Abstract P6-16-03: Surgical management of DCIS during the UK Sloane audit project

Introduction The Sloane Project is a prospective cohort study, including 50% of United Kingdom screen detected ductal carcinoma in situ (DCIS) (2003-2012). We sought to examine the trends in surgical management over time for screen detected DCIS. Methods Trends in type of breast surgery were compared with DCIS radiology, pathology and breast size. Results Of 9945 patients with complete data undergoing surgical excision, 2274 (22.9%) underwent mastectomy as their first procedure, of whom 1581 (69.5%) had a simple mastectomy. Among 7877 undergoing attempted breast conserving surgery (BCS), 83 (1%) had therapeutic mammoplasty (TM). The 4:1 attempted BCS:mastectomy ratio remained consistent over time. Of attempted BCS, 882 (11.2%) were ultimately converted to mastectomy (28.9% reconstructed). Over the decade, preoperative radiological estimation of DCIS remained constant at 26mm, however pathological DCIS size steadily increased from 22.4mm (2003-4) to 25.3 (2011-12). There was no corresponding increase in mastectomy, completion mastectomy or re-excision rates. Mean tumour size excised at BCS was 19.3mm (mean), at TM was 32.4mm and at mastectomy was 39.8mm. The rates of simple mastectomy (vs reconstruction) decreased from 77.7% to 61.2% while there was a small increase in TMs (from 0.2% (2 patients) [2003-4] to 1.7% (15 patients) [2011-12]). There was a statistically (but small [8%] clinically) significant difference in mean breast volume for BCS compared to mastectomy patients (1068ml vs 988ml respectively, Student’s t-test p Conclusion Breast size and pathological size, but not radiological size of screen detected DCIS increased between 2003 and 2012, but BCS rates remained consistent. Interestingly, breast size had no apparent influence on type of surgery, although the decrease in simple mastectomy suggests breast reconstruction increased over time. Citation Format: Cliona Clare Kirwan, Sheila Stallard, Senthurun Mylvaganam, Bridget Hilton, Karen Clements, Shan Cheung, Alistair Thompson. Surgical management of DCIS during the UK Sloane audit project [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-16-03.