Abstract Approximately 30-40% of women are not offered immediate breast reconstruction because the possibility of post-mastectomy radiotherapy (PMRT) is unknown at the time of mastectomy. Breast reconstruction may be delayed until final pathology is available and need for radiotherapy established. Surgical literature is replete with studies of varying quality, reporting complication rates for a range of reconstructive procedures, highlighting the need for surgical trials of reconstructive techniques in women at risk of PMRT. Decisions for these patients are complex, involving multiple clinicians including surgeons and oncologists. To inform a surgical trial design, we aimed to determine current UK surgical practice and gain an understanding of the drivers behind decision-making. Methods: A questionnaire, validated in a pilot population, was posted to Consultant members of the Association of Breast Surgery (UK). We collected data on current practice in conducting Delayed, Immediate and Delayed-immediate reconstructive surgery. We collated data on type and volume of procedure performed and factors affecting decision-making including delay to adjuvant treatment, risk of complications, perception of patients’ quality of life (QoL) and aesthetic satisfaction. Results: Of 355 surgeons, 130(37%) responded. Of these, 77% felt the current evidence base was not adequate to guide surgical decisions and 80% felt a need for further trials to guide best treatment. Despite a lack of scientific evidence demonstrating a difference in cosmesis or QoL between Immediate and Delayed reconstruction, 85% felt there is not equivalent cosmesis and 71% felt there is not equivalent QoL between the two groups. There is considerable heterogeneity in reconstructive approach to patients at risk of PMRT (Table 1). Delayed reconstruction remains the most popular option, being regularly used by 94% of surgeons despite only 34% of surgeons believing the majority of patients are satisfied with the approach. Significantly fewer surgeons perform Immediate implant based reconstruction (with or without ADM) than Delayed (p<0.01). Implant reconstruction is performed by 71% of surgeons in patients at risk of PMRT, but only 44% of surgeons felt patients were happy with the final results. Table 1 No. of responses NeverSometimesOftenAlwaysDelayed5505119Immediate implant584181Immediate ADM+Implant45491452-stage (delayed-immediate) Expander to permanent reconstruction2855335Immediate Autologous2959227 The three most important drivers in making a reconstructive choice were 1. Effect of PMRT on the cosmetic result 2. Minimising risk of complications and avoiding delay to adjuvant treatment 3. Pre-operative uncertainty over the need for PMRT. Conclusions: Surgeons employ a variety of approaches to reconstruction in the face of PMRT, the most common approach being delayed reconstruction. Decision-making is based upon individual surgeon’s perception of risks including likely delay to adjuvant therapy and effect of PMRT on the reconstruction. Drivers appeared to be more surgeon-centred rather than patient-based. There is awareness of a lack of evidence to support decision-making and the need for high quality studies. Randomised clinical trials are needed to provide an evidence base for outcomes. Citation Format: James R Harvey, Nigel J Bundred, Cliona C Kirwan, Ashu Gandhi, Paula J Duxbury. Variation in UK reconstructive practice in the face of post-mastectomy radiotherapy [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P2-14-09.