INTRODUCTION
Sentinel lymph node biopsy (SLNB) has gained widespread acceptance for axillary node
staging in breast carcinoma. Results from the ALMANAC trial confirmed clear benefits
for SLNB in terms of arm function and quality of life measures1.
An accurate and reliable method of assessing sentinel lymph node (SLN) status at the
time of primary surgery is desirable. It would avoid the need for a second operation
in the significant number of patients who are node-negative at diagnosis.
Imprint cytology is a well-recognised simple technique for preparing a surgical specimen
for pathological assessment. The excised SLN is sent fresh to the pathologist who
processes it immediately. The cut surfaces are pressed onto a glass slide, which is
then fixed and stained.
The aim of this study was to assess the use of imprint cytology as an infra-operative
tool for evaluating sentinel lymph nodes in patients with clinically node-negative
breast cancer.
MATERIALS AND METHODS
Data was collected prospectively in a specialist breast unit in a district general
hospital serving a population of 300,000 and treating approximately 170 new breast
cancers each year. Patients meeting the inclusion criteria stipulated by the ‘New
Start’ programme2 were studied consecutively.
Three consultant breast surgeons underwent training in SLNB (under the auspices of
New Start/ Royal College of Surgeons of England). Each surgeon performed 5 cases proctored
by a surgeon experienced in the technique, followed by a further 25 cases without
supervision. After SLNB, a formal axillary node clearance (ANC) was performed.
SENTINEL NODE IDENTIFICATION
Sentinel nodes were identified using a combination of patent blue dye (Patent Blue
V; Guerbet Laboratories Ltd, Birmingham, UK) and radioactive tracer (99mTechnecium-labelled
human albumin nanocolloid particles; Nanocol; Nycomed Amersham PLC, UK). Depending
on the scheduled time of surgery, 0.2mls of either 15mBq (same day) or 20mBq (following
day) 99mTc nanocolloid was injected intra-dermally into the peri-areolar area of the
breast. Uptake of radiocolloid was mapped and a skin mark placed at the level of the
sentinel node, as identified by the static detector.
Following induction of general anaesthesia, 2mls of patent blue dye mixed with 2mls
0.9% saline was injected subdermally and gently massaged for 5 minutes. A small incision
was made in the axilla at the point of maximum radioactivity as determined by the
portable gamma probe (Europrobe, Bright Technologies Ltd, Sheffield, UK). Sentinel
nodes were identified by tracing the blue dye (through direct visualisation of the
blue-stained lymph channels) and the radio-isotope (using the gamma probe). All blue-stained
nodes and/or radioactive foci were excised and sent to the pathology laboratory for
immediate processing and analysis. The gamma probe was used to ensure that radioactivity
levels had fallen to a point that would be consistent with removal of all sentinel
nodes. The axilla was then examined to identify if there were any palpable nodes before
it was cleared in the usual manner.
STAINING AND EXAMINATION OF NODES
Each sentinel lymph node was sectioned transversely into 2mm slices. Depending on
the size of the node, 2–4 imprints were made from each slice by gently touching the
cut surface of the node onto a glass slide. These were air-dried and stained with
Rapi-Diff II stain (Triangle Biomedical Sciences Ltd, Lancashire, UK) before being
reviewed by 2 or more pathologists using a multi-headed microscope. Analysis was performed
during each operation with nodal status consistently determined within 45 minutes
of the specimen leaving theatre. However, as these cases were carried out as part
of the audit phase of SLNB training, results were not relayed intra-operatively and
thus had no impact on the surgery performed.
In some cases, suspicious groups of cells were present on the imprints. However, a
positive report was only given if the number and/or the morphological features of
the cells were sufficient to give a diagnosis of definite metastasis. (Figure 1) All
slices of the sentinel lymph node were formalin-fixed and embedded in paraffin. They
were then examined after Haematoxylin and Eosin (H&E) staining. If negative on H&E,
nodes underwent immunohistochemical staining with the monoclonal anticytokeratin antibody
Clone MNF 116 (Dako, Glostrup, Denmark) using the avidin-biotin-peroxidase complex
method. The pathologist who prepared and reported the imprint was also responsible
for reporting the sentinel lymph node H&E / immunohistochemistry sections, the axillary
nodes and the breast specimen.
