Sentinel Lymph Node Biopsy for Squamous Cell Carcinoma
- Author: Keith M Baldwin, DO; Chief Editor: Arlen D Meyers, MD, MBA more...
Introduction to Squamous Cell Carcinoma
Cutaneous squamous cell carcinoma (SCC) is a malignant tumor of keratinizing epidermal cells. This type of skin cancer is the second leading cause of skin cancer death after melanoma, and it is the second most common type of nonmelanoma skin cancer after basal cell carcinoma.
Most SCCs occur on the sun-exposed areas of the head and the neck. The most common route of spread for metastatic SCC is lymphatic in nature. In SCC of the upper aerodigestive tract, especially the neck, both the investigation and the treatment of a patient with a clinically N0 neck remain controversial. Depending on the classification of the tumor according to the TNM staging system, approximately 30% of patients with SCC of the head and neck have subclinical metastases in the neck, and knowledge of lymph node disease alters management.
Although CT scanning and MRI are commonly used to classify tumors of the neck, their overall accuracy is limited. The only highly accurate means of identifying lymph node disease is to perform a staging lymph node dissection. For disease in its early stages, clinicians are reluctant to perform an elective lymph node dissection because of the associated morbidity and lack of beneficial effects.
For more information, see Head and Neck Squamous Cell Carcinoma.
The sentinel lymph node
The sentinel lymph node (SLN) is the first lymph node to drain a metastatic tumor cell that drains via the lymphatic route. The concept of the SLN is based on the orderly progression of tumor cells within the lymphatic system. Mapping of the lymph flow from the tumor site to the regional lymphatic drainage area can be used to identify the primary draining lymph node (ie, SLN). If the SLN can be identified and examined for the presence of tumor metastases, an elective lymph node dissection for staging may not need to be performed.
The concept of the SLN originated in 1977 when Cabanas described mapping of the first lymph node–draining penile carcinoma. In 1977, Robinson et al described the use of cutaneous lymphoscintigraphy in the nodal basin for truncal melanomas using colloidal gold scanning. The development of lymphatic mapping at the end of the 1980s was a breakthrough in making the sentinel node concept applicable to various types of malignancies, particularly breast cancer and melanoma.
In 1993, Alex et al introduced the use of technetium-99m sulfur colloid, a radioactive tracer, which is injected intradermally around a primary melanoma site, followed by an imaging study and subsequent intraoperative use of a gamma probe to localize the sentinel node. Initial results of the SLN procedure in carcinoma of the head and the neck have been reported with mixed success. In a series of cases using radiocolloid alone, Koch et al remained unconvinced of its role in the management of patients with carcinoma of the head and neck. Pitman et al were unable to find any lymph nodes that stained blue in patients who were injected with blue dye alone. Alex and Krag performed the first successful SLN biopsy of the head and neck on a patient with a supraglottic carcinoma.
Incidence and prevalence of SCC
Approximately 100,000 cases of SCC are diagnosed in the United States each year. Approximately 80% of ultraviolet light–induced SCCs develop on the arms, head, or neck. The frequency of cutaneous SCC, as with all nonmelanoma skin cancers, is increasing.
Any of the following may cause SCC:
Exposure to sunlight
Chemical carcinogens, such as arsenic and hydrocarbons
Chronic irritation or ulceration
In addition, immunocompromised patients have a much higher risk of developing SCC. Two genes, PATCHED and TP53, have been identified that usually prevent cancers but are inactivated in patients with SCC; TP53 is mutated in more than 90% of patients with SCC.
SCC arises from basal keratinocytes of the skin. It typically manifests as a firm nodule on an erythematous base with elevated borders and insidious margins. Central ulceration or crusting may be present. Irregular nests of epidermal cells invading the dermis in varying degrees characterize SCC. Grading is based on the degree of cell differentiation. The most common route of spread for metastatic SCC is lymphatic in nature.
SCCs of the skin typically manifest on the head, neck, or arms. They usually have elevated and rolled edges with central ulceration. Well-differentiated SCCs are likely to manifest as firm erythematous nodules of varying sizes, sometimes with an area of central hyperkeratosis. The tumor is usually firm, although tumors in more advanced cases can be soft and friable. Erosion and ulceration are more common with SCCs. Poorly differentiated SCCs are more apt to manifest as faintly erythematous nodules or plaques that are not well defined; ulceration is also common.
