Discusión

Preliminary study of the sentinel node in oral cancer:
in conjunction with 12 cases
Estudio preliminar del ganglio centinela en el cáncer oral: a propósito de 12 casos

It is awarding to verify that the cervical staging technique by cervical sentinel node (SN) biopsy in head and neck squamous cell carcinoma (HNSCC) awakens interest and concern within our Speciality and I believe that we should congratulate the Authors of this study, source of a more ambitious project. During recent years, the articles that have been appearing in the English literature have been multiplying, demonstrating the reliability of the technique for this type of tumors. However, the lack of studies published in Spanish- speaking journals, both in our speciality as well as other similar ones dedicated to head and neck surgery is of concern.

Although the presence of cervical lymph node metastasis is the factor having the greatest prognostic value in HNSCC,^1,2 most of the prophylactic cervical dissections in patients with cervical stage N0 (40-85%) are unnecessary and involve and overtreatment.^3,4 The cervical staging technique by detection and biopsy of the cervical sentinel nodes (SN) makes it possible to reduce morbidity suffered by patients having these terrible tumors and, in addition, it not only equals, but also can increase the safety and accuracy of their cervical staging.^5,6 This is due to its capacity to improve preoperative identification of aberrant lymph drainage patterns, which makes it possible to increase histopathological study efficacy and sensitivity, on selecting the cervical lymph nodes with the greatest likelihood of finding metastatic foci.

The present study tries to validate the cervical staging performed through the detection technique and biopsy of the cervical SN in oral squamous cell carcinomas by a prospective study. The results obtained are excellent with a 100% sensitivity (absence of false negatives or fugitive metastatic lymph nodes, defined as those found in the cervical dissection specimen when all the SN are negative) that demonstrate a total agreement between the cervical staging performed with the SN biopsy technique and the staging obtained after the histological study of all the cervical dissection specimen. This implies that when the SN biopsy technique is used exclusively, no errors will have been made in the cervical staging of any patient and 9 unnecessary (82%) cervical dissections would have been avoided, with the consequent reduction in morbidity and economic cost.

The authors include patients with exclusively oral carcinomas, excluding the oropharyngeal ones in the interest of, I understand, its greater accessibility for the correct peritumoral injection of the radiotracer. Attention is called to the non-exclusion of tumors based on their T stage. In our experience,⁶ the most probable source of errors (false negatives) is the incorrect peritumoral injection of radiotracer around very large tumors, due to the difficulty that it has, causing the spreading of it through lymph drainage pathways other than those that would have truly followed the neoplastic cells of the tumor. Only the small tumors in T1 and T2 stage allow, in my opinion, there to be the certainty of performing the tumor injection correctly, although it may also be performed in small sized T4 tumors (its stage as such, T4, is due to the simultaneous involvement of adjacent regions).

During the lymphoscintigraphy (LCG), the authors consider the study to be completed on detecting, I understand, the first SN or at 24 hours after the radiotracer injection. In our experience, and perhaps motivated by the rich head and neck lymphatic drainage, the appearance not only of a SN but generally of several almost always occurred within the first 5-10 minutes after the injection. The authors comment in the discussion that the SN was always detected in the dynamic phase of the LCG that they performed for 15 minutes. They do not reflect in their study if they recorded the posterior appearance of the radioactive SN during the dynamic phase (considered by us as primary SN)⁶ or the static phase of the study (secondary SN). The explanation to this difference could be found in the use of a radiotracer with a different particle size. While we have always used a sulfur colloid with a particle less than 50 micras (Lymphoscint^®), in this study, the authors used a nanocolloid in which, although they do not mention its composition, the particle is, by definition, a little larger (50-80 micras).

