It’s a very interesting and unusual idea to use magnetism as a way to detect the sentinel node. Can you tell me what you were doing in this study that you’ve now been reporting?
The use of novel alternatives for the identification of sentinel lymph nodes has developed as a consequence of the limitation and logistical aspects of using radioisotopes. Now, novel techniques such as the magnetic technique have been developed for sentinel lymph node biopsy primarily in breast cancer and also in melanoma. What we have done, from our point of view within this study, is to extend that one step further to also perform lesion localisation and concurrent sentinel lymph node biopsy in breast cancer.
Right. Now, you could use radioisotopes, could you use wire for both of those as well?
The current standard treatment for non-palpable breast cancers which provide a high burden of disease, 30% of all breast cancers diagnosed annually are non-palpable and require a localisation procedure. In the majority of the world the standard is for the radiologist to place a wire percutaneously under ultrasound guidance into the lesion so that the surgeon can be guided as to where they excise the lesion intraoperatively. Why should we change this? Well, there are limitations to this. Firstly you have technical and logistical issues with regards to the wire as well as patient satisfaction. Patients don’t like to have a wire extending percutaneously outside the skin and it has to be introduced on the day of surgery because of the risk of migration as well. Consequently, technical limitations result in high re-excision rates and that’s why we want to find an alternative.
So a tracer of some kind is OK and radiotracers have disadvantages?
Exactly. So there have been other techniques which have been developed as alternatives to the wire and that includes radioisotope techniques using the ROLL technique whereby a technetium labelled colloid is introduced to mark the tumour and alternatively also radioactive seeds. But the limitation and wider uptake of these techniques, although they have proven to be beneficial as opposed to the wire, has been their dependence upon radioisotopes. That’s why we’re trying to develop a non-radioisotope and wire-guided free technique for lesion localisation which can also perform sentinel node biopsy.
The suspense is building because I do want to know what your magnetic tracer is.
The magnetic tracer, it’s actually very simple. It’s literally iron oxide which has a sugar coating and it’s dissolved in water, that’s all it is. It has a very small size, 16nm, equivalent to the nanocolloid which is used in sentinel node biopsy.
And then that gets lost in the body when it has done its work?
What happens is the magnetic tracer is injected just using a needle and syringe by the radiologist under ultrasound guidance directly into the tumour, so into the centre. Once it’s in that area we’re able to then use a handheld magnetometer to identify the peak hotspot and direct us towards excision of the tumour. In addition to that a small proportion of the magnetic tracer, certainly less than 2%, can also migrate from the tumour to the first draining lymph nodes i.e. the sentinel lymph nodes of the breast, and they can be used for sentinel lymph node biopsy using the handheld magnetometer.
It sounds really elegant, what have you achieved so far?
So far we’ve got the trial which is running currently, the MagSNOLL trial, Magnetic Sentinel Node and Occult Lesion Localisation, at Guys Hospital, also in Cardiff and we’ve recently also opened within the Netherlands. The numbers that we have reported have included in the first 33 patients in which we’ve performed this procedure. Now initially in the first 13 patients they were patients with palpable breast cancers to confirm the feasibility of the tracer to localise; we subsequently went on to 20 patients who had non-palpable breast cancers. In all these cases we identified 100% successful localisation of the breast cancers and in the non-palpable cohort of 20 there were only two re-excisions which were performed for involved margins. We also obviously performed sentinel lymph node biopsy using this technique and our identification rate was lower than the standard technique, so it was 85% compared to the standard technique of isotope and blue dye of 97% but when combined with blue dye as well as the magnetic technique this also was elevated to 97% as well.
What, then, would you say to doctors about the clinical application of this very interesting new technique?
I think the application is that the magnetic technique for lesion localisation provides a very straightforward radioisotope wire-guided free technique for lesion localisation and also potentially overcomes logistical issues associated with the prior two techniques. Further work, going on forward, could extend the time in which the tracer is actually injected to potentially use it as a biopsy marker in future.
Are you able to say right now that this is going to be the technique of the future?
It’s still early days, this was a feasibility study, but we plan to increase the recruitment and hopefully perform at least a hundred cases before we then consider our next movement which potentially would be to perform a study whereby we randomise against wire-guided localisation. Or, alternatively, also extend the longevity of the tracer within studies and use it as potentially a biopsy marker at the time of diagnosis when patients are recalled from the breast screening programme in order to avoid them requiring a subsequent localisation with its economical benefits.
So the brief take home message to doctors?
The brief take home message is that magnetic nanotechnology has become established for sentinel lymph node biopsy but there are potentially plenty of other applications there. One further future potential application is for lesion localisation.