Sentinel Lymph Node Biopsy using Methylene Blue Alone in an Era of Significance of the Depth of Invasion in Oral Cancers

A Prospective Study

Abstract

Aim: 

To evaluate the accuracy of methylene blue dye alone in identifying sentinel nodes in oral cancers with clinically N0 neck and the significance of the depth of invasion (DOI) in combination with sentinel lymph node (SLN) biopsy in predicting nodal metastasis.

Methods: 

This is a prospective study done over 24 months accruing 67 patients with cN0 neck admitted to our center for oncology. SLN harvesting was done adhering to the standard procedure using methylene blue dye for all early-stage oral cavity cancers with N0 neck clinically. Data were collected, grouped, and analyzed for deducing DOI, sensitivity, specificity, positive predictive value, and negative predictive value of the procedure and compared with other studies in the literature.

Results: 

Out of 67 patients, males (76.1%) outnumbered female (23.9%) patients. The mean age of the patients was 51.5 years. Tongue (61.2%) was the most common site. Sentinel nodes were identified in 89.5% of patients. The mean number of Sentinel nodes identified was 1.9. The mean DOI was 7.3 mm. SLNs were most commonly identified in Level I (78.3%). Sensitivity, specificity, positive predictive value, and negative predictive value and accuracy deduced in this study were 75%, 97.9%, 90%, 94%, and 93.3%, respectively.

Conclusion: 

Methylene blue dye alone can be successfully used for SLN identification in clinically node-negative oral cavity cancers, particularly with less DOI. DOI alone for predicting nodal involvement can be used with caution. Combination of DOI and sentinel node biopsy may help in better identification of nodal involvement.

INTRODUCTION

Oral cavity carcinoma is considered an important part of the global burden of cancer mainly due to the widespread use of tobacco and alcohol.[¹] Cervical lymph node involvement results in a 50% decrease in survival and the possibility of distant metastases increases.[²] Hence, cervical node involvement is an important prognostic indicator in oral cavity cancer. Elective neck dissection (END) is the current gold standard for staging the cervical lymph nodes in the carcinoma oral cavity.[³] This procedure is both staging and therapeutic, which has potential benefits for patients who are subsequently found to have an occult disease. It has been routinely used in the surgical management of head-and-neck malignancy where the risk of occult metastases is significant (>20%). These procedures are associated with increased morbidity.[⁴] However, occult disease is present in 25% of the patients, leading to overtreatment in the remaining 75%.[⁵] Depth of invasion (DOI) is associated with a higher incidence of regional failure, but still has poor sensitivity and specificity for nodal involvement.[⁶]

Sentinel lymph node biopsy (SLNB) allows for staging of the cervical lymph nodes with minimum morbidity compared to that of END.[⁷] The dual technique of lymphoscintigraphy with radiolabelled particles and gamma probe localization combined with a blue dye injection is used commonly for SLNB.[⁸⁹¹⁰] However, lymphoscintigraphy and gamma probe localization are not easily available in all centers.[¹¹] Therefore, alternate techniques for sentinel lymph node (SLN) identification need to be evaluated.

Methylene blue is an affordable, easily available, less allergic, and effective dye showing good results in SLN studies in breast cancer when used alone or in combination with lymphoscintigraphy.[¹²¹³¹⁴] In this study, we evaluated the feasibility of using only methylene blue dye in identifying sentinel nodes in oral cancers with clinically N0 neck and the significance of the DOI in combination with SLNB in predicting nodal metastasis.

METHODS

This is a prospective study done from 2018 to 2020, in which 67 patients with cN0 neck were accrued by the inclusion of patients fulfilling desired eligibility criteria in our center for oncology. Primary was evaluated clinically and with contrast-enhanced computed tomography magnetic resonance imaging from the base of the skull to neck whenever required and staged according to American Joint Committee on Cancer 8^th Edition. Negative nodal status was confirmed clinically which included ultrasound neck. Informed consent was obtained from all patients. Just before making an incision, methylene blue dye was injected all around the tumor, subplatysmal flaps were raised and blue nodes dissected and sent for frozen. Neck dissection was continued with a minimum of selective neck dissection (SND) (extended supra omohyoid neck dissection [ESOHND] for tongue primary and supra omohyoid neck dissection [SOHND] for rest of subsites) if frozen was negative or modified radical neck dissection (MRND) if frozen was positive. The final specimen was sent for histopathological examination. All specimens were examined by serial sectioning with 2 mm cuts. The postoperative histopathology reports were analyzed for confirming the diagnosis, nodal status, and evaluation of DOI and grade/differentiation of disease.