The repetition of the radiotracer peritumor injection 2 hours prior to the surgery confuses me as I have no reference of any work group that uses this methodology. I suppose that the objective of this is to potentiate the radioactivity emitted from the SN in order to facilitate its identification during the surgical act. The SN biopsy technique is a procedure that is not totally standardized and that is in continuous evolution, development, and improvement. Our experience tells us that the lymphoscintigraphy (LSG) should be performed whenever possible on the same day of the surgery in order to be more selective with the number of SN identified.⁶ This implies, however, an unadvisable delay in the onset of the surgical intervention in this type of patients in our hospital. On the contrary, when the LSG is performed the day before the surgery, on examining the surgical bed with a gamma probe, we find that some cervical lymph nodes that were cold the day before (not radioactive) have become warm or radioactive. The explanation to this phenomenon, that may hinder the identification of the true SN, is no other than the dynamic and continuous physiological process of cervicofacial lymph drainage that causes the migration of certain radiotracer amounts of some lymph nodes to others during the period between the LSG and the surgery. The double injection of radiotracer, the previous day and the same day of the surgery, to my understanding, does not contribute clarity, but rather confusion to the selective detection of the SN, although it should be the authors of this study who, in the future, show us the advantages and disadvantages of this new method.

During the surgical phase, the authors consider as SN, and only obtain, the lymph node with greater radioactivity of each cervical level although several radioactive lymph nodes exist in it. This could lead to errors in the diagnosis of the SN on overlooking the migration of the radiotracer during the interval between the LSG and surgery. Our attitude has been the excision of all the radioactive nodes once their approach is performed, since, due to the migration suffered by the radiotracer, it may occur that the radioactivity from the true SN is less than that of other adjacent ones that have received amounts of radiotracer during this period. It is a relatively frequent to find radioactivity values greater that that of the SN considered as primary in SN of lower cervical lymph node levels which were considered as secondary during the LSG.

It is also surprising that the authors have been able to identify all the SN detected in the LSG in equal number and position during the surgery and that this is single in 10 of the 11 patients We⁶ have never obtained this effectivity rate to determine and isolate a single SN, it being usual^5,7,8 to find more than 1 SN (range between 2 and 5 SN per patient with an average of 3.5 SN) and to isolate more SN (even on the same cervical lymph node level) during the surgery than during the LSG (especially when the LSG is performed the day before the surgery) due to the simple physiological fact of the continuous migration of the radiotracer through the lymphatic channels during the time between both events or perhaps because the spatial resolution of the LSG does not make it possible to discriminate the presence of several SN on a same cervical level.

The consideration of a certain number of counting from which a SN is considered warm or radiopositive has been described in many articles, one copying from the other. In our experience with several gamma surgical probes, the radioactivity coming from the cervical bed is practically nonexistent and that which comes from the SNs fundamentally varies based on the time between the injection (after a period equal to the half life of ⁹⁹Tc, the radioactivity is reduced, by definition, to half) and the greater or lesser lymph node distribution of it, without being able to determine for sure threshold value or values.

The authors do not use the mixed identification technique (injection of radiotracer prior to the LSG and blue stain prior to the surgery), perhaps based on the different studies that show that while the uptake of the radiotracer by the SN is very predictable, that corresponding to the blue vital stain is not so predictable. I consider this a correct decision, above all in order to prevent all that which makes the correct resection of the primary one difficult and avoids its possible side effects (anaphylactic reactions and permanent stainings).

In short, this study demonstrates again that in the treatment of patients with oral and oropharyngeal squamous cell carcinomas with N0 clinical neck staging, the detection technique and cervical sentinal node biopsy constitute an elegant intermediate solution between the waiting attitude (no treatment) and cervical disection.^5,6,9 Using a minimally invasive biopsy and histopathological study of the SN, a even more exact cervical staging can be achieved than by the standard pathological study of all the cervical dissection specimen, making it possible to identify the patients, in the N0 clinical-radiological stage, who truly require the performance of a cervical dissection. I believe that the time has arrived to take one step forward, no longer validating that already validated, and entering to form a part of the group of European head and neck surgeons (European project of the EORTC, European Organization for Research and Treatment of Cancer, Head and Neck Cancer Group) that have already used the detection and biopsy of the cervical SN for years as standard method (besides the clinical examination) to perform the cervical staging of the patients suffering from oropharyngeal squamous cell carcinomas, thus avoiding unnecessary cervical dissections.

Dr. Pedro Mª Villarreal Renedo
Servicio de Cirugía Oral y Maxilofacial
Hospital de Cabueñes. Gijón, Asturias.

References