Abstract P3-12-36: The diagnosis and prognosis of ductal carcinoma in situ (DCIS) with microinvasion - Results from the United Kingdom Sloane project
Authors: Shaaban Abeer M , Hilton Bridget , Clements Karen , Dodwell David , Sharma Nisha , Kirwan Cliona , Sawyer Elinor , Maxwell Anthony , Wallis Matthew , Stobart Hilary , Mylvaganam Senthurun , Litherland Janet.Litherland , Brace-Mcdonnell Samantha , Dulson-Cox Joanne , Kearins Olive , Provenzano Elena , Pinder Sarah , Thompson Alastair 
Published: March 2022

Abstract
Background/objectives The natural history of microinvasive carcinoma of the breast (one or more foci of invasion of 1mm or less) and its optimal management remain controversial. We analysed the frequency and outcome of patients with DCIS plus microinvasion within a large prospective cohort of screen-detected DCIS. Methods Patients with screen-detected DCIS diagnosed between 2003 and 2012 with or without microinvasion in the final surgical specimen were identified from the UK Sloane Project database. Comprehensive imaging, surgical, pathology, oncology and subsequent outcome data were collected with a median follow-up of 9 years. Results Among 11285 DCIS patients diagnosed in the UK, microinvasion was reported in 521 (4.6%). The frequency of reported microinvasion varied considerably among screening units (0-25%) but overall decreased from 7% in 2003/04 to 3% in 2011/12.As reported elsewhere, microinvasion was significantly associated with high grade DCIS (5.9% of 7182 cases) compared to 2.9% of intermediate grade and &lt;1% of low grade DCIS (p&lt;0.001, Chi square test). Microinvasion was associated with larger DCIS size (p&lt;0.001) 2.2% of DCIS &lt;10mm, 3.9% of DCIS 10-20mm, 5.8% of DCIS 20-30mm, 5.2% of DCIS 30-40mm and 8.0% of DCIS &gt;40mm had microinvasive foci reported. Microinvasion was also associated with the presence of comedo necrosis (p&lt;0.001), and solid (p&lt;0.001), cribriform (p&lt;0.001) or flat (p=0.03) DCIS architecture.Microinvasion was identified more frequently in patients who underwent mastectomy (6.9%) than in those who had breast conserving surgery (BCS) (3.6%; p&lt;0.001). Axillary nodal surgery was more commonly performed for microinvasion (60.4% compared to 30.3%) including for patients undergoing BCS (43.4% vs 8.5% of all patients with BCS; p&lt;0.001). The rate of nodal metastasis was, however, low and not statistically significantly different between those with and without microinvasion (0.4% and 0.1% respectively, p=0.27).Patients with microinvasion who underwent BCS were also more likely to receive radiotherapy (p&lt;0.001). There was no significant association between the presence or absence of microinvasion with margin status or width. Subsequent events data for England showed that microinvasion was associated with a low rate of ipsilateral subsequent events, with 2.3% of patients having recurrent DCIS and 4.2% developing invasive carcinoma. This was not statistically significantly different from DCIS without microinvasion. All subsequent ipsilateral DCIS events in patients with microinvasion were of high grade. The majority (71.4%) of subsequent ipsilateral invasive carcinomas were of grade 3 compared with only 30.4% of grade 3 carcinomas in patients with DCIS without microinvasion (p=0.02). Breast cancer mortality was significantly higher in women whose tumours showed microinvasion (2.1%) compared with those without it (0.8%; p=0.005). Conclusions Microinvasion was most commonly identified within high-grade DCIS and in larger DCIS lesions, and was associated with comedo necrosis. Its pathological reporting decreased over a 10-year period, but there was significant variation between departments, which requires further evaluation. Patients with DCIS plus microinvasion were more likely to have undergone mastectomy, axillary node surgery and to receive radiotherapy after BCS. Microinvasive breast carcinoma was associated with a low rate of subsequent in situ/invasive events and had a good prognosis but, nevertheless, a higher breast cancer mortality than DCIS without microinvasion.
Citation Format: Abeer M Shaaban, Bridget Hilton, Karen Clements, David Dodwell, Nisha Sharma, Cliona Kirwan, Elinor Sawyer, Anthony Maxwell, Matthew Wallis, Hilary Stobart, Senthurun Mylvaganam, Janet.Litherland Litherland, Samantha Brace-Mcdonnell, Joanne Dulson-Cox, Olive Kearins, Elena Provenzano, Sarah Pinder, Alastair Thompson. The diagnosis and prognosis of ductal carcinoma in situ (DCIS) with microinvasion - Results from the United Kingdom Sloane project [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-36.