Abstract PD6-7: Pathological features and lessons learned from screen detected ductal carcinoma in situ (DCIS) - Results from 11 337 cases in the UK Sloane project

Background: The UK Sloane project aims to improve knowledge of the pathology, radiology and management of DCIS through a UK national prospective audit of in situ carcinoma and atypias. Methods: Phase one included collection of multidisciplinary data on screen detected DCIS, lobular in situ neoplasia (LISN) and atypical ductal hyperplasia (ADH) between 2003-12 through collation of prospective proformas on imaging, pathology, management and subsequent outcome data. Results: A total of 11337 cases of DCIS from 82 UK screening units have been recorded; 54% of cases 40mm and 131 (1%, unknown). There has been a slight but steady increase in DCIS size, from mean of 21.4mm in 2003/04 to 24.1mm in 2011/12. This was largely due to an increase in lesions measuring 30 mm or more. 7213 DCIS cases (63%) were of high nuclear grade, 27% (3121) intermediate and 9% were of low grade (34 unknown grade). A small gradual increase in the proportion of high grade DCIS was noted from 59% in 2004 to 65% in 2012, coupled with a slight decrease in the proportion of low grade DCIS, from 10% to 6% from 2004 to 2012. Comedo necrosis was reported in 61%, more commonly in high grade DCIS (78%) compared with low/intermediate grade lesions (31%). Solid DCIS was the predominant architectural pattern, seen in 61% of cases; 72% of high grade DCIS was of solid pattern, compared with 42% of non-high grade DCIS. Only 3% (233) of patients with breast conserving surgery had margin clearance described as 0mm, with another 3% having disease Atypical ductal hyperplasia (ADH) alone was reported in association with DCIS in 611 patients, of whom 39% had high grade DCIS, 37% intermediate grade DCIS and 24% had low grade disease. In a further 111 patients, ADH and lobular in situ neoplasia were associated with the DCIS, more commonly intermediate (36%) or low grade DCIS (34%) than high grade disease (29%). Lobular neoplasia alone was seen most commonly in patients with high grade DCIS (294 cases, 53%), rather than in patients with low grade DCIS (64, 12%) or intermediate grade disease (190, 34%). ADH and LISN were associated in 6% and 3.6% of cases respectively. Ipsilateral recurrences were almost equally distributed between in situ (n=212) and invasive (n=243) disease (unknown disease in 9 cases). Of the 243 patient who developed ipsilateral invasive disease, 148, 76 and 17 had high, intermediate and low grade disease respectively at presentation (2 original grade unknown). Of the 243 invasive lesions, 148 had a primary diagnosis of high grade DCIS; 66 of these 148 recurrences were also of histological grade 3, 60 were grade 2 and only 10 were of histological grade 1 (12 invasive grade not known). Contralateral lesions were more commonly invasive than DCIS (207 invasive carcinomas and 74 DCIS; 1 unknown). 52 of the invasive carcinomas were of grade 3, 106 grade 2 and 42 grade 1. High grade DCIS was the most common primary disease recorded (174) with 90 intermediate and 18 low grade DCIS. 120 of contralateral invasive cancers had had previous primary high grade DCIS, 72 intermediate and only 15 had had low grade DCIS. Conclusion: The study provides a unique opportunity to understand the histological characteristics and behaviour of screen detected DCIS and the change in the pathological features and management over time. An increase in DCIS size and proportion of high grade lesions is noted. Both ipsilateral and contralateral carcinoma are more common, in the short term, in patients with high grade DCIS but longer follow-up will provide more information. Citation Format: Abeer M Shaaban, Elena Provenzano, Bridget Hilton, Karen Clements, Shan Cheung, Alastair Thompson, Sarah Pinder, on behalf of the Sloane Project Steering Committee. Pathological features and lessons learned from screen detected ductal carcinoma in situ (DCIS) - Results from 11 337 cases in the UK Sloane 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 PD6-7.