Abstract P4-15-02: Impact of radiotherapy and endocrine therapy on further events: Final multivariate analysis of a prospective, national cohort study of screen detected ductal carcinoma in situ (DCIS) of the breast

Key words: DCIS, radiotherapy, endocrine therapy, survival, surgical margins Background: The benefits and risks of breast screening remain controversial, with particular concern that ductal carcinoma in situ (DCIS) may be over-diagnosed and over-treated. There is little prospective data on treatment or outcomes for screen detected DCIS. Methods: A prospective cohort of non-invasive lesions diagnosed through the United Kingdom National Health Service Breast Screening Programme (NHSBSP) (1 April 2003 to 31 March 2012) was linked to national databases and case note review to analyse patterns of care, recurrence and mortality. Results: Screen-detected DCIS in 9938 women was analysed, 33% (9938/30041) of women with a final diagnosis of non-invasive breast neoplasia diagnosed through the NHSBSP over the same time. The patients (mean age was 60 years: range 46-87 years) were treated by breast conservation surgery (BCS; 7007; 70.5%) or mastectomy (2931). At 64 months median follow up, 697 (6.8%) had further DCIS or invasive breast cancer after BCS (7.8%) or mastectomy (4.5%) (p Breast radiotherapy (RT) after BCS (4363/7007; 62%) was associated with a 3.1% absolute reduction in any ipsilateral DCIS or invasive cancer (No RT: 7.2% vs RT: 4.1% (p Among 321 (3.2%) women who died, 46 deaths (0.5%; 14.3% of all deaths) were attributed to invasive breast cancer. Death from breast cancer was uncommon and outnumbered 5:1 by death due to other causes. RT after BCS was associated with a non-significant 0.2% absolute reduction in breast cancer mortality. However, women who developed invasive breast cancer had a worse survival than those with further DCIS (p Conclusions: Recurrent DCIS or invasive cancer is uncommon following screen detected DCIS treated by surgery and adjuvant therapy. Both RT and endocrine therapy following surgery were associated with a significant reduction in further DCIS and invasive disease, but not breast cancer mortality, within 5 years of diagnosis. This study quantifies the benefits of radiotherapy and endocrine therapy to inform decision making in the management of screen detected DCIS. Citation Format: Thompson AM, Clements K, Cheung S, Pinder SE, Lawrence G, Sawyer E, Kearins O, Ball GR, Tomlinson I, Hanby AM, Thomas J, Maxwell AJ, Wallis MG, Dodwell DJ. Impact of radiotherapy and endocrine therapy on further events: Final multivariate analysis of a prospective, national cohort study of screen detected ductal carcinoma in situ (DCIS) of the breast [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-15-02.