Paramagnetic Seeds: An Effective Option for Breast Lesion Localization

Paramagnetic seeds along with superparamagnetic iron oxide (SPIO) was an effective combination for nonpalpable breast lesion localization and sentinel lymph node detection (SLND), data from the MAGTOTAL trial in Sweden showed.

The totally magnetic technique was equivalent to the use of guidewire and SPIO regarding re-excision frequency at 2.84% versus 2.87%, for a difference of -0.03% (95% CI -3.20% to 3.20%, P=0.99), reported Andreas Karakatsanis, PhD, of Uppsala University Hospital in Uppsala, and colleagues.

Resection ratios in this trial were also similar between the trial arms, regardless of previous physician experience or practice patterns (median 1.93 vs 2.01, P=0.70), “suggesting that adaptation is safe,” they wrote in JAMA Surgery.

“Moreover, in the center with the highest experience, the resection ratio in the totally magnetic arm was 0.3 lower (1.26 vs 1.57) and one of the lowest reported in the literature with only 0.9% re-excisions,” the authors added. “Although this did not reach statistical significance, it is indicative of how familiarization with the technique yields potential for precision surgery and resection of smaller specimens.”

Karakatsanis and colleagues noted that breast cancer screening, as well as improvements in imaging, have led to an increase in the diagnosis of nonpalpable breast cancers.

Breast-conserving surgery is feasible, but preoperative tumor localization is required. The guidewire is used extensively for breast tumor localization, but it is associated with complications such as dislocation, migration, and patient discomfort, they said, also noting that “[a]part from these complications, guidewire localization is restricted to the day of surgery, posing logistical challenges.”

While paramagnetic seeds have demonstrated promising results, this is the first randomized trial comparing paramagnetic seeds and guidewires, according to an accompanying invited commentary.

Lena Turkheimer, MD, MPH, and Shayna Showalter, MD, both of the University of Virginia in Charlottesville, said the trial demonstrated that the use of paramagnetic seeds and SPIO for localization “was shown to be both patient- and practitioner-centric without compromising surgical outcomes.”

They also noted that while cost efficiency analyses of the procedures are pending, the benefits of using the magnetic seed technique regarding patient and practitioner satisfaction, improvements in efficiency, and a decrease in reoperation rates, “may mitigate the start-up costs and result in opportunity cost savings overall.”

The phase III trial took place at three hospitals in Sweden from May 2018 through May 2022 with 426 women (median age 65) who had nonpalpable ductal cancer in situ (DCIS) or T1-T3 invasive breast cancer. They were scheduling for breast-conserving surgery and SLND.

The authors observed that overall SLND was 98.6%, with no differences between guidewire and seed arms (98.1% vs 99.0%, difference -0.9%, 95% CI -3.6% to 1.8%, P=0.72), and that more failed localizations occurred with the guidewire (10.1% vs 1.9%, difference 8.2%, 95% CI 3.3%-13.2%, P<0.001).

“In addition, seed and SPIO resulted in shorter operative times and increased satisfaction among health care practitioners,” they stated.

Median time to specimen excision was shorter for the seed (15 vs 18 minutes, P=0.01), as was the total operative time (69 vs 75.5 minutes, P=0.03). Also, providers involved with the surgery — 15 surgeons, four radiologists, and six surgical coordinators — graded their experience with the two procedures based on a Likert scale of 0 to 10, with results showing that satisfaction was higher with the paramagnetic marker across all disciplines.

Trial limitations included the fact that the interventions were unmasked which may have led to some performance bias. Also, the authors said they could not account for “[d]ifferences in surgical style…which may be the reason for differences among sites, but, reassuringly, not between trial arms.”

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