Successful SLN biopsy
Defining a successful SLN biopsy accurately is critical. Although some studies have examined the impact of an individual surgeon's experience on the SLN identification rate, SLN identification is clearly not an appropriate endpoint; many studies have documented excellent SLN identification rates with unacceptably high false-negative rates. The more important issue is the experience required to achieve an acceptably low false-negative rate. In cases in which the pathology results from the scintigram are unclear or are negative, a formal elective neck dissection should be considered for staging purposes.
This procedure is multidisciplinary. As such, surgeons must ensure that nuclear medicine specialists, radiologists, and pathologists are actively involved with the successful implementation of this new technology. The learning curve for individual surgeons is undoubtedly associated with the experience levels of specialists within the multidisciplinary team. The implications of the SLN procedure must be effectively communicated to radiation oncologists and medical oncologists. The coordination of effort among the various specialists in each discipline is an essential component of the learning process.
The role of the SLN biopsy in the management of SCC of the head and the neck will evolve as more centers accept it as a potential standard of care.[5, 6, 7]
Indications for Biopsy in SCC
Elective dissection of a clinically negative (ie, N0) neck causes overtreatment for many early stage (T1, T2) patients, while no equivocal advantage in survival has been demonstrated when compared with a delayed dissection for patients with metastases in the neck in this group. SLN biopsy can help determine the presence of lymph node metastases in patients with T1-T2, N0 oral and oropharyngeal SCCs.
Contraindications for Biopsy in SCC
Contraindications to SLN biopsy are a palpable lymph node, tumors larger than 4-5 cm, disruption of lymphatic drainage, prior extensive surgery (eg, dissection of the neck), previous radiation to the head and the neck, and allergy to dye.
Contrast-enhanced CT scanning is helpful for determining the extent of tumor infiltration. Detection of grossly positive nodal disease, particularly when central necrosis is present, is increased with contrast-enhanced CT scans. The accuracy for detecting nodal metastases is reportedly improved from 70% to 93% when a physical examination is combined with CT scans, but occult disease can still be missed.
Fluorodeoxyglucose positron emission tomography (FDG-PET) is performed before removal of the primary tumor and/or dissection of the neck, and results are compared with those from histopathology studies. FDG-PET confirms the clinically identified location of the primary tumor site. FDG-PET shows promise in the initial staging of cancer of the head and neck. It also provides additional accuracy to the conventional staging process using CT scans.
MRI is beneficial for staging the size of the suggestive lymph nodes, for the evaluation of central lucency reflecting necrosis, for the assessment of irregular nodes with rim enhancement, for the evaluation of indistinct nodal margins, and for obliteration of fat or tissue planes.
The imaging studies are performed to detect any lymph node metastases. If the imaging studies fail to positively show lymph node metastases, an SLN biopsy is indicated for oral and oropharyngeal SCCs.
The current histopathologic routine is to step-section the SLNs at multiple levels and to perform immunohistochemical staining with S-100 protein and homatropine methylbromide to identify micrometastatic disease. If any question remains about abnormal cells after the first sections are taken, additional sections are obtained. Immunohistochemistry results identify an additional 10-20% of patients with positive SLNs, in whom micrometastases are not seen on routine sections stained with permanent hematoxylin and eosin (H&E). At least some of the increased rate of detection of micrometastatic disease is attributable to step-sectioning at multiple levels.
The approach for sampling involves bivalving the lymph node, fixing the 2 halves face down, and subsequently sectioning each half into 10 sections, which are alternately used for H&E staining, immunohistochemistry testing, and molecular staging. The sensitivity of intraoperative frozen section examination of the SLN is disappointingly low (< 50%), although false-positive results are almost never reported. Because of concerns about tissue loss during the frozen section procedure, most centers eschew frozen sections and rely on permanent sections, except to confirm grossly suggestive metastatic disease.
Patients undergo lymphoscintigraphy up to 1 day prior to surgery. A maximum of 40 MBq technetium-99m (99m Tc)-labeled human serum albumin (ie, AlbuRES, Nanocoll) is injected throughout the normal mucosa surrounding the tumor edge and the submucosa on the deep aspect of the tumor in a volume of approximately 0.5-1 mL. A syringe with a permanently secured needle is used for injection, thereby preventing inadvertent spillage of colloid into the mouth. Colloid is injected at as many points as necessary in an attempt to completely surround the tumor. A mouthwash is used immediately following injection to prevent pooling or swallowing of residual radioactive material by the patient.
