Abstract PS1-34: Oncological safety and patient journey with magseed™ localised breast conserving surgery
Authors: Kabeer Kirti Katherine , Gowda Manoj S , MohdIsa Zatinahhayu , Thomas Megan , Gopalan Vallipuram , Jafferbhoy Sadaf , Soumian Soni , Narayanan Sankaran , Kirby Robert , Marla Sekhar 
Published: February 2021

Introduction: Wire localised wide local excision (W-WLE) has been the standard of care for impalpable breast lesions and requires insertion of the wire on the same day as the surgery. Logistics of same day localisation can lead to a chaotic morning for the patients with long uncomfortable waiting times prior to their surgery. Transporting patients across the hospital and at times between different sites can add to poor patient experience and inefficient theatre utilisation. Magseed localised wide local excision (M-WLE) is an alternative to W-WLE. Magseed is a 5mm non-radioactive paramagnetic seed inserted radiologically and in the UK it is licensed for insertion up to 30 days in advance. M-WLE was started for routine use in our Unit in July 2019. We compare the safety parameters and length of hospital stay (LOS) in patients undergoing M-WLE to W-WLE. Methods: All M-WLEs performed at a single institution over an 8 month period (Jul 19 - Feb 20) were included. These were compared to a historic matched cohort of W-WLEs performed over 8 months (Jan 18 - Aug 18) which would have been suitable for Magseed localisation. The suitability for Magseed localisation was decided by a breast radiologist based on local objective criteria. Intra-operative cavity shaves were performed based on specimen X-ray and re-excisions were performed where there was tumour at or &lt; 1 mm from inked margin. Exclusion criteria for Magseed localisations included - i. multiple lesions requiring 2 or more wires and ii. Depth of lesion from skin (&gt;3cm on ultrasound or &gt;7cm deep in central breast on mammogram). Data including patient demographics, type of localisation, successful placements, pathology, re-excision rates, tumour size, and length of stay (LOS) was collected and analysed. Results: Over the 16 months, 319 patients underwent localised WLEs. 238 patients were included in the study and 81 excluded. Patient demographics and tumour characteristics are detailed in Table 1. There is no significant difference in the intra-operative cavity shaves between the two groups. A significant difference in the re-excisions rates favouring the M-WLE group despite no significant difference in the mean tumour to specimen ratio was seen. (Table 2) The median waiting time to surgery from the time of admission was observed to be significantly shorter in the M-WLE group (4h15mins vs 7h03mins, p&lt;0.01). There was no significant difference in the median LOS between the two groups (M-WLE 13h44mins, W-WLE 13h56mins, p=0.36). The overall day surgery rates were comparable in the two groups (M-WLE 75.2%, W-WLE 75.1%, p=0.99). Conclusion: In the present series, M-WLE has been shown to be oncologically safe and non-inferior to W-WLE with a significantly lower re-excision rate. In addition to this, the reduced pre-operative waiting time on the day of surgery in the M-WLE group will have a positive effect on the patient journey. Further research should focus on the potential impact on day-bed utilisation and theatre efficiency.

Table 1: Patient demographics and tumour characteristicsMagseed™Wirep valuen105133Median age (years)64 (34-87)60 (28-82)0.05Median BMI28.2 (17-54.4)28.3 (18.8-43.1)0.62PathologyInvasive+/-DCIS851100.31DCIS1715Others38Mean tumour diameter (mm)Invasive+/-DCIS15.19 (3-55)15.52 (1-15)0.82DCIS9.41 (3-45)17.12 (3-55)0.13

Table 2: Tumour to specimen ratio, further intra-operative cavity shaves and re-excision ratesMagseed™Wirep valuen102125Mean Tumour/Specimen RatioInvasive+/-DCIS8.8%18.1%0.20DCIS18.4%24.8%0.75Further intra-operative cavity shavesTotal48 (47.0%)68 (54.4%)0.27Invasive+/-DCIS28/64 (43.7%)56/102 (54.9%)0.16DCIS7/15 (46.6%)8/15 (53.3%)0.71Oncoplastic procedures: Invasive+/-DCIS12/21 (57.1%)4/7 (57.1%)1Oncoplastic procedures: DCIS1/2 (50%)0/1 (0%)NARe-excisions of marginsTotal3 (2.9%)13 (10.4%)0.03Invasive+/-DCIS3/64 (4.6%)8/102 (7.8%)0.4DCIS0/15 (0%)5/15 (33.3%)NAOncoplastic procedures: Invasive+/-DCIS0/21 (0%)0/7 (0%)NAOncoplastic procedures: DCIS0/2 (0%)0/1 (0%)NA

Citation Format: Kirti Katherine Kabeer, Manoj S Gowda, Zatinahhayu MohdIsa, Megan Thomas, Vallipuram Gopalan, Sadaf Jafferbhoy, Soni Soumian, Sankaran Narayanan, Robert Kirby, Sekhar Marla. Oncological safety and patient journey with magseed™ localised breast conserving surgery [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS1-34.