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Purpose The 21-gene recurrence score (Oncotype DX) (RS) informs systemic therapy decision making in ER-positive HER2-negative early breast cancer (BC). To date no study has described the more nuanced discussions that take place regarding systemic therapy or the impact of the RS on concordance in such decision making. Here we utilized a novel decision making tool to assess the impact of the RS on decision making as well as concordance of treatment recommendations. Patients and methods The clinicopathological information (CPI) of 50 BCs without and with the RS were presented to a panel of breast oncologists in a simulated MDT. The Liverpool Adjuvant Systemic Therapy Decision Tool (LASTDT) was developed and used to categorize treatment recommendations. Outcome measures included the impact of the RS on decisiveness and concordance in decision making and its impact on treatment recommendations. Results Availability of the RS increased definitive decision making from 8% (4/50) to 56% (28/50) [χ2 = 79.35, p Conclusions The RS improves certainty of decision making as well as concordance amongst oncologists. This provides evidence that the availability of the RS can improve consistency of decision making amongst oncologists and thus helps to ensure patients are managed consistently. This is particularly important when patients are managed in a loco-regional, multidisciplinary team manner where heterogeneous decisions can lead to disparity in care.

e12108 Background: Neoadjuvant (NA) HER2 blockade with trastuzumab (T) and pertuzumab (P) results in pathological complete response (pCR) rates of 39% to 62%. Diarrhoea is reported in up to 73% of cases. No real-world studies have explored the efficacy and toxicity of this treatment. This study aimed to determine the efficacy and toxicity of NA T-P and CT within a routine NHS clinical practice in the UK. Methods: HER2+ BC patients given NA T-P (accessed via the Cancer Drug Fund) between Oct2016-Jan 2018 at Clatterbridge Cancer Centre NHS Foundation Trust were retrospectively identified. Clinico-pathological information, treatment data, nurse led toxicity and echocardiography were reviewed. Data lock: 30th January 2019. Final pathological response data is presented. Results: 78 female patients were identified with a median age of 50 years (IQR: 44.4-60.2). Diagnosis: median tumour size 30mm (IQR 23.0-47.5mm), 62% (48/78) LN+ & 71% ER+. CT regimens: 81% (63/78) given FEC-DHP; of these 19 (30%) switched to weekly paclitaxel (wP) or nab-paclitaxel; 5% (4/78) AC/EC-DHP; 9% (8/78) TCHP of which 1 (13%) switched to wP. All patients underwent definitive surgery: 50% (39/78) mastectomy & 50% (39/78) WLE. 44% (35/78) axillary node clearance (ANC) & 56% (43/78) sentinel node biopsy (4 prior to NA therapy). 91% (32/35) undergoing ANC were LN+ at diagnosis, of which 66% (21/32) were LN- at surgery. pCR rate (ypT0/is, N0) was 47% (37/78), pCR by HR: ER+ 42% (23/55) & ER- 61% (14/23). pCR for 20 cases switched to wP was 60% (12/20). 6% (5/78) achieved pCR in the breast alone (in these LN status ITCx1, micrometsx3 & macrometsx1). Median size of the 46% (36/78) with residual breast tumour was 14.5mm (1-65mm). Outcome: Median follow up 68 weeks with one local and one distant recurrence occurring but no deaths. Toxicity: Ejection fraction did not decline beyond 10% of baseline in any patients. Diarrhoea occurred in 74% of cases, and CTCAE grade 3-4 toxicity occurring in >2% of patients: diarrhoea, fatigue, and infection. Conclusions: This data confirms 1) the real world efficacy of NA T-P 2) a significant number of LN+ patients become LN- and measures to avoid ANC are needed 3) switching to NA wP is not uncommon and may be associated with a higher pCR 4) diarrhoea rates reflect the literature and measures to mitigate it are needed. Updated outcomes will be presented.