A New Technology for Sentinel Node Biopsy: A Logistic Improvement
It has become increasing apparent that surgical treatment of breast is becoming less invasive. With fewer indications for complete axillary node dissection, however, sentinel node biopsy remains the reference-standard technique to give clinicians important information to make treatment decisions with acceptable minimal morbidity. Even in the face of improved molecular profiling to direct breast cancer care, axillary staging remains an important diagnostic, prognostic, and local control procedure in the treatment of breast cancer. Sentinel lymph node biopsy is not going away in the near future. Therefore, new technologies to improve the methods to perform this procedure and to decrease the risk for patients are important to explore. The traditional methods of identifying sentinel node biopsy include vital blue dye and or a nuclear tracer such as technetium 99m (Tc-99m) sulfur colloid. Both methods have limitations. Vital blue dye alone is logistically easier to use. It is injected in the operating room when the patient is asleep, and it is under the complete control of the surgeon. However, identification rates are lower with blue dye alone, and it is associated with rare but serious allergic reactions or skin necrosis.1, 2, 3, 4, 5 Many surgeons utilize with good success nuclear tracers alone.6,7 Logistically, its utilization is more complicated. In many hospitals, licensing issues prevent injection in the operating room, and patients must go to the nuclear medicine department ahead of time for both the injection and imaging maps, a time-consuming procedure. Additionally, both patients and providers are exposed to radiation. Finally, there may be access issues in rural and smaller communities to the nuclear tracer, as evidenced by an analysis of the Surveillance, Epidemiology, and End Results data showing fewer sentinel node procedures being performed in rural compared to urban areas, possibly because of a shortage of experienced surgeons, lack of training, or lack of technological support at smaller institutions. Many of the smaller community hospitals may not have access to the equipment needed to perform sentinel lymph node biopsy, such as nuclear medicine facilities; nor may radiolabeled tracer and trained surgeons be available.8
An article in this month’s Annals of Surgical Oncology analyzes data from five European trials utilizing a magnetic tracer to identify sentinel nodes.9 Lymphatic mapping is most often performed using radioisotope with or without blue dye (standard tracers). Sienna+, a superparamagnetic iron oxide that can be detected using the sentimagmagnetometer, is an alternative mapping agent to identify sentinel lymph nodes that has been investigated in five clinical trials. This meta-analysis was performed to determine if Sienna+ is noninferior for SLN detection compared to standard tracers. The investigators showed that Sienna+ was noninferior to standard methods. The difference in detection rate per node between Sienna+ and the standard tracer technique was estimated to be 5.5 % (95 % confidence interval 2–8.9), favoring Sienna+. The difference in detection rate per patient between the Sienna + and standard tracer techniques was estimated to be 0.2 % (95 % confidence interval −3.7 to 4.2). There was less concordance in negative nodes, with the Sienna + method identifying more nodes overall. Most importantly, there was extremely high concordance in patients with positive nodes.
The magnetic tracer has similar advantages to the blue dye technique; for example, the tracer is injected in the operating room when the patient is asleep. It is under the control of the surgeon; therefore, there are fewer logistical issues and it is more convenient for both surgeons and patients. Last, there is no radioactivity involved, with its associated risks. As with all methods, there are limitations. Because the detection system uses a magnetometer, metal instruments will cause false-positive results and cannot be used. Disposable plastic instruments are available for use, but they can be challenging in obese patients with a deep axilla. Some patients experience brownish skin discoloration, which is less noticeable than the blue coloring from isosulfan blue. Finally, the Sienna + is an iron oxide originally developed as an MRI contrast, and as such, it may remain in the breast tissue, potentially interfering with postoperative MRI.
As with any metaanalysis, analysis of the data has limitations because the studies were designed differently and different data points were collected in some studies. Thus, there are some incomplete data. For example, not all studies used blue dye in addition to radioactive colloid, or injection of blue dye was left to the discretion of the surgeon. Therefore, detection rates using blue dye are missing in some studies. The authors account for the heterogeneity of the studies in their analysis and still conclude that the magnetic tracer is noninferior. The provide the statistical analysis necessary and make it understandable. It is reassuring to see that when the nodes are positive, there is high concordance. Whether it is good or bad to take out one or two extra negative sentinel nodes is debatable, but both methods can accurately identify positive nodes—the crux of the issue. The authors also point out that another single-arm trial in the United States was recently completed and that its data should add to the literature on this exciting new technology.
Having participated in the recently completed trial in the United States, I can say that my experience mirrors the metaanalysis. The patients who had positive nodes were identified by both techniques, which was reassuring. In the hands of an experienced surgeon, the learning curve was not steep. The technique was pretty straightforward in thin patients. The signal does attenuate over greater depth, so it was somewhat challenging in obese patients, especially with the plastic instruments and standard retractors (there is a lighted retractor compatible with this system). I did not receive any complaints about occasional skin discoloration; it looks similar in color to what some women experience after radiation. In my practice I did not enroll any patients for whom I planned to use MRI in the future, such as high-risk screening BRCA-type patients; this population is a relatively small minority. The routine use of screening MRI after breast conservation is otherwise of limited value.10
Overall, the authors demonstrate that the use of Sienna+ is noninferior to Tc-99m radiotracer. They also reported that Sienna+ is safe, with no reported significant adverse reactions. This is an exciting new technology that may be an important alternative to Tc-99m radioactive tracer in identifying sentinel nodes for axillary staging, and logistically, it may create more access to patients and surgeons in rural or underserved regions.
The author declares no conflict of interest.
- 9.Teshome et al. Use of a magnetic tracer for sentinel lymph node detection in early stage breast cancer patients: a meta-analysis. Ann Surg Oncol. This issue.Google Scholar