Sentinel European Node Trial (SENT): 3-year results of sentinel node biopsy in oral cancer

1. Introduction

Head and neck squamous cell carcinoma is the eighth most common cancer worldwide in males and is increasing significantly amongst females [1] Approximately half the patients with oral cancer present with stage I/II disease and up to 33% [2,3] have occult cervical disease undetectable by current imaging techniques (computed tomography [CT]/magnetic resonance imaging [MRI]/ultrasound/positron-emission tomography)[4,5].
Cervical metastasis is associated with a 50% reduction in cure. Consequently, if the estimated chance of metastasis exceeds 20% [6], current practice is to offer an elective neck dissection (END) rather than ‘wait and see’ policy [7]. The corollary of this strategy is that up to 80% of stage I/II patients undergo an unnecessary neck dissection.
Sentinel node biopsy (SNB) is capable of detecting occult metastases in head and neck cancer [8e11] and is becoming established in a range of other cancers [12,13].
SNB offers a potential solution for management of the N0 neck but at the present time it is not widely offered. There is a paucity of data on the expected success of the technique, particularly with respect to the accuracy of sentinel node (SN) detection, disease recurrence and survival. The Sentinel European Node Trial (SENT) study population is the largest cohort of oral cancer patients in which SNB was performed as a sole staging procedure without concurrent END. The end-points of this study were SN identification rate, false-negative rate (FNR) and diseasefree survival (DFS) at 3 years post-recruitment. Because of the lack of contemporaneous SNB data, we have used comparable data from patients treated by conventional END as well as SNB data in similar tumour groups who routinely use SNB in management of the neck to contextualise the results. The aim of this investigation was to assess whether SNB is a safe and reliable therapeutic technique in T1eT2 oral squamous cell carcinoma.

2. Patients and methods

A European multicentre prospective study (October 2005eOctober 2010) was approved by the European Organisation for Research and Treatment of Cancer and local ethics committee, with patients providing informed consent. Eligible patients had 0.5- to 4-cm squamous cell carcinoma with an N0 neck on CT and/or MRI (<1.1 cm or up to 1.5 cm in level II and no atypical
features)  ultrasound-guided fine needle aspiration cytology. SENT was principally designed for oral squamous cell carcinoma; however, tumour-bordering structures of the oropharynx which were transorally accessible and resectable (without mandibular split or robotic techniques) were also included. Tumour location was recorded according to Systematized Nomenclature
of Medicine (SNOMED) topography code [14] apart from ‘oral tongue posterior 1/3’ which related to tumours of the posterior part of the oral tongue and not tongue base tumours.
Patients with a previous malignant neoplasm of the head and neck or any disease that might have altered lymphatic drainage were excluded. Patients had to be fit enough to tolerate a completion neck dissection if the SNB proved positive.

sent-tab1

A total of 480 cases were recruited prospectively from 14 European centres. The criterion for unit participation was completion of at least 10 successful training SNB procedures (validated against neck dissection) prior to recruiting to SENT. Sixty-five patients (14%) were excluded from the final analysis (Table 1).
When adjuvant treatment (radiotherapy [RT] or chemoradiotherapy) was given during the follow-up period for close margins or a metachronous primary tumour (NZ17), patients were excluded on the premise that radiation fields extended into the upper neck and could theoretically extinguish missed metastases, thereby erroneously reducing the SNB FNR. Pre-operative lymphoscintigraphy was performed within 24 hours of surgery after Tc-99m nanocolloid (Nanocoll/Nanocis) was injected using a standardised technique [15] at four points around the tumour (median dose 57 MBqeinterquartile range 60 MBq). The position of the SNs was marked on the neck. At surgery, the SNs were detected by a hand-held gamma probe and in 164 of 415 patients (39%), peritumoural injection of blue dye was given (SN recorded by colour, radiation count and site in neck). Lymph nodes with radiation count more than three times the background
activity were considered SNs. If a radiation hot spot was in more than one neck level (SN versus second or third echelon nodes), then the primary SN was decided by maximum radiation count.
The SNs were fixed in 10% neutral-buffered formalin and a validated protocol for analysis was followed [16]. Five serial sections were cut every 150 mm through the block and one from the centre of each series was stained with haematoxylin and eosin (H&E). If metastasis was still not detected, an adjacent section at each level was stained with anti-pan cytokeratin antibody AE1/3. If cytokeratin was detected but the viability of the cells was in question, the adjacent serial sections were examined stained with H&E. One center (67 in 415: 16% of patients)
cut a single frozen section (FS) from the midline of the node, with remaining specimen examined as above. This allowed on-table diagnosis [17] and immediate neck dissection if the FS was positive.
SENT recorded metastasis as viable or non-viable deposits sized in terms of percentage of the total node. For the purposes of this report, SNBþ nodes were retrieved where possible (75 in 94 cases, 80%) and regraded according to the Union for International Cancer Control (UICC) Seventh Edition guidelines [18]. Deposits were re-classified as isolated tumour cells (ITC,
<200 cells or <0.2 mm deposit with no stromal reaction), micrometastasis (0.2e2 mm), and macrometastasis (>2 mm). In the SENT cohort, ITC was treated as a positive neck (completion neck dissection performed within 3 weeks).
Tumours were excised aiming for pathological clear margin of >4 mm, and all defects were closed without free flap reconstruction. Neck specimens were pinned out maintaining alignment and fixed in neutral-buffered formalin. They were examined macroscopically and byroutine H&E with cervical metastasis mapped by neck level. Demographic data, pathological features, location of SN, and survival data were collected for each patient.

