The first article in this series discussed advances in endoscopic skull base surgery. Another new technology that is being developed for head and neck cancer surgery is the use of sentinel node biopsy for oral squamous cell carcinoma.
Sentinel node biopsy is a patient-driven phenomenon as well as a physician-driven phenomenon. People want you to do the same thing or get the same information while causing fewer side effects, explained Francisco J. Civantos, MD, Associate Professor of Head and Neck Surgery at the University of Miami in Florida.
We are hearing a lot about less-invasive ways to resect primary tumors-for example, laser surgery for hypopharyngeal and supraglottic tumors-and it would also be nice to also be able to apply less-invasive techniques to the neck, he said.
Dr. Civantos said that sentinel node biopsy is a diagnostic procedure, not a therapeutic one. The goal of the procedure is to identify who needs the larger operation and who doesn’t. It offers us the option where someday we may be doing a supraglottic resection of a cancer of the larynx and then doing a sentinel node biopsy and not having to radiate or worry about the neck nodes or do extensive dissections after we have taken out this little tumor endoscopically.
However, sentinel node biopsy for tumors of the oral cavity is different from sentinel node biopsy for melanoma or breast cancer, he said. The first question is proof of principle of whether injecting radionucleotide in the mouth will truly allow you to harvest the proper node and predict the status of the neck.
There are some differences when treating the oral cavity. Blue dye makes things messy and interferes with visualization. Nobody who does sentinel node biopsies for mucosal lesions uses blue dye, Dr. Civantos said in his lecture at the Combined Otolaryngology Spring Meeting last May. But the concept of having a second agent that will help with issues of background activity at the primary site is a good one. There is a new product called Sonozoid that may actually allow us to replace blue dye with an ultrasound-visible agent that can be injected into the primary site and allow us to deal with issues at the primary site. This is very preliminary and blue dye still works, but we haven’t used blue dye in our patients for sentinel node biopsy for oral cancer.
In sentinel node biopsy, he said, the primary tumor is injected with a tracer fluid. Nuclear imaging is employed to map the lymphatic drainage and indicate the location of the sentinel node. A gamma probe measures radioactivity in the neck and identifies the hot node, directing the surgeon to the location and subsequent removal of the sentinel node. If histology indicated the sentinel node is negative, then it precludes the necessity for cervical lymphadenectomy.
A percentage of patients with early stage squamous cell carcinoma in the oral cavity will have microscopic spread of cancer to the lymph nodes, he said. The majority of patients who do not truly need treatment to the neck are treated in order to catch the ones who truly need treatment.
Whereas in breast cancer and melanoma one to three sentinel nodes is the norm, in head and neck cancer, due to lymphatic drainage patterns, Dr. Civantos said three or four sentinel nodes are likely to be detected. We dissect any node that is up to 10% as hot as the hottest node.
When do you know if you have a histologically negative sentinel node? If the sentinel node is abnormal we will get a frozen section, but otherwise, there will be step sectioning and immunohistochemistry, he said. You want that done quickly so you can re-explore if the patient has a positive node before inflammation sets in the head and neck. The histology can be turned around in three days so you can re-explore the patient if you find a positive node.
Candidates for Sentinel Node Biopsy
Dr. Civantos said that the sentinel node biopsy procedure should be attempted in a patient population in which most of the individuals would be expected to have negative nodes. If the procedure is attempted on later-stage patients, he said the procedure would not be warranted. If you need to reoperate on 50 percent of the patients, then this technique does not make any sense. It is a great technique if you select a population at low risk-perhaps patients who, in the past, would have been candidates for a watchful waiting approach, he suggested.
In our trial we did have patients with minimally invasive tumors who did have positive sentinel nodes and those are patients who might have been treated with a watchful waiting approach in many people’s hands, he said. Seventy to 80 percent of the patients we are treating with neck dissection don’t need it. [But] if your patients did need it and you refer to watchful waiting, there is a lower chance of cure.
Details of the Trial
Dr. Civantos said the Z0360 protocol involved 34 investigators from 25 institutions. It was a very simple protocol that duplicated the validation trials that were done for melanoma and breast, he said. Basically patients with resectable T1 or T2 early oral cancers underwent preoperative injection of radionucleotide and radiolymphoscintigraphy, followed by resection of the primary tumor. Through a smaller incision, we attempted to mimic sentinel node biopsy in the true setting using gamma probe guidance. The incision was then extended and a selective neck dissection was then performed.
We concluded that the sentinel node biopsy technique is valid in principle for oral cavity cancer in the sense that if you inject you do get mapping to the appropriate lymph node, Dr. Civantos said. We need to define the population to whom we want to apply this. Given the limitations of this model in reproducing a true sentinel node biopsy, we still recommend caution. We must document local recurrence rates in the neck after sentinel node biopsy alone.
Strategy for Using Sentinel Node Biopsy
He said that doctors who are considering using the sentinel node biopsy strategy should approach the practice carefully. Nobody should just start doing this procedure, he said. The way to get into this is to start injecting, getting a map, and taking out sentinel nodes and then continuing with a selective neck dissection. Essentially, after some initial instruction, you develop expertise through this technique. The combination of sentinel node biopsy with selective neck dissection allows you to upstage patients and to map the lymphatics so you can do a more thorough neck dissection. At the same time you can develop expertise in the minimally invasive procedure.
You want to counsel your patients regarding the potential for re-exploration and talk to them about which way they would rather go. You want to counsel them about the small risk of false negatives and that they do need to be followed, he said.
Dr. Civantos noted that there have been more than 60 single institutional studies of sentinel node biopsy for oral cancer; 200 international conference documents have been reported; a meta-analysis has been published; and a European multi-institutional study has also been reported. All these studies have reported predictive values of 90 percent to 100 percent, meaning that if you get a negative sentinel node there is a less than 5 percent chance of missing cancer. You combine that with a group that already has low risk to begin with and it can be safe and give you a little bit of reassurance, he said.
The major concern had been related to the fact that a false negative in a highly curative patient is a big deal, and we are more nervous about the watchful waiting approach, so we should be cautious about sentinel node biopsies, too, he said.
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