Eligibility criteria

Inclusion criteria

Oral cavity cancers with no clinically palpable lymph nodes.

Exclusion criteria

1. Recurrent disease
2. Clinically and sonologically node-positive cases
3. Patients allergic to the dye
4. Patients with previous neck surgery/radiation.

• Informed consent was obtained from all patients
• Just before making incision 0.5 ml of 1% methylene blue was injected around the tumor at 4 sites (total 2 ml)
• The time duration between the injection of dye and raising neck flaps will be 10–15 min
• Blue-stained lymph nodes were dissected out identifying the level and sent for frozen section
• In SND nodal tissue was excised in total separately, whereas in MRND en bloc dissection along with primary was done in continuity.

RESULTS

There were 67 patients out of which 51 (76.1%) were male patients and 16 (23.9%) were female patients. The age of the patients was in the range of 30–80 with a mean age of 51.5 years. The tongue was the most common site involved, seen in 41 (61.2%) patients, followed by buccal mucosa in 17 (25.3%) patients, retromolar trigone in 4 (6%) patients, floor of the mouth in 1 (1.5%) patient, alveolus and hard palate in 2 (3%) patients each. Out of 67 patients T1 lesion was seen in 17 (25.3%) patients, T2 lesion in 40 (59.7%) patients, and T3 lesion in 10 (15%) patients. Well-differentiated lesion was seen in 41 (61.2%) patients and moderately differentiated lesion was seen in 25 (37.3%) patients and poorly differentiated lesion was seen in 1 (1.5%) patient. Thirty-six patients (53.7%) underwent ESOHND, 21 (31.3%) patients underwent SOHND and 10 (15%) patients underwent MRND, as shown in [Table 1].

Table 1: General characteristics

Sentinel nodes were identified in 60 (89.5%) out of 67 patients. The number of Sentinel nodes identified was in the range of 1–5, with a mean of 1.9. Majority of sentinel nodes were identified in Level I in 47 (78.3%) patients, followed by Level II in 7 (11.7%) patients and Level III in 6 (10%) patients, as shown in [Table 2]. DOI was in the range of 4 mm–15 mm, with a mean of 7.3 mm, as shown in Table 2. Sentinel nodes were not identified in Level IV and Level V. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy value was 75%, 97.9%, 90%, 94%, and 93.3%, respectively, as shown in Table 3. Out of the 12 patients with nodal disease, five patients had T3 lesion (50% of T3) with DOI >10 mm and seven patients had T2 lesion (17.5% of T2) with DOI of 5–10 mm. None of the patients with DOI <5mm had positive nodes, as shown in [Table 4 and Figure 1].

Figure 1: Scatter plot showing correlation between DOI and SLN positivity. DOI: Depth of invasion, SLN: Sentinel lymph node

Table 2: Distribution of sentinel lymph nodes

Table 3: Statistical analysis

Table 4: Correlation of depth of invasion and sentinel lymph node positivity

DISCUSSION

The incidence of nodal metastases in oral cavity malignancies depends on the size of disease, subsite, depth of infiltration, differentiation, etc., and varies between <10% and up to 50%.[¹⁵]

Management of the clinically negative neck in patients with carcinoma oral cavity is controversial. Choosing between END and wait-and-see policy based primarily on the characteristics of the primary tumor is a risky proposition[¹⁶] because approximately 25% of clinically negative patients are reported to harbor occult metastases.[¹⁷¹⁸] Conversely, END for all patients is not justified because of associated morbidity.[¹⁹]

SLNB is not the standard of care in oral cavity cancers.[²⁰] However, many single-institution studies[⁸⁹¹⁰] and two multi-institution studies[²¹²²] have validated it in oral cancers with high detection rates (around 95%) and negative predictive values (88%–100%). In our study, the detection rate was 89.5% and the negative predictive value was 94%. Three meta-analyses by Paleri et al.,[¹¹] Govers et al.[¹²] and Thompson et al.[¹³] based on pooled data samples have also confirmed its use in the staging and treatment of early-stage head-and-neck cancers.

