Magnetic Seed Localisation for Non-Palpable Breast Lesions: A Comparison with Hooked-Wire

  

    

    
Magseed® 
    
Hooked-wire 
    
p-value 
  
  

    
Specimen weight (g)1 
    
28.0 [18.0 - 38.0] 
    
30.0 [19.0 - 48.0] 
    
0.337 
  
  

    
Total resected volume (cm3)1 
    
30.4 [19.3 - 43.1] 
    
31.8 [17.7 - 46.9] 
    
0.873 
  
  

    
Percentage resected breast    volume 
    
4.5 [3.1 - 6.0] 
    
3.7 [2.9 - 5.8] 
    
0.049 
  
  

    
Margin status 
    

    

    
0.233 
  
  

    
Negative (%) 
    
80 (95.24) 
    
69 (89.61) 
    

  
  

    
Positive (%) 
    
4 (4.76) 
    
8 (10.39) 
    

  
  

    
1Data    are shown as median [interquartile range].

      2’Not applicable’ includes benign lesions and    lesions with uncertain malignant potential. ’Unknown’ means that the pTN    staging could not be retrieved from the patient’s medical file. 
  

Table 5: Data concerning pathological examination of the specimen.

Surgeon satisfaction

During the first two months, less than 70% of the operations were scored as ’easier than hooked-wire’ by the surgeons, but this scoring exceeded more than 80% by the end of the study.

Discussion

Breast cancer screening and advances in breast imaging have led to more breast lesions being non-palpable at diagnosis. Several alternatives to the gold standard hooked-wire technique have become available. Since September 2018, Magseed^® localisation has become the standard of care for localising non-palpable breast lesions in UZ Leuven. In this prospective observational study, the oncological safety, the clinical safety and surgeon satisfaction of Magseed^® localisation in breast cancer surgery have been prospectively assessed during a period of seven months.

Critical reflection

Placement of the device: All 103 Magseeds^® and 102 hookedwires were placed under ultrasound guidance, with Magseed^® being implanted at a median of two days preoperatively. Regarding hookedwire, a same day procedure is standard whereby dislocation might occur after mammographic control when placed in (large) fatty breast tissue. Occurrence of hematoma during placement was comparable between Magseed^® and hooked-wire.

Detection of Magseed^® with Sentimag^®: Except for one case, a percutaneous signal was present in all patients. Regarding this unique case, several possible explanations have been postulated. First, a possible link with recent pregnancy leading to a larger breast volume and breast density? Patient’s breast volume falls within the third quartile of all breast volumes, but density exceeded the third quartile. However, Harvey et al. showed that Magseed^® is detectable in all breast sizes [5,9]. Secondly, Magseed^® was placed at a depth of 22mm, which is still within the 30mm detection range and even the seed that was placed at a depth of 45mm could be percutaneously detected. Although all precautions were considered and measurements were performed repeatedly, a final explanation might be overlooking interfering factors.

Resected breast volume: In this study, resected volume after Magseed^® or hooked-wire localisation does not show a significant difference. These results correspond with a comparative study performed by Zacharioudakis et al. [7] although with specimen volumes being three times as high as volumes in the current study. Hersi et al. report a median specimen volume of 41.75cm³ with Magseed^® localisation, which resembles more our data [10].

Our data show a significant difference in specimen volume to breast volume ratio with a lower percentage breast volume excised with hooked-wire localisation. Although statistically significant, these results need to be viewed with nuance. As shown in Table 5, specimen volumes between the Magseed^® and hooked-wire group do not show a meaningful difference. In contrast, the estimated breast volume was considerably larger in the latter. Since there was no patient selection, this can be completely assigned to randomity. The combination of a comparable specimen volume but lower breast volume, might explain this difference. Regarding cosmesis after BCS, Cochrane et al. showed that 83.5% of the patients were very satisfied if excised volumes was less than 10% [11]. Another study used an even more stringent threshold of 7.2% at which excellent cosmesis could be achieved [12].

Surgical margins: A positive margin rate of 10.39% was reported in our historical hooked-wire series, which is lower than in literature. Positive margin rate with Magseed^® is considerably lower in our study, even after correcting for ratio of specimen volume to breast volume. Literature reports positive margin rates with Magseed^® localisation from 0% to 16% [6,10,13-15].

Clinical implementation and use of Magseed^®

The implementation of a new methodology in clinical care always implies some trial-and-error in finding a new workflow. Although placing Magseed^® up to 26 days pre-operatively was considered as a logistical advantage, it also involved (logistic) reorganisation between surgeons, radiologists and nurses.

Learning curve: Both radiologists and surgeons experience a short learning curve. For our radiologist, insertion of Magseed^® was similar to the insertion of other tissue markers with comparable challenges regarding characteristics of the tissue. Magseed^® and Sentimag^® were generally described as ’peroperatively easier than hooked-wire’ by surgeons, although some refinements could be formulated. Autocalibration of the probe when not in use, would overcome the need for recurrent calibration. In addition, a wireless probe would also ameliorate clinical use of Sentimag^®.

