Abstract P4-09-01: The DCIS score predicts risk of local recurrence risk after breast-conserving surgery more accurately than ER plus HER2

Introduction: Improved individual prediction of 10 yr local recurrence (LR) risk following breast-conserving surgery (BCS) for ductal carcinoma in situ (DCIS) is needed to identify women at low risk, for whom radiotherapy (RT) may be omitted. We hypothesized that LR prediction that includes the Oncotype DCIS score (DS) would be more accurate, and would identify more women with very low LR risks compared to models that include estrogen receptor (ER) plus HER2 without the DS. Methods: Three predictive models of LR (clinicopathological factors (CPFs) alone; CPFs+ER+HER2; CPFs+DS) were developed and compared in 1,102 cases of DCIS for whom complete covariate and outcome data were available. CPFs included age at diagnosis, lesion size, nuclear grade, comedonecrosis, multifocality, and resection margin width. Categorizations of discrete variables and transformations of continuous variables were examined in Cox models; two-way interactions and interactions with time were assessed. Internal validation was performed by bootstrapping. Individual predicted 10-yr LR risks after treatment with BCS alone were computed from covariate values, estimated regression parameters and the estimated baseline survival function. Model performance was assessed by c-statistics and calibration plots. Results: 863/1,102 (78.3%) women were age >= 50 years at diagnosis. Lesion size was = 50 with no adverse CPFs, the CPFs+DS model identified the greatest proportion of women (62.3%) with predicted 10-year LR risk Conclusion: Individual prediction of LR risk that incorporates the DCIS score plus clinicopathological factors is more accurate than prediction models based on ER plus HER2, and identifies a higher proportion of women with a low predicted risk of LR after BCS alone, for whom radiotherapy may be omitted. Citation Format: Rakovitch E, Sutradhar R, Zhou L, Nofech-Mozes S, Hanna W, Paszat L. The DCIS score predicts risk of local recurrence risk after breast-conserving surgery more accurately than ER plus HER2 [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-09-01.