sent-tab2
Statistical analysis was performed using R survival package [19]. Univariate survival analysis models were built using KaplaneMeier product-limit estimator for overall survival (OS), disease specific survival (DSS) and DFS, and multivariate and models with univariate continuous covariates were built using Cox proportional hazards model. Table analysis on 3-year outcomes (such
as recurrence within 3 years of SNB) was performed using either chi-square or Fisher’ exact to test significance, depending upon the distribution of the variable in
question.

3. Results

The patient and carcinoma characteristics are shown in Table 2.
3.1. Lymphatic drainage characteristics A total of 483 neck sides were examined from415 patients with 1342 SNs harvested. There were a mean of 2.75 SN per neck or 3.2 SN per patient (range 1e10), with an average size of 11.8 mm (range 3e30 mm). The primary tumour was positioned in the midline in 11.4% (NZ46) and laterally in 88.6% (NZ369) of cases. Lateral tumours
drained ipsilaterally in 87% of cases (320 in 369) but in 10% (40 cases) they drained bilaterally and in 2.4% (9 cases) exclusively to the contralateral neck. Sixty percent (28 in 46) of midline lesions drained bilaterally.
3.2. Occult cervical disease SNB detected metastasis in 94 patients (23%), 16 of whom had extra-capsular spread (17%). Of the 75 cases classified by the UICC guidelines, 12 (16%) contained
ITC, 36 (48%) contained micrometastasis and 27 (36%) macrometastasis.
Fifteen patients with a negative SNB subsequently developed isolated cervical metastasis with a negative primary tumour site (one with concomitant distant metastasis) and these were recorded as a false-negative biopsy. Therefore, of 415 patients, 109 had occult metastasis. SNB had a sensitivity, negative predictive value and FNR of 86%, 95%, and 14%, respectively. The
FNR, sensitivity and negative predictive value for the three most common tumour sites are shown in Table 3.
In the 49 patients with unexpected bilateral or contralateral drainage from a lateral carcinoma, a positive SN was identified in seven (two bilateral and five solely contralateral).
All 94 patients with a positive SNB underwent neck dissection. In seven cases, dissection was bilateral, giving a total of 101 neck dissections, of which 47% (47 in 101)
were selective, and the remainder modified radical.
In 85%of cases, no further positive nodeswere found in the completion specimen. Of the patients with additional positive non-sentinel nodes, 13 in 15 (87%) were located in
the same neck level as the SN or an adjacent neck level.

sent-tab3
3.3. Outcome
In this cohort of patients, 3-year figures for OS, DFS and DSS were 88%, 92% and 94%, respectively.
Disease recurred in 56 patients (Table 4). Univariate analysis of the factors that affected outcome (overall survival) was investigated with
KaplaneMeier survival analysis for categorical variables and Cox proportional hazards for continuous variables (such as age of patient) (Table 5, Fig. 1e3). A
multivariate Cox proportional hazards model was then run with all variables that showed a univariate p value <0.25. The resulting multivariate Cox proportional hazards model found that the grouped number of positive nodes (pZ0.0008) and SN status (pZ0.003) were the only significant factors.
3.4. Complications
Morbidity of SNB was minimal. Minor complications were seroma [1], haematoma [8], local infection [3], and lymphoedema [1]. There were two notable complications:sent-tab4
one phrenic nerve palsy and one patient had a cerebellar stroke secondary to surgery.
Mean hospital stay following SNB and primary tumour resection was 5.7 d (range 0e30) with 161 patients discharged within 3 d of their surgery. Lengths of stay varied considerably by country (average of 9 d in Belgium compared to 3 d in Denmark).

Adjuvant therapy (RT or chemoradiotherapy) was given to 12% (48 in 415) of patients. In the SNB-positive group, 27% (25 in 94) received adjuvant therapy (more than one positive node or extracapsular spread e ECS) but was used more freely (80%) in the false-negative SNB group (12 in 15) to help salvage patients. There was no significant survival difference between those with and without adjuvant radiotherapy (pZ0.67).