Applicability: In some cases, Magseed^® did not seem applicable e.g. when tumour tissue was considered too firm for Magseed^® implantation. Later, these hurdles were overcome by placing the Magseed^® near the tumour instead of intralesional. Since Magseed^® signal can be detected over 2cm, nearby-planted seeds can easily guide the surgeon towards the lesion. Furthermore, BCS for a papillary lesion was performed with a hooked-wire because of the loose nature of papillomata. Preference might also be given to hooked-wire in case of multifocality, because inserting more than 1 Magseed^® would rise the cost and could result in an unclear Sentimag^® signal. However, the most important indication wherein a hooked-wire was preferred over Magseed^® was a linear configuration of microcalcifications. The wire could be used as a real guide throughout the zone of microcalcifications to be resected. Lastly, one patient was not suitable for Magseed^® because of an implantable cardioverter defibrillator which is an absolute exclusion criterion for use of Sentimag^®. Other limitations for the clinical integration of Magseed^® include a larger signal void artifact on MRI than caused by other tissue markers and increased cost when compared to hooked-wire. Specifically, the initial start-up cost plus the additional costs for the nonferromagnetic instruments make Magseed^® more expensive than hooked-wire localisation. However, this increased cost is compensated by more efficient and less time-consuming perioperative scheduling.

Limitations and Strengths of this Study

Limitations are mainly related to the monocentric set-up and partly retrospective data collection. The monocentric set-up and limited timeline implie a rather small number of patients, potentially lowering the study power. However, monocentricity can be justified by UZ Leuven being the first hospital in Belgium to adopt Magseed^® as localisation method. Regarding the historical hooked-wire group, the effect of different approaches and practices is probably minimal since the limited number of surgeons, radiologists and pathologist involved in both studies. Secondly, except for the pilot study in October 2017, no formal training program took place, resulting in sporadically suboptimal use of the technique. Data from first experiences with Magseed^® are also included in this study, while the hooked-wire technique was already well-mastered in all included cases. This could slightly distort our data. Lastly, calculating breast volume on craniocaudal view, using VolparaTM often leads to underestimation of the breast volume and might also influence the final result. Nonetheless, the use of an objective software tool also increases the reproducibility of the study and provides more reliable results.

Further strengths are the use of two comparable groups during a comparable time period. No patient selection took place when retrospectively collecting the hooked-wire data. Moreover, surgical experience and techniques are similar because both BCS with Magseed^® and hooked-wire localisation were performed by the same small group of surgeons.

Future Perspectives

Future research might enclose larger and more powered studies to confirm the observed tendency in favour of Magseed^® e.g. tendency to lower positive surgical margins. In addition, objective assessment of patient satisfaction and cosmetic outcome after Magseed^® localisation is desirable, as these topics were currently not investigated. Regarding the latter, obtaining patient derived data is thus crucial in evaluating aesthetics. Furthermore, European approval for long-term placement of Magseed^® was obtained, enabling implantation before neoadjuvant therapy. Placing Magseed^® before start of systemic therapy offers the advantage of avoiding a second invasive procedure since Magseed^® can be placed instead of the standard clip. However, the large signal void artefact on MRI impedes this application in case when BCS is considered, depending on the response to therapy.

Moreover, Magseed^® may have further clinical applications beyond preoperative localisation of non-palpable breast lesions. Magseed^® was also CE approved for the use in any soft tissue, including its use in lymph nodes, lung and thyroid tissue [16]. To explore the feasibility and safety of Magseed^® in targeted axillary dissection and resection of metastases, clinical studies are highly advisable. Furthermore, exploring the extension of Magseed^®’s clinical applicability in other pathologies would also be valuable.

Conclusion

This prospective observational study of Magseed^® localisation compared oncological safety, clinical safety and surgeon satisfaction with a historical serie of hooked-wire localisations for non-palpable breast lesions. In terms of oncological safety, a trend for lower positive surgical margins with Magseed^® was observed, leading to fewer re-excisions and less need for completion mastectomies. A comparable aesthetic outcome, based on resected breast volume, can be expected since specimen volumes were similar between both groups. In respect of clinical safety, all Magseeds^® could be placed under ultrasound guidance with comparable (low) bleeding events. Regarding perioperative scheduling, Magseed^® offers different logistics advantages compared to same-day hooked-wire procedure. In addition, surgeon and radiologist satisfaction with Magseed^® as well as patient comfort are very high. Overall, these results are encouraging to continue using Magseed^® in preoperative breast localisation as well as to explore and broaden its applicability in surgical oncology.

Acknowledgements

The authors acknowledge the Medical Imaging Research Centre, especially Lesley Cockmartin, for providing the Volpara™ software.

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