Fig 1
positive imprint cytology; Rapi-Diff II stain; x40 magnification
RESULTS
Over an 11 month period, 102 consecutive patients with clinically node-negative disease
had SLNB followed by axillary clearance. The mean age was 58.8 (28-89). The median
tumour size was 20mm. Most patients (60%) had grade 2 tumours, 20% had grade 3 and
the remainder had grade 1. Lymphovascular invasion was present in 33% of patients.
(Table 1)
Table 1
Primary Tumour Characteristics
Mean Age (years)
58.8
Mean Tumour Size (mm)
20
Lymphovascular Invasion (% patients)
33
Histopathology (% patients)
Ductal
63
Lobular
15
Other
22
Tumour Grade (% patients)
1
20
2
60
3
20
An average of 2.3 nodes (1-9) were identified per patient. The identification rate
was 100%. Sentinel node metastases were detected in 41 patients. Metastatic deposits
>2mm were designated macrometastases (Figure 2) while those ranging between 0.2 and
2mm were considered micrometastases (Figure 3). Histopathological analysis of the
axillary clearance nodes revealed metastatic disease in 44 patients, giving SLN biopsy
a sensitivity of 93.2%.
Fig 2
lymph node with macrometastasis; MNF 116 stain; x2.5 magnification
Fig 3
lymph node with micrometastasis; MNF 116 stain; x2.5 magnification
Intra-operative imprint cytology identified 33 of the 41 patients with sentinel node
positive disease. There were no false positives. There were 8 cases where imprint
cytology of the sentinel node was negative but metastases were detected by H&E and
immunohistochemistry. Of these false negatives, 4 were macrometastases and 4 were
micrometastases. Immunohistochemistry did not detect any further metastases on the
H&E negative sections. In total, there were 6 cases of micrometastases. Two of these
were positive on imprint cytology, with one case having micrometastatic deposits in
2 out of the 4 detected sentinel nodes.
These figures give imprint cytology in this study an overall sensitivity of 80%, a
specificity of 100% and a negative predictive value of 88%.
DISCUSSION
It is well accepted that axillary node status is the most important prognostic indicator
in patients with invasive breast cancer. Knowing the nodal status is essential for
correct cancer staging and helps determine the need for adjuvant therapies. However
axillary lymph node dissection (ALND) is associated with significant morbidity, with
up to 60% of women experiencing long-term side-effects. (3). Moreover ALND is unnecessary
for women who have node-negative disease and studies have shown this can be as high
as 70% in those with Tl and T2 tumours.3
Sentinel nodes have been shown to be representative of the presence or absence of
metastases in the remainder of the nodal basin. Sentinel lymph node biopsy is increasingly
being used to predict axillary node status in breast cancer on a world-wide basis.
It allows directed therapeutic node dissections and confines the morbidity of the
procedure to patients who will potentially benefit from removal of involved nodes.4
Data from the randomized controlled ALMANAC trial (Axillary Lymphatic Mapping Against
Nodal Axillary Clearance) confirmed clear benefits for clinically node-negative patients
undergoing SLNB, rather than conventional axillary treatment, in terms of arm function
and quality of life measures.1,5
Various techniques for localization and assessment of the sentinel node have been
employed by different centres over the past decade. Whilst there is no current “optimal”
protocol6, detection using a combination of radiotracer administration, preoperative
nuclear medicine imaging, blue dye injection and intraooperative gamma counting has
been advocated as this appears to increase the sentinel node yield and reduce the
learning curve6,7.