Static lymphoscintigraphy is performed at 15 minutes, 30 minutes, and 1 hour postinjection in 2 planes or until the appearance of radioactive nodes. Hot spots are usually seen 15 minutes postinjection. If nodes are still absent 1 hour after injection, the lymph nodes are too close to the injection site or radiocolloid has leaked out of the injection site.
Either a cobalt-57 (57 Co) marker is used to trace the patient outline or a flood source of57 Co or99m Tc is placed behind the patient to produce a silhouette of the patient outline. In light of the radiation dose, the marker pen is preferable. A gamma camera fitted with a low-energy, general-purpose collimator is used to acquire images of the patient. A 20% window centered on the 140 keV photopeak is selected, and the camera is interfaced to a suitable computing system. The locations of radioactive lymph nodes are marked on the patient's skin, the position of a57 Co solid-source pen is observed on the camera's persistence display, and the pen is moved until its position overlies a radioactive node. This position is then marked on the patient's skin using indelible ink. During the skin marking, a lead plate of an appropriate thickness (eg, 3 mm) is used to shield the injection site.
Following image acquisition, a software mask is applied to all images to eliminate radioactivity from the injection site. A region of interest, drawn around the image of the site of injection, is used as the basis for the mask applied.
Two colloids are commonly used for lymphoscintigraphy: AlbuRES and Nanocoll. AlbuRES has a mean particle size of 500 nm and is a slower-moving particle that remains in first-echelon (sentinel) nodes but requires a high density of terminal lymphatic vessels at the injection site. For these reasons, AlbuRES is the colloid of choice on the tongue and on the floor of the mouth. Nanocolloid has a mean particle size of 50 nm and is a faster-moving colloid, which finds lymphatic vessels despite injection into tissues with low densities of terminal lymphatics. Nanocolloid also moves readily from sentinel nodes to subsequent-echelon nodes. For these reasons, nanocolloid is the colloid of choice for primary tumors that are not located on the floor of the mouth or on the tongue. Record the choice of colloid.
The overall success rate of a SLN biopsy by blue dye is 82%, by radioactive mapping is 94%, and by a combination of both is 98%.
Lymph node triangles of the neck
Lymph node groups of the neck region are divided into 2 triangles:
The anterior triangle
The posterior triangle
The anterior triangle of the neck is bounded anteriorly by the median plane, posteriorly by the sternocleidomastoid muscle, and superiorly by the base of the mandible. In addition, a line joins the angle of the mandible to the mastoid process. The apex of the triangle lies above the manubrium sterni.
The anterior triangle is subdivided by the digastric muscle and the superior belly of the omohyoid into the following:
The submental triangle
The digastric triangle
The carotid triangle
The muscular triangle
The submental triangle is the median triangle. On each side, the boundaries are the anterior belly of the corresponding digastric muscles. Its base is formed by the body of the hyoid bone. Its apex lies at the chin. The floor of the triangle is formed by the right and left mylohyoid muscles, with the median raphe uniting them.
The digastric triangle boundaries are, anteroinferiorly, the anterior belly of the digastric; posteroinferiorly, the posterior belly of the digastric and the stylohyoid; and superiorly (base), the base of the mandible and a line joining the angle of the mandible to the mastoid process. The roof boundary is the skin, superficial fascia, and deep fascia. The floor is formed by the mylohyoid muscle anteriorly and by the hyoglossus posteriorly and anteroinferiorly.
The carotid triangle boundaries are, superiorly, the posterior belly of the digastric muscle and the stylohyoid; anteroinferiorly, the superior belly of the omohyoid; and posteriorly, the anterior border of the sternocleidomastoid muscle. The roof boundary is skin, superficial fascia, and an investing layer of deep fascia. The floor is formed by parts of the thyrohyoid muscle, the hyoglossus, and the middle and inferior constrictors of the pharynx. Most of the SLNs are found in the carotid or the digastric triangle.
The muscular triangle includes the superficial structures in the infrahyoid region. The boundaries are, anteriorly, the anterior median line of the neck from the hyoid bone to the sternum; posterosuperiorly, the superior belly of the omohyoid muscle; and posteroinferiorly, the anterior border of the sternocleidal mastoid muscle.