The dual technique of lymphoscintigraphy with radiolabelled particles with gamma probe localization and blue dye injection is used in the majority of studies where ever facilities are available.[⁸⁹¹⁰] Lymphoscintigraphy and gamma probe facilities are not widely available,[²³] leaving methylene blue dye alone as the widely used and easily available method. Methylene blue alone for SLN identification has provided equal or slightly inferior results compared to dual techniques in breast cancer.[²⁴²⁵²⁶] Similar studies in oral cancer are very few.[²⁷²⁸]

In our study, sentinel node detection rate was 89.5% which was similar to that of Ramamurthy et al.[²⁷] study (90.6%). In our study, sentinel nodes were seen in Level I in 47 (78.3%) patients, followed by Level II in 7 (11.7%) patients and Level III in 6 (10%) whereas it was 54.3%, 37.1%, and 8.6%, respectively, in Vishnoi et al.'s[²⁹] study. Sentinel nodes were not identified in Level IV and V in any subsite. Shah[³⁰] reported similar findings for early cancers of the buccal mucosa. However, Woolgar[³¹] and Byers[³²] reported 15.8% skip metastasis to Level IV in patients with carcinoma tongue.

Sensitivity in our study was 75%, whereas it was 80% in Ramamurthy et al.[²⁷] study and 84.6% in Vishnoi et al.'s[²⁹] study. Specificity and negative predictive value were 97.9% and 94%, respectively, whereas both were 95.8% and 95.8% in Ramamurthy et al.[²⁷] study; the negative predictive value was 93.9% in Vishnoi et al.'s[²⁹] study. Sensitivity and negative predictive values were 86% and 95%, respectively, in Schilling et al's.[³³] study where both lymphoscintigraphy and blue dye were used. Accuracy in our study was 93.3%, whereas it was 95.5% in Vishnoi et al.'s[²⁹] study.

Out of the 12 patients with nodal disease in our study, five patients had T3 lesion (50% of T3) with DOI >10 mm, and seven patients had T2 lesion (17.5% of T2) with DOI of 5–10 mm. None of the patients with DOI <5 mm had positive nodes. Huang et al.[³⁴] and Pentenero et al.[³⁵] conclude that DOI correlates with regional lymph node involvement. Both studies found a wide range for cut-off values of 1.5–10 mm, with a most optimal cut-off value of 4 mm in the meta-analysis of Huang et al.[³⁴] Goerkem et al.[³⁶] found an average DOI of 6.45 mm, concluding that DOI (and separately also tumor thickness) should not be used for assessment of END. Moreover, they suggested that SLNB should be used in all early-stage oral cavity carcinomas with a cN0 neck.[³⁶]

Limitations of using methylene blue dye alone for SLNB include mandatory elevation of the neck flaps before SLN identification. In the case of lymphoscintigraphy, the size of the neck incision can be minimized over hot spots before extending it for formal neck dissection. Other drawbacks are the inability to evaluate the contralateral neck, spillage of dye into surrounding tissue obscuring elevation of proper tissue planes, and the chance of missing some deeper nodes.[²⁷]

Limitations of the frozen section include errors of sampling and errors of interpretation. These include the initial selection of tissue by the surgeon, sampling of the tissue by the pathologist, preparation of slides, errors in interpretation, and delivery of the result back to surgeons.[³⁷³⁸] Quality of prepared sections during cryostat sectioning plays an important role in frozen section diagnoses.[³⁹] The use of frozen section with limitations in mind makes it a highly sensitive and specific technique playing a critical role in the management of patients.[⁴⁰]

In our study, the three patients with false-negative reports received 50Gy adjuvant radiotherapy and are on close follow-up. This technique should be evaluated in large multi-institutional studies for standardization, which will be of immense use in centers where adequate lymphoscintigraphy facilities are not available.

CONCLUSION

Methylene blue dye alone can be successfully used for SLN identification in clinically node-negative oral cavity cancers, particularly with less DOI. DOI alone for predicting nodal involvement can be used with caution. Combination of DOI and sentinel node biopsy may help in better identification of nodal involvement.

Ethical committee approval

Institutonal Ethics Committee of Govt. Kilpauk Medical College Protocol ID. No: 289/2019 dated on 05/12/2019.

Declaration of patient consent

The authors declare that they have obtained consent from patients. Patients have given their consent for their images and other clinical information to be reported in the journal. Patients understand that their names will not be published and due efforts will be made to conceal their identity but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.