Magseed (Endomagnetics, Cambridge, U.K.) uses a non-radioactive technology that overcomes the logistical problems and risks associated with using radioactive seed [9]. The first clinical experiences were reported in 2018 in USA and UK. Since than, some studies investigated the accuracy of Magseed. Harvey et al. evaluates the feasibility and positioning of the marker in 29 patients undergoing mastectomy, with excellent results. Prince at al. evaluated Magseed in 64 patients focusing on clinical use, logistical advantages and re-excision rate compared to WGL [13–14].
Both studies concluded that Magseed is an effective and accurate alternative of preoperative breast lesion localization.
Our department surgically treats about 1400 breast cancer patients per year and the most used method for localization of non-palpable breast lesions is skin tattoo. In our experience this method is valid and effective, with a low rate of re-excision [15].
To the author’s knowledge, this is the first study comparing magnetic seed localization with skin tattoo technique.
Patients undergoing neoadjuvant chemotherapy were excluded from the study because at the time of this study Magseed was only licensed to be inserted for up to 30 days prior to surgery. Now the insertion is unlimited, and often performed at the time of biopsy.
We placed 37 seeds in 36 patients. In one case two seeds were located in the same beast, not in close proximity (< 2 cm), so it was easy to separate them. The magnetic seed was successfully located less than 10 mm from the lesion at the control mammogram in 97.6% of cases, maybe because of the good experience of our team in performing interventional procedures.
The time demanded in the localization with seed and skin tattoo was almost the same (12.6 minutes), even in this case, because of the familiarity of our breast radiologists with imaging-guided breast biopsy and localization procedures.
A correlation between localization technique, breast size and lesion depth was observed. The majority of magnetic seeds were placed in medium breasts (B-cup, 62.2%), compared with skin tattoo with a prevalence of small breasts (A-cup, 47.5%), and lesions located at a depth greater for the first one (mean depth was 15.7 mm for magseed and 12.2 mm for skin-tattoo group – p < 0.0001). The seed was not placed deeper than 40mm from the skin surface, according to the detectable of the magnetic seed at greater depths [16].
Magseed was used with greater frequency in patients with small lesions (p = 0.017), smaller than 5 mm in 18.9% of cases.
This data may be used in the clinic to plan localization especially in case of small lesions in large breasts, because of the ease of detection of the seed with the Sentimag probe compared to skin-tattoo.
The longer time between localization and surgery in Magseed group (4.08 ± 15.84, p = 0.146) is due to the placement of the seed days before surgery, differently from the skin tattoo performed the day before or the same day of surgical procedure. It could reduce the weight of the breast radiology services and assist greatly with scheduling.
The migration of the seed from the initial placement was not formally analyzed with an objective parameter, but in our series no seed displacement was observed, and it was in line with the literature [14].
With both methods, 100% of the index lesions were completely removed and found in the surgical specimen. Two cases localized with the Magseed reported presence of DCIS in excision of the surgical margin, as the surgical treatment can be considered as oncologically successful.
A significant difference was observed in the overall surgical time (p = 0.008). The removal of magnetic seed required longer surgical time, despite the presumed advantage of Sentimag as an accurate tool in detecting target lesions. The reason is probably due to the surgeon's poor confidence with this new technique, compared with skin tattoo.
In our experience, Magseed does not differ in terms of oncological efficacy compared to skin tattoo. The site of the lesion in the surgical radiogram, the closest margin and the intraoperative widening were comparable in the two groups [Table 2], according to the previous literature [17].
The less breast parenchyma removed in Magseed group in voluminous breasts (breast/surgical specimen volume ratio 0.98 ± 0.56 vs 2.56 ± 3.05, p = 0.003, Table 3), especially in case of small lesions, revealed that the seed allows to achieve a better aesthetic result, with a clinical value in terms of conservative surgery, not reducing the accuracy.
The re-excision rate reported was 0% for both groups, lower than the generally accepted percentage of 20–25%, (18) maybe due to the small sample size and the administration of loco-regional radiation therapy, according ASCO and ASRO [19].
Micha et al reported that Magseed is better tollereted than the pre-existing standard of guide wires. (20). In our study we have not investigated this aspect.
Moreover, a point to consider is the cost of the Magseed, higher than the standard wire, and obviously than the skin tattoo.
Our study has several limitations. This was a single-center retrospective study, and Magseed was performed at the request of the multidisciplinary team, without a randomization. Despite the homogeneity of the two groups for the histological diagnosis, there is not a perfect match. Moreover, data on cost effectiveness were not evaluated. Due to the nature of the retrospective study, no data were collected on patient satisfaction of magnetic seed vs skin tattoo. Finally, the sample size was small. Our results need to be confirmed by prospective and larger studies.