The posterior triangle is a space on the side of the neck situated behind the sternocleidomastoid muscle. The boundaries of the posterior triangle are, anteriorly, the posterior border of the sternocleidomastoid muscle; posteriorly, the anterior body of the trapezius; and inferiorly (base), the middle third of the clavicle. The apex lies on the superior nuchal line where the trapezius and sternocleidomastoid muscle meet.
The posterior triangle is subdivided by the inferior belly of the omohyoid into the following:
The omohyoid triangle
The supraclavicular triangle
Lymph node dissection in both the omohyoid and the supraclavicular triangles in the posterior compartment is considered to be the same level.
Overview of SNL Biopsy
At operation, 1-2 mL of Patent Blue V dye may be used. To approximate the same injection sites as for radiocolloid, ensure that the same person performs all the injections. A suitable incision is made in the neck in such a position as to facilitate excision of the incision scar if a subsequent neck dissection is necessary.
The handheld gamma probe is used to identify radioactive sentinel nodes, including those marked preoperatively during lymphoscintigraphy. To reduce detection of radiation from the injection site, a series of malleable, sterilized lead plates may be used to mask the injection site, thus aiding in vivo identification of radioactive nodes. Radioactive nodes are excised, and radioactivity within the node is confirmed ex vivo.
If the blue dye is used, stained lymphatics, if seen, are followed to the first draining lymph node, which is then harvested. Sentinel nodes are labeled according to their color and radioactivity. The anatomic neck level of the sentinel nodes is noted. Although sentinel nodes are usually harvested prior to treatment of the primary tumor, the proximity of the sentinel node to the injection site may require a further search for sentinel nodes following excision of the primary tumor. If sentinel nodes are sought after excision of the injection site, the nodes are not likely to be stained blue.
Because of the relatively high radioactivity present in the injection sites and the proximity to the sentinel node, detection of scattered radiation must be avoided as far as possible. In addition to the use of the lead plates described above, the gamma probe must have a well-collimated detector, which excludes gamma radiation except over a small angle in front of it. Set the pulse-height analysis window to only include the99m Tc photopeak with a cutoff on the low-energy side at approximately 130 keV. Check the calibration at regular intervals of not more than 1 month (depending on the make and model of the instrument). Devise a quick check of calibration, and perform this quick check before each use. Calling on appropriate scientific or technical assistance may be necessary to ensure that the gamma probe is at its optimal settings and to make an estimate of its sensitivity at these settings.
Sentinel nodes are fixed in 10% neutral, buffered formalin, and, after fixation, they are bisected through the hilum (if identifiable) or through the long axis of the node. If the halves are thicker than 2 mm, the slices are further trimmed to provide additional blocks of 2 mm. If sentinel nodes are found to be free from tumor after the initial histologic examination, step-serial sections are prepared at an additional 6 levels in the block at intervals of approximately 150 µm. One H&E-stained section is prepared at each level. If the nodes still appear negative after histologic examination, an adjacent section from each level is examined by immunocytochemistry using the multicytokeratin antibody AE1/AE3.
Pathology Code Description
The interpretation of the histopathology and immunocytochemistry results for the SLN is categorized as stages 1 through 5.
Stage 1 tumor
In stage 1, the sample is positive for tumor upon first examination using H&E stain.
Stage 2 tumor
In stage 2, the sample initially appears negative for tumor, but it is noted to be positive for tumor upon examination of the H&E stain of step-serial sections.
Stage 3 tumor
In stage 3, the sample is negative for tumor at stages 1 and 2 but positive for tumor based on immunohistochemistry results. To be categorized as positive for tumor, cells must be present that are positive based on immunocytochemistry results and are cytologically observed to be nucleated cells with the characteristics of viable epithelial cells in both the immunocytochemical preparation and the serial H&E-stained sections. Cytokeratin positivity lacking the cytological features of viable tumor cells is categorized as stage 4.
Stage 4 tumor
In stage 4, cytokeratin positivity does not show the features of viable tumor cells. This positivity likely represents either dying tumor cells (possibly apoptotic cells), characterized by eosinophilic bodies lacking normal nuclei, or macrophages with phagocytosed tumor products. Usually, these cells are single and not in small, cohesive groups. The decision to allocate nodes to this category requires careful comparison of the serial H&E-stained section and the immunocytochemical preparation.
Stage 5 tumor
The sample is negative for tumor at all stages.
