision.
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Box 4
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Received 22 September 2018, accepted 22 September 2018

  • James Kollias
  • Barry E Chatterton
  • Vivian E Hall
  • Melissa A Bochner
  • Brendon J Coventry
  • Gelareh Farshid


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