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BACKGROUND AND OBJECTIVES: MRI is generally performed to assess response to Neo-adjuvant systemic therapy (NAST) in breast cancer. OBJECTIVE: To assess role of MRI in determining the probability of having residual disease in patients undergoing NAST. We also evaluated synchronous cancers diagnosed following MRI. METHODS: This is a retrospective study which included all patients who had pre-and post-NAST MRI between June 2014 and December 2019. Data on demographics, tumour characteristics and pathology were collected and analysed. Pre- and post-MRI probability were calculated and depicted on nomograms. RESULTS: The study included 205 patients. Overall pre-MRI probability of having residual disease was 55% (OR:1.2). The post-MRI probability was 78% (95% CI 72–83%; OR:3.5) if MRI showed residual disease and 23% (95% CI 16–31%, OR:0.3) if imaging showed complete response. The absolute benefit was higher in TNBC and HR-HER2. Additional cancers were identified in 8.78% of patients. CONCLUSION: MRI is beneficial in evaluating response to NAST specifically in TNBC and HR-HER2 cancers. Pre- and post-MRI probabilities of residual disease depicted on nomograms are a useful tool for clinicians. MRI can potentially impact the treatment decisions by identification of synchronous cancers.

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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 < 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 (>3cm on ultrasound or >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<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.

Introduction: Breast cancer can present as a mammographically occult lesion. Lobular carcinoma has the propensity to develop mutifocal and multicentric disease. Studies have suggested that invasive carcinoma with lobular features have similar biological characteristics as invasive lobular carcinoma. In our unit, patients with mammographicaly occult cancer and those with lobular features on core biopsy have a pre-operative MRI scan. The aim of this study is to assess the impact of contrast enhanced MRI on management of these cases. Methods: Over a 3 year period from November 2012 to October 2015, all breast MRI scans were reviewed and those patients with mammographically occult cancer and invasive carcinoma with lobular features on biopsy were included. Demographic data, imaging, pathology and treatment details were collected from Clinical Information System. A size difference of +/-10% between the imaging modalities was considered to be concordant Results: Out of 389 patients with breast MRI for invasive carcinoma, 104 patients with a median age of 57 years were included. 69 patients (66%) were symptomatic and 35 (34%) were screen-detected cancers. 64 patients had lobular features on core biopsy and 40 patients had mammographically occult cancer. In patients with lobular features group, MRI findings were concordant with mammograms in 26 patients (40%) while 38 ( 60%) had additional findings (28% multifocality, 19% non-concordant size, 6% contralateral findings and 7% ipsilateral benign findings). In patients with non- concordant findings, 58% underwent USS and 24% had biopsy following MRI. In the mammographically occult group, USS identified the primary lesion in 32 patients (80%) while 8 patients (20%) had occult lesion both on USS and mammograms. MRI findings were concordant in 90% while 10% had non-concordant findings (6% multifocality and 4% non-concordant size). Following MRI, 8% had another USS and 3% had biopsy. MRI findings changed the treatment plan in 19% cases with lobular features.14% underwent mastectomy instead of wide local excision, 3% primary chemotherapy and 2% bilateral wide local excision. There was a change in treatment plan in 25% of the mammographicaly occult cancers of which only 6% had lesion visible on USS. 15% of mammographically occult cancers had mastectomy instead of WLE and 10% had neo-adjuvant chemotherapy. Conclusion: This study has demonstrated that pre-operative MRI leads to additional investigations. Its impact on management is low if the lesion is mammographically occult but visible on ultrasound. In cases with ultrasound occult cancer and those with lobular features on core biopsy, it changes management in a significant proportion and should therefore be considered as a part of the diagnostic work-up. Citation Format: Jafferbhoy S, Tandon M, Kirby R, Narayanan S, Bajwa S, Salehi Bird S, Mohd-Isa Z, Soumian S. Selective use of MRI and impact on management in breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-02-10.