Approach After Staging
If any lymph node contains a viable tumor (ie, stages 1-3 according to the pathology code description) either based on routine histology studies or based on immunohistochemistry and multiple sectioning, the patient undergoes a radical or modified radical dissection of the neck. Perform the dissection of the neck within 4 weeks of the SLN biopsy, and begin any adjuvant radiotherapy within 6 weeks of the dissection. Do not administer radiotherapy prior to a neck dissection.
For tumors in stage 4 or 5 according to the pathology code description, no further treatment to the neck is required and no prophylactic neck radiotherapy or additional surgery is necessary.
The current treatment for patients with squamous cell carcinoma includes a proper diagnosis based on a high level of consideration and examination, with subsequent staging and development of a treatment paradigm. A treatment program of surgery, radiation, or chemotherapy is best developed by an oncology team that includes surgeons, radiation and medical oncologists, and rehabilitative specialists who all have significant experience in the care of patients with cancer involving the head and the neck. By using this approach, new protocols and surgical options can be appropriately offered to those patients with advanced cancers.
Outcome and Prognosis
The sentinel lymph node (SLN) biopsy can be a valuable staging technique for patients with squamous cell carcinoma whose lymphatic drainage of the neck has not been altered by previous surgery or radiotherapy. It provides reliable detection of micrometastasis, indicating which levels should be removed ipsilaterally or contralaterally. This technique also allows the surgeon to accurately plan a dissection of the neck, taking into consideration the pattern of lymphatic drainage of each patient. In this way, unnecessary dissection of the neck and its morphofunctional sequelae can be avoided in numerous patients.
The cumulative results of all those who contributed to the first international conference on SLN biopsy of mucosal cancer of the head and the neck confirm that SLN biopsy has a role in staging the clinically N0 neck, and it has a similar sensitivity to that of a neck dissection for staging.
Complications of SLN Biopsy
Allergic reactions to isosulfan blue, nerve injury, lymphedema, neuropathy, fat necrosis, seroma, and hematoma can result following dissection of an SLN.
Patients are seen every 3 months for the first year, every 4 months for the following 2 years, and every 6 months until 5 years following SLN biopsy. At any stage, if nodal disease is detected, patients can elect to undergo surgical treatment of the neck.
Sentinel lymph node (SLN) biopsy for head and neck squamous cell carcinomas (SCCs) is assuming a growing role in the management of early-stage patients. Particularly, those with T1 and T2 tumors may benefit from the procedure since the rate of occult lymph node metastases in this group is much lower than more advanced tumors. The accuracy of identification and false-negative rates of the procedure are good, but if there is concern by the surgeon performing the procedure that the node is difficult to locate (ie, lymphoscintigraphy findings are unclear or it is difficult to identify in the operating room), a formal neck dissection should be performed. SLN biopsy will probably play an increasing role in the management of early-stage head and neck SCC in the future.
Alex JC, Weaver DL, Fairbank JT, Rankin BS, Krag DN. Gamma-probe-guided lymph node localization in malignant melanoma. Surg Oncol. 1993 Oct. 2(5):303-8. [Medline].
Koch WM, Choti MA, Civelek AC, Eisele DW, Saunders JR. Gamma probe-directed biopsy of the sentinel node in oral squamous cell carcinoma. Arch Otolaryngol Head Neck Surg. 1998 Apr. 124(4):455-9. [Medline].
Pitman KT, Johnson JT, Edington H, Barnes EL, Day R, Wagner RL, et al. Lymphatic mapping with isosulfan blue dye in squamous cell carcinoma of the head and neck. Arch Otolaryngol Head Neck Surg. 1998 Jul. 124(7):790-3. [Medline].
Alex JC, Krag DN. The gamma-probe-guided resection of radiolabeled primary lymph nodes. Surg Oncol Clin N Am. 1996 Jan. 5(1):33-41. [Medline].
Dequanter D, Shahla M, Paulus P, Lothaire P. Long term results of sentinel lymph node biopsy in early oral squamous cell carcinoma. Onco Targets Ther. 2013. 6:799-802. [Medline].
Yoshida Y, Shiomi T, Tahira M, Yamamoto O. Metastatic basosquamous carcinoma detected by sentinel lymph node biopsy. J Dermatol. 2013 Jun 3. [Medline].
Govers TM, Hannink G, Merkx MA, Takes RP, Rovers MM. Sentinel node biopsy for squamous cell carcinoma of the oral cavity and oropharynx: A diagnostic meta-analysis. Oral Oncol. 2013 May 13. [Medline].