Once harvested, sentinel nodes undergo a thorough histopathological examination. Multisectioning
rather than routine bisectioning is known to decrease the sampling error phenomenon
and increase metastatic tumour detection6. Other studies have shown that cytokeratin
immunohistochemistry staining also increases metastatic tumour detection when compared
with H&E staining6. However immunohistochemical analysis of H&E negative sentinel
nodes did not upstage any of the patients in our study.
The frequently reported methods of intraoperative assessment are frozen section histology
and imprint, or touch-preparation, cytology. Reports of frozen section examination
have described a sensitivity of 44-100% and a specificity close to 100%8. However,
the procedure is time-consuming and the process of freezing, then thawing, the specimen
can introduce artefacts. Furthermore, there is often significant tissue loss, potentially
interfering with subsequent more detailed pathological examination with paraffin sectioning8.
Imprint cytology proved to be a very efficient tool for intraoperative assessment
of the sentinel nodes due to clear lines of communication between theatre and pathology
staff. Although the time varied depending on the size of the node and the number of
nodes requiring analysis, results were usually available within 45 minutes. This is
comparable with the experience of other units carrying out intra-operative imprint
cytology9. Whilst waiting for the result, surgery to the breast can be performed.
The literature suggests that imprint cytology is comparable in accuracy to frozen
sectioning10. In this study the technique had a sensitivity of 80% and a specificity
of 100%. It is important to remember that the definitive SLN status assessed by histopathological
assessment of the node is the standard with which results of intra-operative evaluation
are compared. Hence the detailed sampling carried out may indicate a less favourable
intra-operative accuracy than if a limited sampling of the SLN had been performed.
There were only 8 false negative cases and 4 of these were micrometastases. The sensitivity
of imprint cytology in detecting micrometastases in this study was 33% (Table 2).
This proportion is higher than that found by other centres8 and may be due to the
relatively small numbers in the study. It is noteworthy that most subsequent cases
of micrometastases in our unit have been imprint negative.
Table 2
Sensitivity of imprint cytology
Sentinel node metastases
Final histopathology (no. of cases)
Imprint cytology (no. of cases)
Sensitivity of imprint cytology (%)
Macrometastases
41
33
80%
Micrometastases
6
2
33%
As SLNB becomes more widely used, detection of micrometastasis in sentinel nodes is
increasingly proving a therapeutic dilemma. The prognostic significance and clinical
relevance of these previously occult metastases is controversial11. Hansen et al examined
the John Wayne Cancer Centre experience with 790 patients who had undergone SLNB11.
They observed that, at 8 years, patients with micrometastases in their SLNs had better
prognosis than patients with SLN macrometastases and had prognosis equal to those
with SLN-negative disease.
In contrast, the International (Ludwig) Breast Cancer Study, one of the largest studies
of patients with nodal micrometastases described to date, reported that 83 patients
with micrometastases had a worse disease-free and overall survival after 5 years median
follow-up than did patients who were node-negative on retrospective analysis and serial
sectioning12. A large recently published retrospective review from the Netherlands
also demonstrated that micrometastastes were associated with an absolute reduction
in 5-year disease-free survival of nearly 10%13.
Further data from larger studies with longer follow-up is thus required before definitive
conclusions regarding the relevance and optimal management of micrometastases in sentinel
lymph nodes can be made. Notwithstanding, even if micrometastases were regarded as
positive nodal disease, in clinical practice 80% of patients in this series could
have had their primary tumour and their axilla treated in one operation.
CONCLUSION
Sentinel lymph node biopsy is rapidly becoming the standard of care for patients with
breast cancer. The technique can be learned quickly, but SLNB is a multidisciplinary
process requiring continuous audit.
Imprint cytology has been shown to be reliable for predicting SLN status. This study
has demonstrated that imprint cytology allows a one stage procedure in 80% of patients
with node positive disease, and is to be commended as a useful and practical technique
for those using SLNB for axillary staging in breast cancer.