 

 

sent-tab53.5. Adjuvant therapy
Adjuvant therapy (RT or chemoradiotherapy) was given to 12% (48 in 415) of patients. In the SNB-positive group, 27% (25 in 94) received adjuvant therapy (more than one positive node or extracapsular spread e ECS) but was used more freely (80%) in the false-negative SNB group (12 in 15) to help salvage patients. There was no significant survival difference between those with and without adjuvant radiotherapy (pZ0.67).
4. Discussion
The results of the study demonstrate clearly the value and safety of SNB for staging the N0 neck in routine clinical practice. The principal aim of the study was to establish whether SNB is a safe oncological procedure. This has been confirmed with DFS of 92% at 3 years following treatment. The second objective was to determine, in the context of oral and oropharyngeal cancer, whether SNB was an effective diagnostic test for microscopic deposits of metastatic cancer. The study showed conclusively that the SNB technique works effectively in the oral cavity.
The injection of radiotracer (lymphoscintigraphy) will define an SN in the vast majority of patients (>99%).
In this cohort of patients with a 3:1 distribution of T1:T2 oral squamous carcinoma and radiologically N0 neck, it transpired that 26% (109 in 415) had occult cervical disease. The SNB technique failed to detect occult metastasis in 14% (15 in 109) of patients, only half of whom (53.3%: 8 in 15) were amenable to salvage.
This is somewhat counterbalanced through identification of unexpected contralateral lymphatic drainage by SNB. This occurred in 12% (49 in 369) of cases and in seven instances, the contralateral SN was positive. Thus, 6% (7 in 109) of occult cervical metastasis would have been missed by conventional treatment of ipsilateral neck dissection.
In head and neck cancer, historically, there has been concern that biopsy of suspected neck metastasis would facilitate dissemination of tumour in the neck.

sentfig1 sentfig2 sentfig3
A systematic review [20] of 109 papers calculated regional recurrence rates of 13% in surgically treated early-stage oral cancer. A further review of 164 [21]
patients with pT1eT2 tongue SCC staged pN0 after END reported a regional recurrence rate of 18%. The results of SENT when reported in an identical way show the neck recurrence rate for SNB andSNBþ and the total group were 5%, 15% and 7.5%. The low rate of regional recurrence argues against SNB causing tumour spillage and in turn neck recurrence.
Two- and 5-year overall survival in early oral and oropharyngeal carcinoma is in the region of 82% and 76%, respectively [20,22]. In this study, overall crude (88%) and DSS (94%) are unlikely to change significantly and suggest strongly that SNB does not adversely affect outcome. An FNR of 14% is similar to that reported in a meta-analysis of 25,000 melanoma patients (12.5%) [23] and 20% FNR in 10-year followup of the Multicenter Selective Lymphadenectomy Trial (MSLT) trial in melanoma [24]. However, this is on the borderline of acceptability and we should aim
to reduce this to the 7% FNR accepted in breast cancer [25]. Further analysis of the factors associated with a false-negative biopsy is warranted but initial review of our data suggests that operator factors are principally responsible for the FNR. It is well established that there is a learning curve to the SN technique [11].
It is of particular note that previous studies [9,11] indicated that SNB was less reliable for tumours in the floor of mouth presumably due to the close proximity of the injection site to the primary draining nodes. The same association was not found in this study. The major positive patient benefit of SNB is that in this series 71% of patients were spared neck dissection
with consequent improved function and reduced morbidity [26,27]. There were also 47 patients with midline tumours who by convention would have received bilateral neck dissection. In this group, only eight underwent bilateral and eight unilateral dissection based on positive SN. A low complication rate as well as

a reduced in-patient stay supports the economic argument for SNB over END [28]. The identification of aberrant drainage patterns is a huge advantage of SNB and will also have application in
patients with second primary tumours where a neck dissection has already been performed and drainage has been disturbed. The disadvantage of blanket ipsilateral END is illustrated in the study of pN0 necks treated by END [21]. In this series, the regional recurrence rate of 18% seems high but it is worth noting that in over onethird of patients (39%) recurrence occurred in the
contralateral neck. One further advantage of SNB is that because the tissues have not been significantly disturbed, comprehensive salvage surgery is possible if a recurrence
is detected promptly. Our results have also shown that the metastasis type (ITC, micrometasis, macrometastasis) was a prognostic value for overall survival. This confirms
recent findings [29,30] and may be important for stratifying personalised treatment in the future. At the present time, SNB is not widely recognised as standard care in early oral and oropharyngeal cancer.
However, increasingly it is gaining utility in Europe and in some countries, such as Denmark, it is integrated into the standard care pathway. Data emerging from this study are relevant to the evolving therapeutic use of SNB technique and provide data to support further investigation by prospective randomised trials. The drive towards patient-specific and minimally invasive
surgery is further refining the SN technique and we expect that the use of intraoperative 3D navigation [31], new tracers [32] and fluorescent markers [33] will improve the ease and accuracy of sampling sentinel lymph nodes. SNB potentially offers the solution to the dilemma ’How do you manage the N0 neck?’ Presentations of this work Part of this work has been presented by members of the Sentinel European Node Trial (SENT) group at meetings of the European Association of Craniomaxillofacial Surgery, The American Head and Neck Society, the
European Congress of Pathology, the International Association of Oral and Maxillofacial Surgery, and the British Association of Oral and Maxillofacial Surgeons as well as our annual SENT group meetings, part of the International Symposium on metastasis in head and neck cancer.

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