Combined use of magnetic seed and tracer in breast conserving surgery with sentinel lymph node biopsy for non-palpable breast lesions: A pilot study describing pitfalls and solutions

In breast cancer patients with non-palpable lesions, wire or radioactive iodine seed localization are the most common techniques used for accurate preoperative localization to enable an oncologically safe wide local excision [1,2].

Both methods have their disadvantages i.e., wire localizations have a risk of migration and infection, and often causes patient discomfort. Although radioactive iodine seeds do not bear these specific drawbacks, they bring about logistical challenges due to legislation for handling radioactive material which is organized by the department of Nuclear Medicine. Furthermore, there is a necessity for a tracking system of the radioactive seed during the process of insertion until retrieval of the seed out of the tissue, with strict guidelines for transport, handling, and disposal. Alternatively, a non-radioactive seed has been introduced (MagSeed®, Endomagnetics Ltd, Cambridge, U.K.) [3,4]. This MagSeed® is a 5.0–1.0 mm medical grade stainless steel seed with magnetic detection property. Under imaging guidance, the MagSeed® is placed in the center of the tumor by ultrasound or stereotactic mammography and can be localized with a magnetic detector probe (Sentimag®, Sysmex, GmBH, Hamburg, Germany) during surgery. Several studies have shown that the MagSeed® is non-inferior to wire-localization for non-palpable breast lesions with a retrieval rate of 100% [[3], [4], [5], [6], [7], [8], [9], [10]].

The advantages of non-radioactive seeds are only utilized to the fullest when they are incorporated in a totally radioactive-free surgical procedure. When performing surgery for clinically node-negative breast cancer, the procedure is usually paired with a sentinel lymph node biopsy (SLNB) using a radioactive tracer. Lymphoscintigraphy using Technetium-99m (99mTc) nano colloid is widely used for detecting the sentinel lymph node (SLN)and is generally considered as the gold standard [11,12]. This procedure requires a logistic planning in combination with the nuclear medicine department as the radioisotope tracer must be injected in a small window of time in relation to the surgical procedure. Moreover, the same legislation, strict guidelines, and hazards associated with handling radioactive materials apply. The use of a non-radioactive tracer could be a good alternative in avoiding these issues.

Equivalent to the non-radioactive seed, a non-radioactive tracer for identification of SLN has become available [13,14]. This tracer (MagTrace®) consists of superparamagnetic iron oxide carboxydextran-coated nanoparticles with a size of 59 nm, it is transported through the lymphatic vessels and filtered by the SLN's, and can be detected using the same magnetic detector probe (Sentimag®, Sysmex, GmBH, Hamburg, Germany) as used for the detection of the MagSeed® during surgery [15,16]. The use of the magnetic SLN technique with magnetic tracer is safe and equivalent to the gold standard with Tc99-nanocolloid [[17], [18], [19]].

Combining the use of the paramagnetic seed and tracer allows breast conserving surgery with SLNB without the use of radioactive materials. This would match the principle of ALARA (As Low As Reasonably Achievable [20]) to refrain from the use of radioactive sources whenever possible, leading to improved logistics as it omits the requirement of a nuclear medicine department. Furthermore, it improves logistics regarding surgical planning in specific time frames related to the timing of tracer injection. Studies on the combined use of the magnetic seed and tracer are limited and focus mainly on detection rates, rather than providing a detailed approach on how to avoid practical problems [16,18,19,[21], [22], [23]].

In this pilot study we describe our first experience with the use of the combination of MagSeed® and MagTrace® for breast conserving surgery and SLNB in patients with non-palpable breast lesions. We define pitfalls we encountered during implementation of this combined technique and provide solutions resulting in an instruction manual for totally radio-active free procedure.

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