Sentinel Node Biopsy Using Magnetic Tracer Versus Standard Technique: The SentiMAG Multicentre Trial: A Reply

See original letter here.

Letter to the Editor

Michael Douek,1 Bauke Anninga,1 Joost Klaase,2 Ian Monypenny,3 and Bennie ten Haken,4 on behalf of the SentiMAG Trialists Group

1King’s College London, London, UK; 2Medisch Spectrum Twente, Enschede, The Netherlands; 3University Hospital of Wales at Llandough, Cardiff, UK; 4University of Twente, Enschede, The Netherlands

To the Editors:

We thank Prof Barranger and Dr Ihrai for their interest in our recently published article in Annals of Surgical Oncology [1]. We agree that sentinel lymph node biopsy (SLNB) using the combined technique is standard practice in breast surgery for patients who are clinically (and radiologically) node negative [2, 3]. Prof Barranger and Dr Ihrai acknowledge the drawbacks of radioisotope use and recognize the importance of evaluating this new magnetic technique to perform SLNB.

The SentiMAG Multicentre Trial was the first to demonstrate the feasibility of the magnetic technique for SLNB. There are important differences between the magnetic and the standard techniques. For instance, surgeons need to be aware of the diamagnetic effect (magnetic signal from water in skin and underlying tissue) and need to correct for this by balancing the device, prior to performing skin measurements or measurements within the surgical wound. We agree that the magnetic technique does have a learning curve and as with any novel surgical procedure, requires training. All surgeons that participated in the trial were trained by the chief investigator (MD) and also by the principal investigators to standardize surgical procedure (with respect to the magnetic technique) in accordance with the trial protocol and Standard Operating Procedure (SOP).

The authors’ identify the diameter of the hand held probe as the main technical disadvantage causing an enlargement of the incision. The size of the probe was noted as a disadvantage within the trial but not as an important issue. This was not reported as leading to an increase in the size of the incision, although the incisions were not measured within this trial. As part of the standard technique surgeons palpate the wound for any enlarged nodes and this clearly requires an incision large enough to do so. The magnetic signal is stronger when the probe is in contact with the node but a signal is detectable within approximately 2.5cm – 3cm of a node (with or without tissue in between).  A probe with a smaller diameter is under development by the manufacturers.

A more important drawback was the need to remove metal retractors from the wound when using the hand held probe and this was mentioned in our article [1].  Good quality non-metallic instruments are available and were used by some surgeons within the trial.  Another issue raised was the need to balance the device regularly (and this takes a total of 5 seconds each time), which we do not feel could add significant time to the operation.

We agree with the authors that this technique requires further technical improvements, which are currently being evaluated. We feel that an independently run (non-commercial) randomized controlled trial is required before clinical practice can be changed and that the combined technique remains the standard of care.


1. Douek M, Klaase J, Monypenny I, Kothari A, Zechmeister K, Brown D, Wyld L, Drew P, Garmo H, Agbaje O et al: Sentinel Node Biopsy Using a Magnetic Tracer Versus Standard Technique: The SentiMAG Multicentre Trial. Ann Surg Oncol. 2014; 21:1237-1245

2. Cody HS, 3rd, Fey J, Akhurst T, Fazzari M, Mazumdar M, Yeung H, Yeh SD, Borgen PI: Complementarity of blue dye and isotope in sentinel node localization for breast cancer: univariate and multivariate analysis of 966 procedures. Ann Surg Oncol 2001; 8:13-19.

3. Lyman GH, Giuliano AE, Somerfield MR, Benson AB, 3rd, Bodurka DC, Burstein HJ, Cochran AJ, Cody HS, 3rd, Edge SB, Galper S et al: American Society of Clinical Oncology guideline recommendations for sentinel lymph node biopsy in early-stage breast cancer. J Clin Oncol 2005, 23:7703-7720.

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